Question

A system has absorbed $5\text{kcal}$ of heat and does $200\text{J}$ of work. The change in internal energy of the system is

• A. $20.8\text{J}$
• B. $20.8\text{kJ}$
• C. $208\text{J}$
• D. $2.08\text{kJ}$

Answer 1

The correct option is B $20.8\text{kJ}$

Given,
Heat absorbed by system $(+Q)=5\times {10}^3\times 4.2=21\times {10}^3\text{J}$
Work done by the system $(+W)=200\text{J}$
From, 1st law of thermodynamics,
$Q=\Delta U+W$
$\Rightarrow \Delta U=20.8\text{kJ}$