Category: Chemistry Notes PPT

There are multiple rules which we need to understand before we actually go on explaining Hund’s rule. First, we will look into Aufbau’s rule, understand it and then go to Hund’s rule.

In Aufbau’s principle section, we discuss how the electrons fill the lowest energy orbital first and then move up to higher energy orbital is only after they have filled the lower energy orbitals when we look at it from a very deep perspective we can figure out that the 1s orbitals should technically get filled before the 2s orbital because of the lower value that 1s orbital has which in turn gives it lower energy so from this theory, where we see a problem with think of a solution and provide an answer to this question which involves Hund’s rule.

Now Hund’s rule states that every orbit in a sub-level is occupied singly before any orbit is doubly occupied.

To maximise the total spin of the electron, all of the electrons in singly occupied orbitals have the same spin.

When the electrons are assigned to the orbital is, similar energy is required by N electron to fill or the orbital is, which is also referred to as degenerate orbitals, this is before pairing with another electron in a half an orbital. Add the ground states atoms tend to have a huge number of unpaired electrons. 

To understand this we can visualise the process of electrons which exhibit the same behaviour as the same poles of a magnet would if they come into contact, as negatively charged electrons filled orbitals, the first try to get as far as possible from each other before having to better.

Electrons are negatively charged because of which they ripple each other, so we see that electrons tend to minimise repulsion by first occupying their own orbitals rather than sharing an orbital with another electron now according to quantum mechanical calculations it is shown that the electrons in singly occupied orbitals are less effectively screened or shielded from the nucleus, which can be called as electron shielding.

Now explaining the second rule, if it speaks technically, the first electron in a sublevel could be either spin up or spin down. The spins of all the electrons in a given sub-level depend on the span of the first electron which is chosen in a sublevel. So we can simply say that when the spin of the first electron in a sub-level is chosen, the spins of all the other electrons in that particular sub-level depend upon the first spin.

To figure these equations out we need electron configurations, it is very difficult to understand when put in a theoretical manner so it is very important to understand the configuration, orbitals, properties, place on the table, etc.

In any whichever case it is the outermost electron of the atoms that come into contact with one another or valence shell that interacts first and an atom which is least stable (and most reactive) can be seen when its valence shell is not full, it is very important to note that the valence electrons are hugely responsible for elements chemical behaviour because elements that have the same number of valence electrons of all tend to have similar chemical properties. 

Configurations also help us in predicting the stability of an atom, the most stable configuration is that we see are the ones that have full energy levels, which occurs in the noble gases. This particular stability of these elements makes noble gases very neutral and that is why they do not react easily with any other elements. 

When we read about chemical compounds or any gas, it is very important to make predictions about how certain elements will react or what kind of chemical compounds or molecules different elements will form, and with the help of electron configurations, we can do these tasks easily.

Electronic Configuration – Pauli’s Exclusion Principle, Aufbau Principle and Hund’s Rule

Electrons

Electrons are small compared to protons and neutrons, over 1,800 times less than either a proton or a neutron. Electrons have a relative mass of 0.0005439 such that the electron is compared with the mass of a neutron being one or about 9.109×10^-31kg.

The electron was discovered in the year 1897 by British physicist J.J. Thomason. Basically known as “corpuscles,” electrons have a negative (-ve) charge and are electrically pulled to the positively charged protons. The atomic nucleus is surrounded by electrons in pathways called orbitals; this idea was put forth by Erwin Schrödinger, a physicist, in the 1920s. Now, this model is known as the quantum model or the electron cloud system. The inner orbitals surrounding the atom are Spherical, but the outer orbitals are much more complex.

An atom’s electron configuration is the orbital description of the positions of the electrons in a typical atom. Using the electron configuration and laws of physics, chemists can predict an atom’s properties, such as stability, boiling point, and conductivity.

Electronic Configuration

It is the method or distribution of electrons in the orbitals of an atom. An atom comprises subatomic particles like electrons, protons, and neutrons among which only the number of electrons is considered for electronic configuration. Electrons are supplied in such a way that they achieve a high constant configuration.

The atom consists of s, p, d, and f orbitals in which s orbital can hold a maximum of 2 electrons in them,

The p orbital can hold a maximum number of 6 electrons, ‘d’ orbital can hold a maximum number of 10 electrons and the f orbitals can hold a maximum number of 14 electrons in the orbital shell.

