Question

Calculate the change in internal energy of the system if work done by the system is 18 joule and absorbs heat 50 joule in a particular reaction.

• A. 20 J
• B. 32 J
• C. 48 J
• D. 68 J

Hint:

Sign Convention Rule: Anything going INTO the system (absorbing heat, getting compressed by outside work) is POSITIVE. Anything coming OUT of the system (releasing heat, expanding against the surroundings) is NEGATIVE!

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The first law of thermodynamics states that the change in internal energy ($\Delta U$) is the heat added to the system minus the work done by the system.

Step 2: Formula Application:
$\Delta U = q + w$ (using the IUPAC sign convention where $w$ is positive if work is done on the system).

Step 3: Explanation:
- Heat absorbed ($q$) = +50 J. - Work done by the system = 18 J (so $w = -18$ J in IUPAC convention). $\Delta U = 50 + (-18) = 32$ J.

Step 4: Final Answer:
The change in internal energy is 32 J.