Question

A system conducts 120 cal of heat to the surroundings while delivering 254 cal of work. What is the change in internal energy of the system (in kJ, mind the signs of these energy terms )?

(a) ‒1.56 kJ

(b) ‒0.561 kJ

(c) ‒0.0894kJ

(d) 0.561 kJ

(e) 1.56 kJ

Answer 1

According to Thermodynamics rules

When system absorbs heat then Q is +ve

When work is done on the system the W is +ve

So Using first law of Thermodynamics

Given heat is conducted by system to surrounding so Q = -120 cal

Also work done by system = W= -254 cal

So change in internal energy is given by

Also we know

1 cal =4.18 Joules

So

Option a is correct