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# Change of State

## Explore the energy required to convert a substance between gas, liquid, and solid

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Change of State

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Most substances exist in any of the three common states of matter: the gaseous, liquid, and solid states. How do these three relate to and differ from each other? How do temperature and molecular motion affect the state of a substance?

In order for a substance to undergo a phase change, it must reach certain temperatures. What is a melting point? A boiling point?

In order for molecules to separate from each other, there needs to be more energy added. This energy is the heat of fusion or heat of melting and is absorbed by the particles as potential energy as a solid change to a liquid.

In order for particles to separate to the gaseous form, they must absorb enough potential energy. This amount of potential energy is called the heat of vaporization.

Tip: vapor hangs in the gaseous air. You can also usually see the steam, or vapor, rising from a boiling pot of water.

The following is a heating curve for water:

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[Figure1]

What do the green arrows represent? Why do the temperatures remain constant at those points?

The heat gained or lost during a temperature change can be found using the equation Q = mc∆t. If the heat gained or lost during a phase change of solid to liquid can be found using Q = mHf, with Hf standing for the heat of fusion in J/kg, what is the equation to find the heat gained or lost during a phase change of liquid to gas?