# Thermodynamics Questions and Answers – Ideal Gas-2

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Ideal Gas-2”.

1. The value of cp and cv depend on
a) temperature of the gas
b) ɣ and R
c) pressure of the gas
d) all of the mentioned

Explanation: The value of cp and cv depends on the number of atoms in a molecule and the molecular weight of the gas.

2. Which of the following statement is true?
a) value of ɣ for monoatomic gases is 5/3
b) value of ɣ for diatomic gases is 7/5
c) for polyatomic gases, the value of ɣ is approximately taken as 4/3
d) all of the mentioned

Explanation: These values of ɣ can be shown by the classical kinetic theory of gases.

3. The maximum and minimum values of ɣ is
a) 1.33, 1
b) 2.00, 1
c) 1.67, 1
d) 1.25, 1

Explanation: ɣ=1 when cp=cv and ɣ=1.67=5/3 for monoatomic gases.

4. Which of the following equation can be used to compute the entropy change between any two states of an ideal gas?
a) s2-s1 = cv*ln(T2/T1) + R*ln(v2/v1)
b) s2-s1 = cp*ln(T2/T1) – R*ln(p2/p1)
c) s2-s1 = cp*ln(v2/v1) + cv*ln(p2/p1)
d) all of the mentioned

Explanation: Any of the given three equations can be used.

5. For a reversible adiabatic change, ds=0.
a) true
b) false

Explanation: For a reversible adiabatic process, change in entropy is zero.

6. For a reversible adiabatic process,
a) p*(v^ɣ) = constant
b) T*(v^(ɣ-1)) = constant
c) T*(p^(1-ɣ)/ɣ) = constant
d) all of the mentioned

Explanation: All these relations come from the pv=RT and p*(v^ɣ) = constant.

7. Which of the following is true for a polytropic process?
a) p(v^n) is used to describe the process
c) it can be reversible
d) all of the mentioned

Explanation: These are the properties of an adiabatic process.

8. In the equation p(v^n), n is calculated by
a) (logp1 + logp2) / (logv2 + logv1)
b) (logp1 – logp2) / (logv2 – logv1)
c) (logp1 – logp2) / (logv2 + logv1)
d) none of the mentioned

Explanation: It comes from the p1*(v1^n) = p2*(v2^n).

9. For entropy change in a polytropic process, which of the following statement is true?
a) when n=ɣ, the entropy change becomes zero
b) if p2>p1, for n<=ɣ, the entropy of the gas decreases
c) for n>ɣ, the entropy of the gas increases
d) all of the mentioned

Explanation: This comes from the relation s2-s1 = [(n-ɣ)/{n(ɣ-1)}]*R*ln(p2/p1).

10. Polytropic specific heat is given by cn=cv(ɣ-n)/(1-n) .
a) true
b) false

Explanation: The polytropic specific heat is used in the relation Qr=cn*ΔT.

11. Which of the following is true?
a) for n>ɣ, there will be positive heat transfer and gain in entropy
b) for n<ɣ, there will be negative heat transfer and decrease in entropy
c) both of the mentioned
d) none of the mentioned 