[Physics Class Notes] on Dalton's Law Pdf for Exam

Dalton’s law of partial pressure first published by John Dalton in the year 1802 states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures exerted by each individual gas present in the mixture. Eg: the total pressure exerted in a mixture of two gases is equal to the sum of the individual partial pressures exerted by each of the gas. In simple words, it can be stated that it is a mixture of two or more non-reacting gases, the total pressure is equal to the sum of the partial pressures of the non-reacting gases. In this topic, we have discussed what is dalton’s law, let us state dalton’s law of partial pressure with some examples. Let us suppose we have two mixture of gases A and B, so Dalton’s gas law states that the total pressure exerted by a mixture of two gases A and B is equal to the sum of the individual partial pressures exerted by both gas A and gas B as shown below:

Dalton’s Law Formula

For a mixture containing n number of gases the total pressure can be given as:

p[_{total}] = [sum_{i=1}^{n}] p[_{i}]

Or simply it can be written as:

p[_{total}] = p[_{1}] + p[_{2}] + p[_{3}] + p[_{4}] + p[_{5}] …. + p[_{n}]

Where P_total denotes total pressure exerted by the mixture of gases

and p1, p2,…, pn denotes the partial pressures of the gases 1, 2,…, ‘n’ in the mixture.

Expressing Partial Pressures in Terms of Mole Fraction

The mole fraction of a specific gas in a mixture of gases can be defined as the ratio of the partial pressure of that gas to the total pressure exerted by the gaseous mixture. This mole fraction is used to calculate the total number of moles of a constituent gas when the total number of moles in the mixture is known. Also, the volume occupied by a specific gas in a mixture can be calculated with the mole fraction formula with the help of the given equation.

X[_{i}] = P[_{i}] / P[_{total}] = V[_{i}] / V[_{total}] = n[_{i}] / n[_{total}]

Here X[_{i}] denotes the mole fraction of a gas ‘i’ in a mixture of ‘n’ gases, ‘n’ denotes the number of moles, ‘P’ denotes the pressure, and ‘V’ denotes the volume of the mixture.

Use of Dalton’s law

Dalton’s law can be used to calculate the mixtures of gases and the pressure and volume of each gas.

Presently many industries use sophisticated software for calculating these parameters. Still, Dalton’s and Avogadro’s laws are the basis of all these technologies.

Dalton’s Law of Partial Pressure Explanation by an Example

If there is a mixture of nitrogen gas, helium gas, and argon gas we have to measure the pressure and it was assessed in 2 atm. Further, the specialist also confirmed that the pressure of nitrogen in the mixture is 0.8 atm and the pressure of helium is 0.5 atm. Calculate the pressure of argon gas in the given mixture?

Solution: In order to calculate the pressure we can use Dalton’s law formula given as:

p[_{total}] = p[_{1}] + p[_{2}] + p[_{3}] + p[_{4}] + p[_{5}] …. + p[_{n}]

Now we put all the given value in it and rearrange the formula:

p[_{total}] = p[_{nitrogen}] + p[_{helium}] + p[_{argon}] 

p[_{total}] = p[_{nitrogen}] – p[_{helium}] = p[_{argon}] 

p[_{argon}] = 2atm – 0.8atm – 0.5atm

p[_{argon}] = 0.7atm

Conclusion 

In this article, we have discussed Dalton’s law of partial pressure definition and the Uses of Dalton’s law, We have also learned how to express Partial pressure in terms of mole fraction along with an example. To understand this topic more clearly try to solve maximum numerical.