Question

Five hundred joules of heat are added to a closed system. The initial internal energy of the system is 87 J, and the final internal energy is 134 J. How much work is being done by the system?

Answer 1

Answer: W = 453J

Explanation: using first law of thermodynamics

∆U = Q - W

Where

Q= heat added

W = work done

∆U = internal energy

Also ∆U = Uf - UI

=134 -87

= 47J

Therefore work done will be

W = Q- ∆U

= 500 - 47

= 453J

Answer 2

We can solve the problem by using the first law of thermodynamics:

$\Delta U= Q-W$

where

$\Delta U$ is the variation of internal energy of the system

Q is the heat added to the system

W is the work done by the system

In this problem, the variation of internal energy of the system is

$\Delta U=U_f-U_i=134 J-87 J=47 J$

While the heat added to the system is

$Q=500 J$

therefore, the work done by the system is

$W=Q-\Delta U=500 J-47 J=453 J$