Question

Calculate the entropy for the melting of 25g of ice, initially stored at -15 degree celcius, then brought to 25 degree celcius. Consider the specific heat of melting for water to be 79.7 cal g-1, the heat capacity of ice is 0.5 cal g-1, and that of liquid water is 1.0 cal g-1

Answer 1

Question #62693, Chemistry / Physical Chemistry

Calculate the entropy for the melting of 25g of ice, initially stored at -15 degree celcius, then brought to 25 degree celcius. Consider the specific heat of melting for water to be 79.7 cal g-1, the heat capacity of ice is 0.5 cal g-1, and that of liquid water is 1.0 cal g-1

Answer:

$$Q = c m \Delta T$$

We have three stages:

1) Ice heat from -15 °C to 0 °C:

$$Q_{1} = 0.5 \frac{\text{cal}}{\text{g}} \times 25 \text{ g} \times (0 - (-15)) = 187.5 \text{ cal}$$

2) Ice melting at 0 °C:

$$Q_{2} = 79.7 \frac{\text{cal}}{\text{g}} \times 25 \text{ g} = 1992.5 \text{ cal}$$

3) Water heat from 0 °C to 25 °C:

$$Q_{3} = 1.0 \frac{\text{cal}}{\text{g}} \times 25 \text{ g} \times (25 - 0) = 625.0 \text{ cal}$$

Summary:

$$Q = Q_{1} + Q_{2} + Q_{3} = 187.5 + 1992.5 + 625.0 = 2805 \text{ cal}$$

2805 cal

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