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Phase change refers to the transformation of a substance from one state of matter to another. Ethyl alcohol can exist as a solid, liquid, or gas and each transition between these phases involves energy changes.

For example, when ethyl alcohol changes from a gas to a liquid, it undergoes condensation. This process occurs at its boiling point of around \(78.0^{\circ}C\). Energy, in the form of heat, is removed from the substance, allowing the molecules to come closer and form the liquid phase. The key term here is the "heat of vaporization" (\(L_v\)), which is the amount of energy needed to convert 1 kg of a substance from liquid to gas or vice versa. In our case, ethyl alcohol has a heat of vaporization of \(879 \, \text{kJ/kg}\).

Similarly, when the substance changes from liquid to solid, it goes through freezing, which happens at ethyl alcohol's freezing point, \(-114^{\circ}C\). The "heat of fusion" (\(L_f\)) is the energy required to change 1 kg of a substance from solid to liquid or vice versa, and for ethyl alcohol, it's \(109 \, \text{kJ/kg}\). Knowing these properties helps us calculate how much energy needs to be removed during phase changes.

Heat transfer is a fundamental principle responsible for the phase changes of substances. It's the process by which heat energy is transported from one area to another, often resulting in a phase change. This movement of heat happens due to the temperature difference between substances or within a substance.

In the case of ethyl alcohol, several heat transfer processes occur when going from a gas at \(78.0^{\circ}C\) to a solid at \(-114^{\circ}C\). By removing heat, we cause the liquid molecules to lose energy and slow down enough to transition into the solid phase.

Heat transfer calculations involve specific formulas like the heat equation for condensation:

• \( Q = m \times L_v \)

Likewise, we calculate the heat transfer needed to cool the substance as it stays in one phase using:

• \( Q = m \times c \times \Delta T \)

Accurate heat transfer calculations are critical for understanding how much energy must be added or removed in various scenarios.

Specific heat capacity is a property of a substance that indicates how much heat energy is required to change the temperature of 1 kg of the substance by 1 Kelvin (or 1 degree Celsius). For ethyl alcohol, the specific heat capacity is \(2.43 \, \text{kJ/kg} \cdot \text{K}\).

This property is essential when you want to change the temperature of a substance without changing its phase, as it tells you how energy efficient the material is in storing heat.

In practical problems, specific heat capacity is used in calculations like:

• \( Q = m \times c \times \Delta T \)

where \(Q\) is the heat added or removed, \(m\) is the mass, \(c\) is the specific heat capacity, and \(\Delta T\) is the temperature change. Knowing the specific heat capacity allows us to understand how much energy is necessary to bring ethyl alcohol down from \(78.0^{\circ}C\) to its freezing point of \(-114^{\circ}C\) without it changing phase.