For Example: Chlorine 17

1s²2s²2p⁶3s²3p⁵. 

In the above distribution of electrons, orbitals in which s orbital can hold a maximum of 2 electrons in them, the p orbital can hold a maximum number of 6 electrons

Shell 

The electron shells are named by K, L, M, N, O, P, and Q; or by 1, 2, 3, 4, 5, 6, and 7; going from innermost shell to outermost shell. Every shell is formed by one or more subshells, which are formed by the composed of atomic orbitals it is called as the subshell 

 

Electron Spin

Electron spin is a quantum feature of electrons. It is a kind of angular momentum. The magnitude value of this angular momentum is permanent. Like charge and rest mass, spin is a basic, unvarying property of the electron.

As a teaching method, we can sometimes liken electron spin to the earth spinning on its own axis every 24 hours. If the electron spins clockwise on its axis, it is called spin-up and if it is counterclockwise then it is called spin-down. This is a suitable explanation, if not fully justifiable mathematically.

The spin angular momentum linked with electron spin is independent of orbital angular momentum, which is associated with the electrons that travel around the nucleus.

Laws

They are three important laws that fulfill these electrons namely

1. Pauli’s exclusion principle

2. Aufbau principle

3. Hund’s rule.

Pauli’s Exclusion Principle

According to this law, an orbital cannot have both the electrons in the same spin motion (half-integer spin); electrons will be in either positive half spin (+1/2) or negative half spin (-1/2)

For example, argon’s electron configuration:

1s² 2s² 2p⁶ 3s² 3p⁶

The 1s level can accommodate two electrons with the same n, l, and ml quantum numbers. Argon’s pair of electrons in the 1s orbital meet the exclusion principle because they have opposite spins, determining they have different spin quantum numbers, ms. One spin is +½, the other is -½. (Instead of saying +½ or -½ often the electrons are said to be spin-up up arrow or spin-down down arrow.)

The 2s level electrons have a separate principal quantum number to these in the 1s orbital. A couple of 2s electrons differ from each other because they have different spins.

The 2p level electrons have a different orbital angular impulse number from those in the s orbitals, hence the letter p rather than s. There are three p orbitals of similar energy, px, py, and pz. These orbitals are different from one another because they have different bearings in place. Each of the px, py, and pz orbitals can contain a pair of electrons with opposite spins.

The 3s level rises to a greater principal quantum number; this orbital accommodates an electron pair with opposite spins.

The 3p level’s information is similar to that for 2p, but the principal quantum number is higher: 3p lies at higher energy than 2p.

Aufbau Principle

This principle explains filling up electrons in rising orbital energy.

For example, 1s orbital should be fulfilled before 2s orbital for 1s is lower in energy than 2s orbital. 

By regarding these three rules, the electron configuration of an atom is composed.

For example, the electron configuration of the Carbon atom. 

Carbon is a p block element that includes 6 electrons. It comprises s and p orbitals. Hence by grasping the three rules the electronic configuration of the carbon atom can be written as, 1s²2s²2p²

The electron configuration for the carbon atom is recorded as. The total no of 6 electrons is disposed over 1s, 2s, and 2p orbitals. s orbitals can hold two electrons and p orbital holds 2 electrons by following Hund’s rule of highest multiplicity.

Hund’s Rule

According to this principle, for a given electronic configuration, the paring of the particle is done after each subshell is filled with a single electron. In other words, the under subshell should have maximum multiplicity.

 Hund’s rule states that:

When allowing electrons to orbitals, an electron first seeks to fill all the orbitals with comparable energy (also called degenerate orbitals) before joining with another electron in a half-filled orbital. Atoms at ground states tend to have as many unpaired electrons as likely. 

In reflecting this process, consider how electrons show the same behavior as the same poles on an attraction would if they came into contact with each other; as the negatively charged electrons fill orbitals, they first try to get as far as possible from each other before having to match up.

According to the first principle, electrons always start with an empty orbital before they join up. Electrons are negatively charged and, as a result, they resist each other. Electrons tend to reduce objection by occupying their own orbitals, rather than receiving or accepting an orbital with another electron. 

