250+ TOP MCQs on Thermodynamics – Spontaneity and Answers

Chemistry MCQs for Class 11 on “Thermodynamics – Spontaneity”.

1. Which of the following is not a spontaneous process?
a) sugar dissolves in water
b) melting of iron
c) rusting of iron
d) evaporation of water
Answer: b
Clarification: A physical or chemical process which occurs by its on in a particular direction under a particular set of conditions without any force is known as a spontaneous process and it cannot be reversed. Here melting of iron is only possible when we supply a large amount of heat so it is not a spontaneous process.

2. Spontaneous reactions that occur or mostly ________in nature.
a) endothermic
b) exothermic
c) both endothermic and exothermic
d) neither exothermic nor endothermic
Answer: b
Clarification: All the processes which occur with a decrease of energy are exothermic in nature, those with change of enthalpy as negative occurs spontaneously. It is not true in case of some endothermic reactions, when they occur spontaneously.

3. Entropy increases for a spontaneous reaction.
a) true
b) false
Answer: a
Clarification: A process is spontaneous if and only if the entropy of Universe increases for a process to be spontaneous ΔS(universe) > 0. At equilibrium, ΔS = 0. Saudi about the statement that the Entropy increase for a spontaneous reaction is true.

4. Entropy is an ___________ property.
a) intensive
b) extensive
c) neither intensive or extensive
d) both intensive and extensive
Answer: b
Clarification: Entropy is a measurement of randomness or disorder of molecules it is a state function as well as an extensive property. Its units are J/K-mole. Extensive property depends on the size and quantity of the mass.

5. Which of the following relation is true between Gibbs energy, enthalpy, temperature, and entropy?
a) G = H -TS
b) G = H -T
c) G = H -S
d) G = -TS
Answer: a
Clarification: The energy that is available for a system at some conditions and by which useful work can be done is Gibbs free energy. The relation between Gibbs free energy, enthalpy, temperature and entropy is given by Gibbs Helmholtz equation; G = H -TS.

6. Reaction is spontaneous if Gibbs free energy is __________
a) greater than zero
b) equal to zero
c) less than zero
d) infinity
Answer: c
Clarification: A reaction is spontaneous if Gibbs free energy is less than zero and the reaction is nonspontaneous if the Gibbs free energy is greater than zero. The reaction is at equilibrium state if gives free energy is equal to zero.

7. If the enthalpy is positive and entropy is negative, what do you understand about Gibbs free energy?
a) it is positive
b) negative
c) may be negative
d) may be positive
Answer: a
Clarification: According to the Helmholtz equation; G = H -TS, when enthalpy H is positive and entropy S is negative, the Gibbs free energy is always positive and the reaction is not spontaneous at all temperatures.

8. The entropy of the universe is always increasing is ____________
a) zeroth law of thermodynamics
b) first law of thermodynamics
c) second law of thermodynamics
d) third law of thermodynamics
Answer: b
Clarification: The second law of thermodynamics is given as the entropy of the universe is always increasing in the course of every spontaneous or natural change also can be said as the heat cannot flow itself from a colder to a hotter body.

9. Third law of thermodynamics is only applicable for perfectly crystalline substances.
a) true
b) false
Answer: a
Clarification: We can define the third law of thermodynamics entropy of a perfectly crystalline substance at zero kelvin or absolute zero is taken to be zero, but this is not applicable if there is any Imperfection at 0 k, the entropy will be larger than 0.

10. ΔS(universe) > 0 can also be written as _________
a) ΔS(system) + ΔS(surroundings) > 0
b) ΔS(surroundings) > 0
c) ΔS(system)
d) ΔS(system) – ΔS(surroundings) > 0
Answer: a
Clarification: ΔS(universe) > 0 can also be written as ΔS(system) + ΔS(surroundings) > 0, as the universe is nothing but the system and surroundings. The above mentioned condition is used when a reaction is at equilibrium.

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