# Thermodynamics Questions and Answers – Enthalpy

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Enthalpy”.

1. The enthalpy of a substance(denoted by h), is defined as
a) h=u-pv
b) h=u+pv
c) h=-u+pv
d) h=-u-pv

Explanation: This is a basic definition for enthalpy.

2. In a constant volume process, internal energy change is equal to
a) heat transferred
b) work done
c) zero
d) none of the mentioned

Explanation: In a constant volume process, there is no work other than the pdV work.

3. For an ideal gas, enthalpy becomes
a) h=u-RT
b) h=-u-RT
c) h=u+RT
d) h=-u+RT

Explanation: For an ideal gas, pv=RT.

4. Enthalpy is an intensive property of a system.
a) true
b) false

Explanation: Enthalpy is an intensive property measured mostly in kJ/kg.

5. Heat transferred at constant pressure _____ the enthalpy of a system.
a) decreases
b) increases
c) first decreases then increases
d) first increases then decreases

Explanation: At constant pressure, (dQ)=dh where h=u+pv is the specific enthalpy of the system.
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6. The enthalpy of an ideal gas depends only on the temperature.
a) true
b) false

Explanation: This is because the internal energy of an ideal gas depends only on the temperature.

7. Total enthalpy of a system H is given by
a) H=h/m
b) H=m/h
c) H=mh
d) none of the mentioned

Explanation: Total enthalpy equals (mass*enthalpy) of substance.

8. The enthalpy and internal energy are the function of temperature for
a) all gases
b) steam
c) water
d) ideal gas

Explanation: The enthalpy of an ideal gas depends only on the temperature because the internal energy of an ideal gas depends only on the temperature.

9. Change in enthalpy of a system is due to heat supplied at
a) constant volume
b) constant pressure
c) both at constant volume and pressure
d) none of the mentioned

Explanation: Change in enthalpy occurs when heat is given to a system at constant pressure.

10. At constant pressure
a) pdv=d(pv)
b) dQ=du+d(pv)
c) dQ=d(u+pv)
d) all of the mentioned

Explanation: For a constant pressure process, dQ=du+pdv.

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