Question

The change in internal energy of a system that has absorbed $2\text{kcal}$ of heat and does $500\text{J}$ of work is

• A. $6400\text{J}$
• B. $5400\text{J}$
• C. $7860\text{J}$
• D. $8900\text{J}$

Answer 1

The correct option is C $7860\text{J}$

Heat absorbed by the system $\left(\Delta Q\right)=2\text{k cal}=2\times {10}^3\times 4.18=+8360\text{Joules}$
Work done by the system $\left(\Delta W\right)=+500\text{J}$
According to First law of Thermodynamics
$\Delta Q=\Delta U+\Delta W$
Substituting the given values we get,
$8360=\Delta U+500\Rightarrow \Delta U=7860\text{J}$
Thus, option (c) is the correct answer.