In the energy balance example, the heat gained by the water equals the heat lost by the refrigerant.

• A. True
• B. False
• C. They are greater
• D. They are independent

Answer: (A)

The key idea is conservation of energy in a closed heat-exchange system. When two substances exchange heat and the system is isolated from the surroundings (no heat leaks, no work), all the heat that the refrigerant loses must be gained by the water. So the heat gained by the water and the heat lost by the refrigerant have the same magnitude, just opposite directions in sign. That’s why the statement is true. If there were any heat loss to the environment or other energy transfers, the amounts wouldn’t match exactly.