Furthermore, quantum-mechanical computations have shown that the electrons in only filled orbitals are small, adequately screened, or shielded from the nucleus. Electron shielding is further discussed at the next level.

For the second principle, unpaired electrons in only filled orbitals have similar spins. Technically speaking, the first electron in a subshell could be either “spin-up” or “spin-down.” 

Once the spin of the first electron in a subshell is chosen, however, the spins of all of the separate electrons in that sub-shell depend on that first spin. To avoid interference, scientists typically draw the first electron, and any other unpaired electron, in an orbital as “spin-up.”

For Example:

Carbon and Oxygen 

Considering the electron configuration for carbon atoms: 1s²2s²2p², the two 2s electrons will fill the similar orbital, whereas the two 2p electrons will be in various orbital (and aligned in the same direction) in accordance with Hund’s rule.

Consider the electron configuration of oxygen. Oxygen has 8 electrons. The electron configuration can be written as 1s²2s²2p⁴. To draw the orbital diagram, begin with the subsequent observations: the first two electrons will pair up in the 1s orbital shell; the next two electrons will pair up in the 2s orbital shell. That leaves 4 electrons, which must be placed in the 2p orbital shell. 

According to Hund’s rule, all orbitals will be once filled before an electron is double filled. Therefore, two p orbital get one electron and one will have 2 electrons. Hund’s rule also specifies that all of the unpaired electrons must have the same spin. In keeping with practice, the unpaired electrons are drawn as “spin-up”.

Answer the following question:

1. What is an electron?

2. Define the term electron spin?

3. State Hund’s rule?

4. Explain Pauli’s exclusion principle?

Fill in the blanks:

1. The electron was discovered by __________, a British physicist in the year 1897. (Ans: J.J. Thomason)

 2. Every shell is formed by one or more subshells, which are formed by the composed of atomic orbitals it is called as ________ (Ans: subshell)

3. Unpaired electrons in only filled orbitals have similar spins. Technically speaking, the first electron in a subshell could be either ______________. (Ans: “spin-up” or “spin-down.”)

4. The p orbital can hold a maximum number of ___ electrons, ‘d’ orbital can hold a maximum number of __ electrons and f orbitals can hold a maximum number of _____ electrons in the orbital shell. (Ans: 6, 10, 14)

Conclusion

This is all about Hund’s Rule and the principles related to it. Understand the explanation well and find out how electrons are configured in the shells outside the nucleus of an atom. 

Hydrogen is one of the simplest elements consisting of one electron and one proton. Moreover, it is most abundantly present in nature. However, it is not present in its gaseous form on the earth naturally. This simple element is always found combining with other elements and forms compounds like water H2O.

However, for the past few years, scientists have researched and found that hydrogen can be used as an alternative fuel – hydrogen fuel. Furthermore, its popularity is inclining drastically as this fuel is capable of producing a huge quantity of heat on combustion.

So, what is a hydrogen fuel cell? And what are hydrogen fuel cells used for? You can find all answer related to this fuel option in the following content.

What is Hydrogen Fuel?

First, you must understand what is hydrogen fuel. It is a zero-emission fuel which is produced burning of hydrogen with oxygen. Also, you might get astonished by the fact that this alternative fuel can release a greater amount of energy compared to petrol and diesel. More specifically, it is three times more efficient than petrol.

Furthermore, while burning, hydrogen fuel produces a lot of lesser pollutants than petrol or diesel. Nearly around 95% of hydrogen is formed by steam reforming of fossil fuels or by partial methane oxidation.

However, by coal gasification or water electrolysis, hydrogen can also be produced with zero carbon emission. Other than these processes, certain bacteria and algae also release hydrogen by utilising sunlight under specific conditions. Organic compounds, precisely the hydrocarbons that create several fuels like natural gas, gasoline, propane, and methanol, are also a large source of hydrogen fuel.

Hydrogen Fuel Cell

To know about hydrogen fuel cell, at first you should know what a fuel cell is.

A fuel cell is a mechanical device that can convert the energy captured within molecular bonds or chemical potential energy into electrical energy. Now, the proton exchange membrane of a hydrogen fuel cell uses hydrogen and oxygen as fuels. This PEM cell combines oxygen and hydrogen to create heat, electricity, and water.

