Question

The heat transfer in a cyclic process are 20 kJ, -28 kJ, -2 kJ and 40 kJ. Determine the total work for this cycle process.
1. 30 kJ
2. 45 kJ
3. 54 kJ
4. 40 kJ
5. 60 kJ

Answer 1

Correct Answer - Option 1 : 30 kJ

Concept:

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant. Energy can be transformed from one form to another but cannot be created or destroyed.

The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings

δQ = ΔU + δW

ΔU = δQ - δW

According to the First Law of thermodynamics, “For a closed system undergoing a cycle, net heat transfer is equal to network transfer.”

ΣQ = ΣW

Net work done = Net heat in the cycle

Calculation:

Given:

Q₁ = 20 kJ, Q₂ = - 28 kJ, Q₃ = - 2 kJ, Q₄ = 40 kJ

Net work done in the cycle = Net heat in the cycle

W_net = Q1 + Q2 + Q₃ +  Q4 

= 20 - 28 - 2 + 40

= 30 kJ

The total work for this cycle process is 30 kJ.