Engineering Questions with Answers - Multiple Choice Questions

# MCQs on First Law of Thermodynamics

1 - Question

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

c
Explanation: 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 - Question

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

d
Explanation: 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 - Question

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

c
Explanation: 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 - Question

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

b
Explanation: 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 - Question

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

c
Explanation: 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 - Question

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

a
Explanation: 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 - Question

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

a
Explanation: 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 - Question

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

c
Explanation: 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 - Question

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

d
Explanation: 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 - Question

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