The anode of this fuel cell carries hydrogen, and the cathode carries oxygen. Here, these hydrogen molecules divide into protons and electrons at the anode part of the cell. And due to the applications of hydrogen fuel cells, these two elements react, and these cells produce a huge amount of energy.

Thus, often, this fuel cell is compared to batteries. Both fuel cells and batteries produce energy via chemical reactions and transfer that energy into workable electric power.

Key Points

• Hydrogen fuel carries nitrogen oxides or NO as pollutants. This is because hydrogen molecules treat nitrogen gas as one of the impurities. 

• By adding water to the cell container, this pollution can be further reduced. This process can prevent the reaction of nitrogen and oxygen.

• As you know, hydrogen belongs to the first place in the periodic table as it is lighter than air. So, a fuel cylinder containing hydrogen can weigh much lesser than of petrol or diesel. 

• The temperature needs to be decreased at 20 K to keep hydrogen gas into a liquid state. However, due to the produced heat in reaction, this becomes quite difficult. Thus, it is affecting fuel efficiency. Now, scientists around the globe are researching to find out a way to use hydrogen fuel more simply.

So far, you have learnt some basic yet important information to answer what is a hydrogen fuel cell, and how does it work. 

Quiz 1.0

1. What is the process used in a hydrogen fuel cell to generate electricity?

Options:

1. Fusion

2. Organic reaction

3. Combustion

4. Electrochemical reaction

2. What does fuel cell emit?

Options:

1. Carbon

2. Water

3. Oxygen

4. Hydrogen

3. How can you increase the electricity amount of a fuel cell mechanism creates?

Options:

1. Supplying more oxygen

2. Supplying more hydrogen

3. Supplying more protons

4. Supplying more cells

4. What is the process of refuelling a fuel cell vehicle?

Options:

1. Refuel with water

2. Plug it into an electric charging station

3. Pump hydrogen into the fuel tank

4. Fill the tank with gasoline.

5. What percentage of the known universe is composed of hydrogen?

Options:

1. 75%

2. 50%

3. 99%

4. 25%

Answers

1. d. Electrochemical reactions. Fuel cells produce electricity via electrochemical reactions similar to a battery without combustions. However, contrary to a battery, a fuel cell does not wear out as long as there is a continuous fuel source.

2. b. Fuel cells only emit water, heat, and energy.

3. d. Multiple fuel cells are merged to come up with fuel cell stack to boost the amount of electricity produced. As one fuel cell can produce nearly one volt of electricity, the stack can create more.

4. c. To refuel a fuel cell vehicle, you need to fill the tank with hydrogen directly from a fuel station.

5. a. 75%.

Hydrogen Fuel Production

As said earlier, even though hydrogen is abundantly available in the atmosphere, it is not found in its pure form. Hydrogen composes almost 75% of all substances present in the universe. However, for an industrial scale of usage, it needs to be present as primary energy. 

Here are some conventional methods for the production of hydrogen fuel.

Besides these methods, some other hydrogen production processes are in developmental or research phase. Some of these methods are the photobiological, high-temperature, and also photoelectrochemical splitting of water.

Uses of Hydrogen Fuel

The main uses of hydrogen fuel cells are an alternative power option for aeroplanes, cars, boats, etc. It can be used as a portable or stationary application of fuel cell that can power electric motors. However, it is not easy to store H2 in high pressure or cryogenic tank. And that is a primary problem of considering hydrogen fuel cell in vehicles.

Quiz 2.0

1. Which are the most popular methods to produce hydrogen fuel?

Options:

1. Quantum mechanics

2. Thermal conductivity

3. Electrolysis and steam reforming

4. Electrolysis and absorption

2. In which year the first-ever fuel cell was invented?

Options:

1. 1920

2. 1789

3. 1894

4. 1839

3. What are the by-products of the fuel cell system?

Options:

1. Water vapour and heat.

2. Water and carbon dioxide.

3. Water and carbon monoxide.

4. Water and hydrogen monoxide.

4. Which one is the major setback of the fuel cell mechanism?

Options:

1. Pollution

2. Weight

3. Cost

4. Longevity

5. Where in a fuel cell are hydrogen ions produced?

Options:

1. Anode

2. Cathode

3. The positive terminal of a battery

4. Electrolyte centre 

Answers

1. c. Electrolysis and steam reforming are the two most cost-effective and common processes to produce hydrogen.

