Question

Gas contained in a closed system consisting of a piston-cylinder arrangement is expanded. Work done by the gas during expansion is 50 kJ. The decrease in internal energy of the gas during expansion is 30 kJ. The heat transfer during the process is equal to:

• A. -20 kJ
• B. +20 kJ
• C. -80 kJ
• D. +80 kJ

Hint:

For energy conservation, use the first law of thermodynamics to find heat transfer by knowing work and internal energy changes.

Answer 1

The Correct Option is B

Step 1: Apply the First Law of Thermodynamics
The first law of thermodynamics states: \[ \Delta U = Q - W \] Where: - \( \Delta U \) is the change in internal energy, - \( Q \) is the heat transfer, - \( W \) is the work done by the gas. Step 2: Substitute known values Given: - Work done \( W = 50 \, \text{kJ} \), - Decrease in internal energy \( \Delta U = -30 \, \text{kJ} \) (since it's a decrease, we take it as negative). Substitute into the equation: \[ -30 = Q - 50 \] Step 3: Solve for \( Q \) \[ Q = -30 + 50 = 20 \, \text{kJ} \] Final Answer: \[ \boxed{+20 \, \text{kJ}} \]