Answer:
ΔU = 53 BTU
Explanation:
In thermodynamics we consider heat entering a system as positive and heat leaving as negative.
Also, work performed by the system is positive and work applied to the system is negative.
The total heat applied to the system is:
Q = 72 - 7 = 65 BTU
The work is:
L = 12 BTU
The first law of thermodynamics states that:
Q = L + ΔU
Where ΔU is the change in internal energy.
Rearranging:
ΔU = Q - L
ΔU = 65 - 12 = 53 BTU