2. d. In the year 1839, Sir William Robert Grove invented first-ever fuel cell. 

3. a. Water vapour and heat are the by-products of this fuel cell system.

4. c. Cost is one of the significant downsides of this mechanism.

5. a. Hydrogen ions are generated in the anode cell.

Hydrogen Economy

• Hydrogen economy implies a vision of considering hydrogen as an alternative power generator with low-carbon emission. For example, one of the objects of this fuel cell is to replace natural gasses as heating fuels or gasoline as a fuel for transportation.

• The elemental benefit of this system is that here hydrogen instead of electricity transmits the energy.

• In present day, it is operated by combining with natural gasses to enhance efficiency. Moreover, in the near future, this fuel is expected to be used widely.

Hydrogen Fuel: Advantages

• The main advantage of a hydrogen fuel cell is that it only emits water. Thus, it is eco-friendly.

• While burning, hydrogen does not generate carbon dioxide.

• Electrolysis and steam reforming

• The fuel cell engines are more efficient than an internal combustion engine.

Now, you must have understood the importance of hydrogen fuel cell in human life as well as the environment. If you need any more information about what is a hydrogen fuel cell and its uses, advantages, etc., you can visit our website today. You can also download our app for easier access.

Ice is a solid substance, which is produced by the freezing of liquid water or water vapor. At temperatures down to 0°C, water vapor develops as frost at ground level and snowflakes (each consists of a single ice crystal) in the clouds. Below similar temperatures, liquid water produces a solid (solid ice), as, for example, sea ice, river ice, hail, and ice formed commercially or in the household refrigerators.

Occurrence

Ice occurs on the continents of Earth and the surface waters in various forms. Most notable are given as the continental glaciers (which are the ice sheets) that cover much of Greenland and Antarctica. Fewer masses of perennial ice, known as ice caps, occupy parts of Arctic Canada, including other high-latitude regions, whereas the mountain glaciers occur in more restricted areas, such as the flatlands below and mountain valleys. For more information on ice and its various forms, we can get it from many articles about ice.

The other occurrences of ice on the land are various types of ground ice, which are associated with permafrost, i.e., the permanently frozen soil common to most cold regions. In the polar regions of the oceanic waters, icebergs take palace when large masses of ice break off from ice shelves or glaciers and drift away. The seawater freezing in these regions results in the sheet formation of sea ice called pack ice.

During the winter season, similar ice bodies produce on rivers and lakes in several global locations. Ice in rivers and lakes, icebergs, glaciers, pack ice, and permafrost are treated separately. We can also know the detailed information on the widespread occurrences of glacial ice during the Earth’s past from various sources.

Structure of Ice

Ice or solid water is described as the solid-state of water (solid ice), which is a normally liquid substance that freezes to a solid-state (or solid state of water) at a temperature of 0 °C or below and expands to the gaseous state at a temperature of 100 °C or higher. Water is defined as a remarkable substance that is anomalous in virtually all of its physical and chemical properties and is literally the most complex of all the known single-chemical compounds.

The three-dimensional configuration of a water molecule can be visualised as a tetrahedron, with an oxygen nucleus in the centre and four legs with the possibility of a high electron. The two legs where the hydrogen nuclei are present are known as bonding orbitals.

Structure in Various Stages

In the liquid state, most of the water molecules are associated with a polymeric structure, which means molecule chains are connected by weak hydrogen bonds. Under the thermal agitation influence, there is a constant reforming and breaking of these bonds.

In the gaseous state, whether water vapor or steam, water molecules are largely independent of each other, and, apart from the collisions, their interactions are slight. Then, Gaseous water is largely monomeric, which it means, consisting of single molecules, although they rarely occur as dimers (union of two molecules), and even some trimmers (a combination of three molecules).

At the other extreme, in the solid-state, water molecules will interact with each other strongly enough to produce an ordered crystalline structure, with every oxygen atom collecting the four nearest of its neighbors and arranging them in a rigid lattice about itself.

The Ice Crystal

At standard atmospheric temperatures near 0 °C and pressure, commonly, the ice crystal takes the form of planes or sheets of oxygen atoms joined in an open hexagonal ring series. The axis, which is parallel to the hexagonal rings, is named the c-axis and coincides with the optical axis of the crystal structure.

