Phase change of substance can be obtained by heating or cooling. When we heat the substance the temperature will rise until melting point or boil temperature. For example, when we heat ice at below 0oC (let’s say -5oC), it will not melt immediately, but temperature will rise until melting point temperature (0oC) first. Then, ice will melt while the temperature stays at 0oC. After all of water melt, then temperature will rise again until boiled temperature (100 oC). Water temperature will stays at 100 oC, when water is boiled. Then water phase will change to vapor. After all become vapor the temperature will increase again.
For simplifying these phenomena:
- Rising temperature until melting point temperature. The phase is solid
- Phase change from solid to liquid. This phenomenon doesn’t change temperature
- Rising temperature from melting point temperature to boiling point temperature. The phase is liquid
- Phase change from liquid to gas. This phenomenon doesn’t change temperature.
- Rising temperature of gas.
The explanation above is heating process. Cooling process is similar but the opposite.
For calculate heat needed to removed, the general formula are:
- Every Rising temperature: Q = m.c.∆T
- Where Q: heat, m: specific heat of the substance, ∆T: temperature differences
- Change phase from solid to liquid: Q=m.L
- Where L: heat fusion of the substance
- Change phase from liquid to gas: Q = m.U
- Where U: heat of vaporization
These conditions are approach, in actual we may find that water will evaporate although the temperature is not at boiling temperature. Also the other phenomena such as melting.
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