250+ TOP MCQs on First Law of Thermodynamics and Answers

Fluid Mechanics Multiple Choice Questions on “First Law of Thermodynamics”.

1. First law of thermodynamics deals with _______
a) Conservation of mass
b) Conservation of momentum
c) Conservation of energy
d) Conservation of pressure

Answer: c
Clarification: First law corresponds to the law of conservation of energy. It states that energy can neither be created nor destroyed, but can be transformed from one form to the other. It follows the principle of heat transfer and energy transfer.

2. Equation of the first law of thermodynamics is ________
a) Internal Energy= Heat added into work done
b) Internal Energy= Heat rejected into work done
c) Internal Energy= Heat added divided by work done
d) Internal Energy=Heat added plus work done

Answer: d
Clarification: It is a thermodynamic expression which gives a relationship between internal energy, heat and work done. Work done on the system is positive, and work done by the system is negative. The standard unit of all these quantities is Joule.

3. During a fluid flow, the temperature is developed due to________
a) Increase in density
b) Change in pressure
c) Translational Kinetic Energy
d) Fluid level

Answer: c
Clarification: When there is a high rate of fluid flow, the molecules tend to collide with each other. At this state, the average translational kinetic energy of the particles increases. The temperature developed due to this is called as Kinetic temperature.

4. The equation for the average kinetic energy is_________
a) 0.5 KT
b) 1.5 KT
c) 2.5 KT
d) 3.5 KT

Answer: b
Clarification: The equation for kinetic energy is 0.5mv², where m= mass and v= velocity. This equation corresponds to 1.5 KT, where K=Boltzmann’s constant and R= Gas constant.

5. An increase in enthalpy leads to an increase in __________
a) Increase in pressure
b) Increase in volume
c) Increase in internal energy
d) Increase in mass

Answer: c
Clarification: When the temperature increases, the amount of molecular interactions also increases. Using the equation from the first law of thermodynamics, internal energy also increases with the increase in temperature. Thus, increase in enthalpy leads to an increase in internal energy.

6. Entropy occurs due to _______
a) Change in macroscopic variables
b) Volumetric changes only
c) Mass changes only
d) Temperature only

Answer: a
Clarification: Entropy is related to a number of microscopic configurations. It can have some of the most specified macroscopic variables. These macroscopic variables undergo changes, which lead to a disorder or randomness.

7. What is the equation of entropy?
a) Ratio of reversible transfer of heat to absolute temperature
b) Ratio of absolute temperature to reversible heat transfer
c) Ratio of adiabatic heat to macroscopic variables
d) Ratio of macroscopic variables to adiabatic heat

Answer: a
Clarification: This equation was defined by Rudolf Clausius, who defined entropy as a ratio of reversible heat transfer to that of its absolute temperature. This definition is also called the macroscopic definition of entropy.

8. SI unit of enthalpy is_______
a) Joule/kgK
b) Joule/K
c) Joule/kg
d) K/kg

Answer: c
Clarification: Enthalpy is defined as a measurement of energy in a thermodynamic system. It is equal to the internal energy plus the product of volume and pressure. Thus, giving a unit of Joule/kg.

9. Which among this is not an exothermic reaction?
a) Combustion reaction
b) Neutralization reaction
c) Thermite reaction
d) Evaporating liquid water

Answer: d
Clarification: Exothermic reaction is a reaction that releases energy by either light or heat. It is the opposite of endothermic reactions. In this case, evaporating liquid water is an endothermic reaction. Endothermic reaction is a reaction in which the system absorbs heat from its surroundings.

10. What reaction takes place during photosynthesis?
a) Exothermic reaction
b) Endothermic reaction
c) Redox reaction
d) Combustion reaction

Answer: b
Clarification: Photosynthesis takes place by absorbing heat and energy from the surroundings. Since, endothermic reaction is a reaction in which the system absorbs heat from its surroundings, the reaction that takes place during photosynthesis is an endothermic reaction.