Properties

Mechanical Properties

Like other crystalline solids, ice subject to stress undergoes elastic deformation, returning to its original shape when it is ceased by stress. However, if a shear force or stress is applied to a sample of ice for a very long time, first, the sample will deform elastically and will then continue to plastically deform, with a permanent shape alteration.

Optical Properties

Pure ice is very transparent, but air bubbles render it opaque somewhat. The absorption coefficient or the rate at which the incident radiation decreases with a depth of 0.1 cm-1 for snow and only 0.001 cm-1 or less than that for clear ice. Ice is doubly refracting, or weakly birefringent, which ensures the light is absorbed at different rates in different crystallographic directions.

Electromagnetic Properties

The albedo, or reflectivity, of solar radiation, which varies from 0.5 to 0.9 for snow, 0.15 to 0.35 for firn, and 0.3 to 0.65 for glacier ice (a 0 albedo means no reflectivity). Ice and snow are nearly completely “black” (absorbent) at thermal infrared wavelengths, with an albedo of less than 0.01. It means that ice and snow can either radiate or absorb long-wavelength radiation with high efficiency.

What is an Integrated Rate Equation Mean?

An equation that represents the dependence of the reaction rate on the concentration of reacting species is called the differential rate equation. The instantaneous rate of reaction can be expressed as the tangent slope at any instant of time in the graph of concentration-time type. Therefore, it is more difficult to define the rate of reaction from the concentration-time graph. Hence, we integrate the differential rate equation to get a relation between the rate constant and the concentration at various points. This resultant equation is called the integrated rate equation. For different order reactions, we can notice different integrated rate equations.

Integrated Rate Law for a Zero-order Reaction

In a zero-order reaction, the rate of reaction completely depends upon the zeroth power of the concentration of reactants. The zero-order reactions are noticed very rarely. A few examples of zero-order reactions can be given as decomposition of gaseous ammonia on a hot platinum surface, thermal decomposition of HI on a gold surface, and more. A general equation for a zero-order reaction including the rate constant k is derived below.

A → B

Rate is given by = – [frac{d[A]}{d}] = k[A]⁰ 

⇒ – [frac{d[A]}{d}] = k

⇒ – d[A] = -k dt

Integrating on both sides, we get:

⇒ [A] = – kt + c – (1)

Where c is given as the constant of integration,

At time t=0, [A] = [A]₀

Substituting the limits in equation (1) we get the value of c as follows,

⇒ [A]₀ = c

Using the resultant value of c in the equation (1), we get as follows,

⇒ [A] = – kt + [A]₀ 

The above-derived equation is referred to as an integrated rate equation for the zero-order reactions. We can also observe the above equation as a straight line with the concentration of reactant on the y-axis and time on the x-axis. And, the slope of the straight line signifies the value of the rate constant, k.

Integrated Rate Law for a First-order Reaction

In the first-order reaction, the rate of reaction depends on the first power of the reactant’s concentration. Artificial and Natural radioactive decay of the unstable nuclei is a few examples of the first-order reaction. A general equation for a first-order reaction including the rate constant k is derived below:

A → B

Rate is given by = – [frac{d[A]}{dt}] = k[A]  

⇒ [frac{d[A]}{[A]}] = – k dt

Integrating on both sides:

⇒ ln[A] = – kt + c —-(2)

Where c is given as the constant of integration,

At time t=0,  [A] = [A]₀

Substituting the limits in equation (2) we get the value of c, as given below.

⇒ ln[A]₀ = c

By using the value of c in the above equation we get,

⇒ ln[A] = – kt + ln [A]₀

We can notice that the above-derived equation can be plotted as a straight line including the ln[A] on the y-axis and time (t) on the x-axis. The negative slope of this straight line provides us with the value of the rate constant, k.

We can also define the value of the rate constant, k from the above-given equation as:

ln [frac{[A]}{[A]_{0}}] = -kt

⇒ k = – [frac{lnfrac{[A]}{[A]_{0}}}{t}]

So, the concentration at any time moment can be given as,

[A] = [A]0[^{e^{-kt}}]

Hence, we can now define the concentration and the rate of reaction at any moment by the help of the integrated rate equation for zero and the first-order reaction.

