Question

In a thermodynamic process, the pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas is 30 J, the final internal energy will be:

• A. \(2 \text{ J}\)
• B. \(42 \text{ J}\)
• C. \(18 \text{ J}\)
• D. \(58 \text{ J}\)

Hint:

Carefully follow sign convention for heat and work in thermodynamics.

Answer 1

The Correct Option is C

Step 1: First law of thermodynamics: \[ \Delta U = Q - W \]
Step 2: Heat released: \(Q = -20 \text{ J}\) Work done on gas: \(W = -8 \text{ J}\)
Step 3: \[ \Delta U = -20 - (-8) = -12 \text{ J} \]
Step 4: \[ U_f = 30 - 12 = 18 \text{ J} \]