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Changes in states of matter

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There are other kinds of physical changes that occur with water and other substances. When water boils, it turns into a gas: water vapour, but while evaporation occurs only at the surface of the liquid, boiling causes a liquid to turn into a gas below the surface. The bubbles in this boiling water are made up of water vapour. When a liquid boils, the molecules that make up the liquid are put apart to become a gas. Boiling is different from evaporation in another way. While evaporation occurs at different temperatures, each kind of liquid boils at specific temperature called its boiling point. For water the boiling point at sea level is around one hundred degrees Celsius (100ºC) or two hundred twelve degrees Fahrenheit (212ºF). Matter can change from one phase to another in still other ways. As we saw earlier, a solid can change into a liquid when it’s heated. The temperature at which this change happens is called the solid melting point. The melting points of different kinds of rocks are very high, an average about two hundred degrees Celsius (200ºC). The melting point of ice is much lower. At sea level, ice melts at just about zero degrees Celsius (0ºC) or thirty two degrees Fahrenheit (32ºF). Zero degrees Celsius (0ºC) is also the freezing point of water, because at sea level, when the temperature goes below this level, water will turn into solid ice. Most liquids take up less space when they freeze because their molecules are bound more tightly together when they turn into solids, but water is an exception. When water freezes the ice that forms has more volume. Here, for example, one hundred and fifty millilitres (150ml) of water turn into about one hundred and sixty millilitres of ice (160ml). The reason ice has greater volume is that when water freezes its molecules lock together to form rigid but hollow rings. These hollow rings take up more space space than the water molecules did when they were a liquid. There are other unusual exemptions to how matter changes from one phase to another. Dry ice, for instance, is the solid face of carbon dioxide. It is so cold that it causes water vapour in the air to condense into a fine white mist. When it is exposed to warm air, dry ice doesn’t melt. Rather than changing into a liquid, the solid carbon dioxide changes directly into an invisible gas. When matter changes directly from a solid to a gas or from a gas to a solid such a change is called sublimation.

Video Details

Duration: 3 minutes and 4 seconds
Country: Spain
Language: English
Views: 927
Posted by: ang_ruiz on Oct 26, 2011

The phase or state of matter can change when the temperature changes. Generally, as the temperature rises, matter moves to a more active state. Students can learn about this topic by watching the video.

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