Integrated Rate Law

The mathematical relationship of the reaction rate including reactant concentrations is referred to as the rate law. This relationship can rely more heavily on the concentration of one specific reactant, whereas, the resulting rate law can include either none, some, or all of the reactant species that are involved in the reaction.

Consider the following hypothetical reaction:

a A + b B → c C

For this, the rate law can be expressed as:

Rate = k[A]y[B]z

Here, ‘k’ is The proportionality constant, which is known as the rate constant and also specific for the reaction, represented at a specific temperature. And, the rate constant changes with the temperature, whereas, its units depends on the sum of the concentration term exponents present in the rate law. The exponents of y and z must be experimentally determined and they do not correspond require mentally to the coefficients in the balanced chemical equation.

Factors Affecting the Rate of Reaction

There are primarily 5 factors that affect the rate of reaction, which are listed as follows:

For a reaction to take place/occur, as per the Collision Theory, the collisions between the 2 molecules of the 2 various mixtures must possess a degree of energy, which is called the ACTIVATION ENERGY. Only when the energy reaches this threshold can new bonds be formed after their original bonds have been broken.

Ionization can be defined as when a neutral atom or molecule can be converted into electrically charged atoms by gaining or losing a free electron. Ionization happens during the process of a chemical reaction. To ionize an atom or a molecule, either loses or gains electrons―the electron which is either gained or lost forms an ion. 

The atom or molecule that gains an electron becomes negatively charged and is called the anion. On the other hand, the atom or molecule that loses a free electron becomes positively charged and is called the cation. In the process of ionization, energy is either released or gained.

Ionization Energy and Formation of Ions

In the process of ionization, when an atom gains an electron, it forms a negatively charged ion called an anion. In this process, there is a loss or release of energy. The energy so lost is called electron affinity. It is often observed that atoms with enormous electron affinity tend to gain electrons and form negatively charged ions. 

Similarly, to ionize, if an atom loses an electron, it forms a positively charged ion called a cation. In the process of electron loss,  a large amount of energy is absorbed. The energy so absorbed by the atom is called ionization energy. The ionization energy is the energy required to remove the electron from the orbit of the atom. It becomes easier to remove electrons from atoms with a minimal amount of ionization energy. 

In the periodic table, metals carry a small amount of ionization energy, and alkali metals have the lowest ionization energy. Hence, alkali metals are mostly found as positively charged ions in different chemical compounds. For example, we can find sodium cation, i.e. Na+ in sodium chloride (NaCl).

Electron Ionization

Electron Ionization, formerly known as Electron Impact Ionization, is an ionization technique in which energetic electrons are made to react with solids and gases to produce ions. It is also known as Electron Bombardment Ionization. The electron impact ionization was the first known technique of mass spectrometry. However, this method of ionization is still prevalent. 

The electron ionization technique is considered one of the most challenging techniques of ionization. The reason behind this is electron impact ionization uses highly energetic electrons to produce ions. The method is advantageous in the determination of the structure of unknown compounds. The technique also serves as a medium in detecting various other thermally stable and volatile compounds in solids, liquids and gases. 

Plasma Ionization

A plasma is simply an ionized gas. When a gas is put under high temperatures, the electrons are stripped away from the atoms of the gas, and thus it forms plasma. For ionization of plasma, high temperatures are required, and the gas is pumped with energy to allow the electron to move freely to form ions. The best example of plasma ionization can be the sun’s corona, where the Hydrogen gas reacts under high temperature to form a hydrogen ion and a free electron.

H  → H⁺ + e^– .

Ionization of Acids and Bases

Acids ionize in water. Strong acids can completely ionize in water, whereas weak acids can only ionize partially. The degree of ionization of acid can determine its strength. This method is also known as percent ionization. The method determines the extent to which an acid ionizes in water. If an acid ionizes completely, it is tagged as a strong acid, and if it ionizes partially, it can be termed as a weak acid.

In a similar way, bases ionize in an aqueous solution to produce hydroxide ions. The bases that dissociate entirely in solutions are called strong bases. On the other hand, the bases that don’t completely dissociate in an aqueous solution are called weak bases. Percent ionization is used to identify the strength of bases also.

Ionization of Water 

The ionization of water or self-ionization of water is an ionization process in which a water molecule, either in pure water or aqueous solution, ionizes itself to produce ions. The following equation can explain the self-ionization of water:

H₂O  ⇄  H₃O⁺  +  OH^–.

