Question

Determine which of the following sets of data satisfy the first law of thermodynamics? (Recall that E = total energy = U + KE + PE)

a. W = 50 kJ Q = 170 kJ DeltaE = 120 kJ

b. W = 100 Btu Q = -110 Btu DeltaE = -210 Btu

c. W = 250 kJ Q = -110 kJ DeltaE = -100 Wh

d. W = 44 kPa-m3   Q = -84 kPa-m3 DelatE = 40 kN-m

Answer 1

The first law of thermodynamics is an application of the law of conservation of energy which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. The first law can be formulated as ΔE = Q - W

a. ΔE = 120 kJ ; W = 50 kJ ; Q = 170 kJ

This set of data satisfies the 1st law.

b. ΔE = -210 Btu ; W = 100 Btu ; Q = -110 Btu

This set of data satisfies the 1st law.

c. ΔE = -100 Wh = -360 kJ ; W = 250 kJ ; Q = -110 kJ

This set of data satisfies the 1st law.

d. ΔE = 40 kN-m = 40 kPa-m³ ; W = 44 kPa-m³ ; Q = -84 kPa-m³

This set of data does not satisfy the 1st law.