Question

The internal energy change in a system that has absorbed $2Kcal$ of heat and done $500J$ of work is

• A. $8900J$
• B. $6400J$
• C. $5400J$
• D. $7900J$

Answer 1

Answer: (D)

$7900J$

Given: Heat absorbed = 2 Kcal

work done = 500 J

Solution: As we know, according to the law of thermodynamics

$△U=Q-W$ (1)

where, U is the change in the internal energy,

Q denotes the heat given to the system and

W denotes the work done by the system.

Also, $1cal=4.2J$

So, $2Kcal=2\times 1000\times 4.2$

Substituting the values in equation (1) we get,

$△U=2\times 1000\times 4.2-500$

$△U=7900J$

Hence, the correct option is (D).