Question

A system absorbs $10$kJ of heat and does $4$ kJ of work. The internal energy of the system?

• A. increases by $6$kJ
• B. decreases by $6$kJ
• C. decreases by $14$kJ
• D. increases by $14$kJ

Answer 1

The correct option is A increases by $6$kJ

Solution:- (A) increases by $6kJ$

As given that work is done by the system and heat is absorbed by the system.

Therefore,

$q=10kJ$

$w=-4kJ$

Now from first law of thermodynamics,

$\Delta U=q+w$

$\Rightarrow \Delta U=10+(-4)=6kJ$

$\Rightarrow U_f-U_i=6\Rightarrow U_f=(U_i+6)$

Hence the internal energy is increased by $6kJ$.