In the above reaction, the water molecule dissociates to form a hydronium ion and a hydroxide ion. 

Exchange of heat is an important characteristic to note down in the fields of chemistry and thermal engineering. Considering the significance of this process, we are going to learn about a chemical procedure called isothermal expansion. After reading through this context, we will be able to know how the work done in an isothermal process is different in a reversible and irreversible state, and how heat gets transferred to another medium, along with important formulas and other pointers of study. 

But before everything, let us first quickly grasp the isothermal process definition along with 2 important gas forms namely ‘Real’ and ‘Ideal’ in brief.

Isothermal Expansion

To gain basic knowledge about the isothermal expansion of an ideal gas and real, it is essential to know what both these gases mean. 

An ideal gas possesses atoms and molecules that are highly elastic. Since the molecules of an ideal gas move faster than any other source, there is an absence of any intermolecular force of attraction between the elements. Moreover, the atoms and molecules in an ideal gas are present quite far away (distantly) and hence interaction is not possible at all. 

Also, ideal gases have their heat stored in the form of kinetic energy within each particle. This change in the internal energy leads to the change in the temperature, thus resulting in what exchange.  Helium is a classic example to state as an ideal gas.

Note that an ideal gas, under a certain reasonable tolerance condition, can change its medium into a real gas. 

On the other hand, when a gaseous element has a minimal level of intermolecular attractive forces between their molecules and atoms, then it can be termed as real gas. In the case of an ideal gas, it cannot exist and thrive naturally in the ecosystem. But, real gases can ideally act in both high-temperature conditions as well as in low-pressure situations. The common examples for a real gas include nitrogen (N), Helium (He), Oxygen (O), and more. 

Now, let’s move onto the topic of the isothermal expansion process. An isothermal process is defined by the change in a particular system where the temperature will remain constant. To be more precise, isothermal expansion gives ∆T = 0 (no change in the temperature).

When the vacuum gets expanded, it leads to the free expansion of a gas. In the case of an ideal gas, the rate of free expansion is NIL, that is, the work done is 0. The value of 0 is the result regardless of whether the process is irreversible or reversible. 

Some of the reversible cases of isothermal expansion include converting ice from its solid-state to the liquid state as water, dehydrogenation and hydrogenation in milling a chemical and more. Examples for an irreversible condition include work that is done against the friction, Joule’s heating effect, magnetic hysteresis and so on. 

P-V Diagram to Represent Isothermal Process

When a system has its internal energy changed, then it is given by the following condition:

∆U = q + w –(1)

Check out the keys to the formula below.

• ‘∆U’ to represent a change in internal energy.

• ‘q’ is labelled to denote the heat given by that respective system. 

• ‘w’ is the specific amount of work done over the system.

The following cases are given as isothermal process examples and types….

∆U = q + pex  ∆V

w = pex ∆V is the method to denote a work done in the condition of vacuum, Hence, the equation denoted as 1 (from the top) can also be represented as:

∆U = q + pex  ∆V

Moving on, if the volume in the condition is 0, therefore…

∆V = 0  → ∆U = q + pex ∆V 

∆U is the work done in this NIL vacuum condition. This also results in the fact that ∆U = Q. ‘qv’ is used to symbolize that the volume i.e. getting heat supplied at a constant rate.

Let us consider one more instance where an ideal gas like Helium (He) is subjected to isothermal expansion in the presence of vacuum (∆T = 0). Here, the work done for this vacuum will be NIL, that is w = 0 since the pex=0. According to the experiments of Joule, q =0 and therefore it is concluded that work done is NIL that is ∆U = 0.

Lastly, take this formula: ∆U = q + w. Now, we can express this statement for both reversible and irreversible isothermal expansions processes with the pointers given below: 

• Isothermal reaction for a reversible change is mentioned as q = -w = pex (Vf-Vi)

• Isothermal reaction for an irreversible change is given by q = -w = nRTln (Vf/Vi) = 2.303 nRT log (Vf/Vi)

• For in the case of an Adiabatic change, it is written as Q =0, ∆U = wad

Remember that the work done in an isothermal process of expansion for any given gas and vacuum condition is to be denoted as T = Constant, ∆T = 0 and dT = 0.