Question

When a system absorbs 8 kJ of heat and does 2.2 kJ of work on surroundings, calculate the internal energy change.

• A. -10.2 kJ
• B. 10.8 kJ
• C. 8.0 kJ
• D. 5.8 kJ

Hint:

The change in internal energy \(\Delta U\) is given by the equation \(\Delta U = Q - W\), where \(Q\) is the heat absorbed and \(W\) is the work done by the system.

Answer 1

The Correct Option is D

Step 1: Understanding the first law of thermodynamics.
The first law of thermodynamics states that the change in internal energy \(\Delta U\) is equal to the heat absorbed by the system \(Q\) minus the work done by the system \(W\). The equation is: \[ \Delta U = Q - W \] Given: Heat absorbed \(Q = 8 \, \text{kJ}\) Work done on surroundings \(W = 2.2 \, \text{kJ}\) (work done by the system is positive)

Step 2: Calculation.
\[ \Delta U = 8.0 \, \text{kJ} - 2.2 \, \text{kJ} = 5.8 \, \text{kJ} \]
Step 3: Conclusion.
The internal energy change is \(\Delta U = 5.8 \, \text{kJ}\), so the correct answer is (D) 5.8 kJ.