Q31 / 150 · MHT CET 2025 (21 Apr Shift 2) · Chemistry

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

  • A
    $-10 \mathrm{~kJ}$
  • B
    $-35 \mathrm{~kJ}$
  • Correct answer
    C
    $-15 \mathrm{~kJ}$
  • D
    $-25 \mathrm{~kJ}$

Solution

The First Law of Thermodynamics provides the relationship between internal energy, heat, and work: $\Delta U = q + w$.

Applying the standard sign convention, work done by the system is negative ($w = -25\,\mathrm{kJ}$), while heat absorbed by the system is positive ($q = 10\,\mathrm{kJ}$).

Substituting these values yields:

$\Delta U = 10 + (-25) = -15\,\mathrm{kJ}$

The change in internal energy is therefore $-15\,\mathrm{kJ}$.

Final Answer: C

Hence, the correct answer is option: 'C'.

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