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Simple Explanation:
To review on the states of matter and phase diagrams, check out this tutorial.
Phase Change Diagram Example:
These diagrams represent the changes in states of matter in regards to potential energy (heat energy) and temperature (average kinetic energy).
Analysis of Phase Change Diagrams:
The sloped parts of the diagram represent the increasing temperature during a specific phase.
The plateau parts of the diagram represent the transition of phases for the substance. The slope should be near zero during this process, because most of the energy would be used to overcome the attraction forces between particles instead of raising the temperature.
This is an equilibrium process.
The process of vaporization generally takes longer than the process of melting if the rate of increase for potential energy stays constant, because you would have to overcome more attraction forces.
Progressing rightwards of the diagram is endothermic, while progressing leftwards is exothermic.
Energy Transfer in Phase Changes
Here are the formulas to calculate energy transfer in phase changes:
Specific Heat Capacity Formula:
q = mcΔT
q: Heat Energy (J)
m: Mass of Substance (g)
c: Specific Heat of Substance (J/g°C)
ΔT: Change in Temperature, Tf - Ti (°C)
This formula ties the relationships of energy, mass, specific heat capacity, and temperature together.
Heat of Fusion Formula:
q = mHf
q: Heat Energy (J)
m: Mass/Moles of Substance (g or mol)
Hf: Heat of Fusion (J/g if using mass, KJ/mol if using moles)
This formula describes how much energy is needed to melt a substance. Multiply q by -1 to find the amount of energy release needed for its exothermic counterpart (freezing). The value of Hf will be given.
Heat of Vaporization Formula:
q = mHv
q: Heat Energy (J)
m: Mass/Moles of Substance (g or mol)
Hv: Heat of Vaporization (J/g if using mass, KJ/mol if using moles)
This formula describes how much energy is needed to vaporize a substance. Multiply q by -1 to find the amount of energy release needed for its exothermic counterpart (condensing). The value of Hv will be given.
Formulas of Phase Change Visualization
This visualization shows when a formula should be used.
Solving for Overall Energy Change:
You can add the q values up to find the overall energy change.
qtotal = q₁ + q₂ + q₃ + q₄ + q₅
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