For solar energy to be effective, collected heat must be...

For solar energy to be effective, collected heat must be stored for use during periods of decreased sunshine. One proposal suggests that heat can be stored by melting solids that, upon solidification, would release the heat. Calculate the heat that could be stored by melting 1000 kg of each of the following solids. (Note: The water in each formula is included in the molecular weight.) a. Calcium chloride $\left(\mathrm{CaCl}_2 \cdot 6 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=30.2^{\circ} \mathrm{C}$, heat of fusion $=40.7 \mathrm{cal} / \mathrm{g}$ b. Lithium nitrate $\left(\mathrm{LiNO}_3 \cdot 3 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=29.9^{\circ} \mathrm{C}$, heat of fusion $=70.7 \mathrm{cal} / \mathrm{g}$ c. Sodium sulfate $\left(\mathrm{Na}_2 \mathrm{SO}_4 \cdot 10 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=32.4^{\circ} \mathrm{C}$, heat of fusion $=57.1 \mathrm{cal} / \mathrm{g}$

For solar energy to be effective, collected heat must be stored for use during periods of decreased sunshine. One proposal suggests that heat can be stored by melting solids that, upon solidification, would release the heat. Calculate the heat that could be stored by melting 1000 kg of each of the following solids. (Note: The water in each formula is included in the molecular weight.)
a. Calcium chloride $\left(\mathrm{CaCl}_2 \cdot 6 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=30.2^{\circ} \mathrm{C}$, heat of fusion $=40.7 \mathrm{cal} / \mathrm{g}$
b. Lithium nitrate $\left(\mathrm{LiNO}_3 \cdot 3 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=29.9^{\circ} \mathrm{C}$, heat of fusion $=70.7 \mathrm{cal} / \mathrm{g}$
c. Sodium sulfate $\left(\mathrm{Na}_2 \mathrm{SO}_4 \cdot 10 \mathrm{H}_2 \mathrm{O}\right)$ : melting point $=32.4^{\circ} \mathrm{C}$, heat of fusion $=57.1 \mathrm{cal} / \mathrm{g}$

Key Concepts

Mass-Energy Calculations

These calculations involve multiplying the mass of the material by its heat of fusion (energy per unit mass required for phase change) to determine the total energy that can be stored or released during the melting or freezing process. Such calculations are fundamental to evaluating and comparing the effectiveness of different materials for thermal energy storage applications.

Thermal Energy Storage

Thermal energy storage involves capturing heat energy for later use, which is particularly important in systems like solar energy applications where the availability of sunlight varies over time. Using phase change materials as a storage medium leverages the latent heat of fusion to store a concentrated amount of energy during the day and release it at night or during low sunlight periods.

Phase Change Materials

Phase change materials (PCMs) are substances that absorb or release significant amounts of latent heat during their phase transitions. In the context of solar energy systems, PCMs can store heat when they melt and release it upon solidification, providing a method for efficient thermal energy storage, especially during periods when solar radiation is unavailable.

Latent Heat of Fusion

This refers to the amount of energy required to change a unit mass of a substance from a solid to a liquid state at its melting point without changing its temperature. It is a crucial property for phase change materials used in thermal energy storage, because it indicates how much energy can be stored or released during the melting or solidification process.

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