Question

A gas is at $1atm$ pressure with a volume $800c{m}^3$. When $100J$ of heat is supplied to the gas, it expands to $1L$ at constant pressure. The change in its internal energy is

• A. $80J$
• B. $-80J$
• C. $20J$
• D. $-20J$

Answer 1

Answer: (A)

$80J$

The work done on the gas at constant pressure is,
$W=P\Delta V$
Thus, W = $1\times (1-0.8)$
$W=0.2atm-L=20J$
Now, heat supplied, $Q=100J$
According to the first law of thermodynamics,
Q = U + W
Thus, $U=100-20=80J$