Question

A sample of ideal gas $(\gamma =1.4)$ is heated at constant pressure. If an amount of $85J$ of heat is supplied to gas, find $△U$

• A. $30.5J$
• B. $60.7J$
• C. $50.5J$
• D. $70J$

Answer 1

The correct option is B $60.7J$

Heat supplied at constant pressure is given as :
$q_p=△H=n{C}_p△T$ ........eq(1)
and $q_p=△H=85J$

we know $\gamma =\frac{C_p}{C_v}$
$C_p=\gamma C_v$
putting in eq.(1)
$85=n\gamma C_v△T$
$85=1.4n{C}_v△T$ .....eq(2)

now we need to find $△U$ which is equal to
$△U=n{C}_v△T$
from eq.(2)
$△U=\frac{85}{1.4}=60.7J$