Question

A gas absorbs \( 100 \, \text{J} \) of heat while performing \( 40 \, \text{J} \) of work on its surroundings. Calculate the change in internal energy of the gas.

• A. \( 60 \, \text{J} \)
• B. \( 140 \, \text{J} \)
• C. \( 40 \, \text{J} \)
• D. \( 100 \, \text{J} \)

Hint:

When using the first law of thermodynamics, remember that work done by the system on the surroundings is considered positive, while heat absorbed by the system is also positive.

Answer 1

The Correct Option is A

The first law of thermodynamics defines the change in internal energy \( \Delta U \) as: \[ \Delta U = Q - W \] With \( Q = 100 \, \text{J} \) representing heat absorbed by the gas and \( W = 40 \, \text{J} \) representing work done by the gas on its surroundings. The calculation is as follows: \[ \Delta U = 100 - 40 = 60 \, \text{J} \] Consequently, the gas's internal energy change is \( 60 \, \text{J} \).