Question

To an ideal triatomic gas $800$ cal heat energy is given at constant pressure. If vibrational mode is neglected, then energy used by gas in work done against surroundings is

• A. 200 cal
• B. 300 cal
• C. 400 cal
• D. 60 cal

Answer 1

Answer: (A)

Heat at constant pressure
$\Delta Q=n{C}_P\Delta T$
Heat for doing work
$\Delta W=nR\Delta T$
Then $\frac{\Delta W}{\Delta Q}=\frac{nR\Delta T}{n{C}_P\Delta T}$
$\frac{\Delta W}{800}=\left(\frac{\gamma -1}{\gamma }\right)$
$\frac{\Delta W}{800}=1-\frac{1}{\gamma }$
$\frac{\Delta W}{800}=1-\frac{3}{4}$
$\Delta W=200cal$