Question

a system absorbs 20kJ of heat and also does 10KJ of work. the net internal energy of the system

Answer 1

system absorb +20kj so work is done on system and work 10 kj on surrounding so net internal energy is 20-10=10kj

Answer 2

Answer: +10 kJ

Explanation: According to first law of thermodynamics:

$\Delta U=q+w$

$\Delta U$=Change in internal energy

q = heat absorbed or released

w = work done on or by the system

w = work done by the system=$-P\Delta V$  {Work is done by the system is negative as the final volume is greater than initial volume }

w = - 10 kJ

q = +20 kJ   {Heat absorbed by the system is positive}

$\Delta U=+20+(-10)=+10kJ$