The Enthalpy Change of Phase Transitions
When a substance undergoes a phase transition, it changes from one physical state to another. This can be seen when a solid changes to a liquid or when a liquid changes to a gas. As the molecules of the substance become less ordered and more chaotic during the transition, their enthalpy change must also be taken into account during the transition. The enthalpy change of a phase transition is a measure of how much energy is released or absorbed during the process.
Since the enthalpy change of a phase transition is an important thermodynamic value, it can be studied using a variety of tools. The main tools used to study the enthalpy change of a phase transition are: specific heat capacity, calorimetry, and isothermal transformation diagrams.
The specific heat capacity of a substance is the amount of energy needed to raise the temperature of a unit mass of the substance by one degree. Through calorimetry, which measures the amount of heat evolved or absorbed by a substance during a reaction, it is possible to calculate the enthalpy change of a phase transition for a given reaction. Isothermal transformation diagrams also allow for the calculation of the enthalpy change of a phase transition by measuring the temperatures at which the transition from one physical state to another occurs.
Isothermal transformation diagrams are particularly useful for illustrating phase transitions because they can graphically depict phase transitions for any particular substance. The diagrams plot the enthalpy change of a phase transition on the y-axis and the temperature on the x-axis. For each temperature, the enthalpy values are graphed, and these values are known as transformer curves. At each temperature along the curve, the phase corresponding to the enthalpy value is present, while at all other temperatures between the points, the phase remains constant. This is useful as it allows us to determine the exact temperature range in which the phase transition occurs.
The enthalpy change of a phase transition is an important thermodynamic value, and knowledge of it can be used to determine the energy requirements for a particular substance to change between physical states. A number of tools can be used to investigate the enthalpy change of a phase transition and one of those is the isothermal transformation diagram. By using this method, it is possible to gain a better understanding of how temperature affects the physical states of a substance and how much energy is required for the phase transition to occur.
