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 is expressed as:\[\Delta U = Q - W\]Where:- \( \Delta U \) represents the change in internal energy,- \( Q \) represents the heat transfer,- \( W \) represents the work done by the gas.Step 2: Substitute known valuesWe are given:- Work done \( W = 50 \, \text{kJ} \),- Change in internal energy \( \Delta U = -30 \, \text{kJ} \) (negative due to a decrease).Substituting these values into the first law:\[-30 = Q - 50\]Step 3: Solve for \( Q \)\[Q = -30 + 50 = 20 \, \text{kJ}\]Final Answer:\[\boxed{+20 \, \text{kJ}}\]