Question

A systems initial internal energy is 27 J. Then heat is added to the system. If the final
internal energy is 34 J and the system does 24 J of work, how much heat is added to
the system?​

Answer 1

Answer

Solution:- (C) −10J

As the heat is given to the system and work is done by the system, therefore,

q=+10J

W=−20J

Now from the first law of thermodynamics,

ΔU=q+W

⇒ΔU=10+(−20)=−10J

Hence the change in internal enrgy is −10J.

Answer 2

Given:

Initial internal energy = 27 J

Final internal energy = 34 J

Work done by the system = 24 J

To find:

Amount of heat added to the system.

Solution:

Let,

U1 = Initial internal energy = 27 J

U2 = Final internal energy = 34 J

W = Work done by the system = 24 J ( Work is done by the system so it will be positive)

Q = Heat added to the system ( Q will be positive as heat is added to  the system.)

Change in internal  energy will be

U2 - U1 = 34 - 27

ΔU = 7 J

Now, we know that

ΔU = Q - W

Q = ΔU + W

Q = 7 + 24

Q = 31 J

Heat added to the system will be 31 J.