Matter and Energy · 3 min read
Physical Changes in Matter
What Is a Physical Change?
A physical change changes the size, shape, or state of matter without making a new substance. The matter is the same kind of matter before and after the change. Many physical changes can be reversed.
Changes of State: Heating and Cooling
Changing state is a common physical change. When ice melts, it changes from solid water to liquid water. The substance is still water. When liquid water freezes, it changes from liquid to solid. When water boils, it changes from liquid to gas (water vapor). When water vapor condenses, it changes from gas to liquid.
Melting occurs when a solid is heated and changes to a liquid. The melting point is the temperature at which a solid becomes a liquid. Ice melts at 0 degrees Celsius (32 degrees Fahrenheit). Freezing occurs when a liquid is cooled and changes to a solid. The freezing point is the same temperature as the melting point.
Evaporation occurs when a liquid changes to a gas. It can happen at any temperature, and it happens faster when the liquid is warmer. Puddles disappear on a sunny day because the water evaporates into the air as water vapor. Boiling is fast evaporation that happens when a liquid is heated to its boiling point. Water boils at 100 degrees Celsius (212 degrees Fahrenheit) at sea level.
Condensation occurs when a gas cools and changes to a liquid. Water droplets form on the outside of a cold glass because water vapor in the air condenses when it touches the cold surface. Clouds form when water vapor in the atmosphere condenses on tiny particles of dust.
| Change | From → To | Heating or cooling? | Everyday example |
|---|---|---|---|
| Melting | Solid → liquid | Heating | An ice cube melts in your hand |
| Freezing | Liquid → solid | Cooling | Water in a tray becomes ice in the freezer |
| Evaporation | Liquid → gas | Heating | Wet clothes dry on a sunny line |
| Condensation | Gas → liquid | Cooling | Drops form on a cold glass of lemonade |
Predict, Observe, and Record
Scientists predict what will happen, observe carefully, and record their results in a data table. A student predicted that an ice cube on a plate in a warm classroom would melt in about 20 minutes and then recorded these observations:
| Time | Observation | State of the water |
|---|---|---|
| 0 minutes | Hard, cube-shaped, cold | Solid |
| 10 minutes | Smaller cube sitting in a small puddle | Solid and liquid |
| 20 minutes | No ice left; only a puddle | Liquid |
| Next morning | Plate is dry | Water evaporated into the air (gas) |
Other Physical Changes
Cutting, tearing, and breaking are physical changes because they change the size and shape of matter but not the type of matter. Cutting paper into smaller pieces does not change the paper into a different substance.
Dissolving is a physical change. When sugar dissolves in water, the sugar breaks into pieces too tiny to see and spreads through the water, but it is still sugar. The sugar can be recovered by letting the water evaporate.
Bending, stretching, and folding are physical changes that alter the shape of matter. Folding a piece of aluminum foil changes its shape but does not change the aluminum into a different substance.
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