Question

Calculate the change in internal energy of the system if 25 kJ of work is done by the system and it absorbs 10 kJ of heat.

• A. -10 kJ
• B. -35 kJ
• C. -15 kJ
• D. -25 kJ

Hint:

The change in internal energy can be calculated using the first law of thermodynamics: \( \Delta U = Q - W \), where \( Q \) is heat absorbed and \( W \) is work done.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to apply the First Law of Thermodynamics, paying attention to the sign conventions for heat and work.
Step 2: Key Formula or Approach:
Formula: \( \Delta\text{U} = q + w \)
Sign conventions (IUPAC):
\( q = + \) (heat absorbed by system)
\( w = - \) (work done by system)
Step 3: Detailed Explanation:
Given:
Heat absorbed \( q = +10 \text{ kJ} \)
Work done by system \( w = -25 \text{ kJ} \)
Calculate \( \Delta\text{U} \):
\[ \Delta\text{U} = +10 \text{ kJ} + (-25 \text{ kJ}) \] \[ \Delta\text{U} = -15 \text{ kJ} \] Step 4: Final Answer:
The change in internal energy is \( -15 \text{ kJ} \).