Question

200 J of heat is added to a working substance. Internal energy is raised from 30 J to 70 J during the process. The amount of external work done is

• A. 40 J
• B. 100 J
• C. 130 J
• D. 160 J

Answer 1

Answer:

D. 160 J

Thermodynamic Principle

• The process is governed by the First Law of Thermodynamics, which is an expression of the Law of Conservation of Energy.

• The mathematical formulation is ΔQ = ΔU + ΔW, where:

  • ΔQ is the heat added to the system.

  • ΔU is the change in internal energy (U_final - U_initial).

  • ΔW is the external work done by the system.

Calculation Steps

1. Identify Given Values: Heat added (ΔQ) = 200 J; Initial internal energy (U_i) = 30 J; Final internal energy (U_f) = 70 J.

2. Calculate Change in Internal Energy (ΔU): ΔU = 70 J - 30 J = 40 J.

3. Apply the Formula: 200 J = 40 J + ΔW.

4. Solve for ΔW: ΔW = 200 J - 40 J = 160 J.