7) If one pound of water is at a temperature of 32 degrees Fahrenheit, how many BTU's must be removed in order to create a block of ice at 17 degrees? (A) 144 (B) 7.5 (C) 169 (D) 151.5

To determine the total British Thermal Units (BTUs) that must be removed to convert one pound of water at 32°F to ice at 17°F, follow these steps: 1. **Freeze the Water:** - The latent heat of fusion for water (the energy required to convert water to ice without changing its temperature) is approximately **144 BTU per pound**. 2. **Cool the Ice:** - After freezing, the ice needs to be cooled from 32°F to 17°F. - The specific heat capacity of ice is about **0.5 BTU/(lb·°F)**. - The temperature change is \(32°F - 17°F = 15°F\). - Energy removed to cool the ice: \(0.5 \times 15 = 7.5 \text{ BTU}\). 3. **Total BTUs Removed:** - **144 BTU** (for freezing) + **7.5 BTU** (for cooling) = **151.5 BTU**. **Answer:** (D) 151.5