Question

A vessel contains helium, which expands at constant pressure when 15 kJ of heat is supplied to it. The work performed (in kJ) in the expansion will be ______.

• A. 6 KJ
• B. 12 KJ
• C. 4 KJ
• D. 9 KJ

Answer 1

Answer: (D)

9 KJ

Answer 2

Correct option is A)

The first law of thermodynamics gives us the relation:
q=ΔU+w
For constant pressure process,
q=nCp​ΔT
ΔU=nCv​ΔT
$\frac{ΔU}{q}$​=Cp​Cv​​=$\frac{1}{γ}$​
Helium is a monoatomic gas i.e γ=$\frac{5}{3}$​
ΔU=$\frac{1}{γ}$​q=$\frac{3}{5}$​×15kJ=9kJ