# Changes of State of Matter

## Physical Science - Middle School

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Changes of State Melting Melting is the process of changing from a solid to a liquid state. When thermal energy is added to a solid, the temperature rises and the particles vibrate faster and faster. The particles reach a point when they move out of their fixed positions and the matter becomes a liquid. The temperature at which the solid becomes a liquid is called the melting point. Different materials have different melting points. Freezing Freezing is the process of changing from a liquid to a solid state. It is the opposite process of melting. When thermal energy is removed or lost from a liquid, the temperature becomes cooler and the particles move more slowly. When the particles reach a point when they are no longer moving and are in fixed positions, the matter becomes a solid. The temperature at which the liquid becomes a solid is called the freezing point, which is actually the same temperature as the melting point. solid energy Vaporization Vaporization is the process of changing from a liquid to a gas. There are two types of vaporization, evaporation and boiling. Evaporation occurs when particles on the surface of a liquid are moving fast enough to escape into the air as gas. Boiling occurs when the particles throughout a liquid are moving fast enough to become gas. Water molecules that are heated will vaporize and form bubbles that rise to the surface. The boiling point is the temperature at which a liquid begins to boil. It‘s different for different materials. The molecular structure of a substance determines how much energy is needed for it to change from a liquid to gas. Air pressure also affects the boiling point. When the air pressure surrounding the liquid is higher, more energy is needed for the particles to break free and change to gas. If the air pressure is lower, then less energy is required, and the liquid will boil at a lower temperature. Condensation Condensation is the process of changing from a gas to a liquid. It is the opposite process of vaporization. An example of condensation is when we see water droplets form on the surface of a cold glass. When the air around the glass is cooled, the particles of water vapor in the air move more slowly. The particles begin clumping due to molecular attraction, and the gas changes to liquid water droplets. The temperature at which a gas becomes a liquid is called its condensation point, and it is the same temperature as its boiling point. dry ice (CO 2) carbon dioxide gas warm air fog Sublimation Sublimation is a process that occurs when a material changes from a solid directly into a gas. An example is dry ice, which is extremely cold and is composed of carbon dioxide. When dry ice is removed from a freezer, it acquires thermal energy from the warm air surrounding it, and the solid changes directly to a gas. The cold gas causes water vapor in the air to condense and form fog. © Copyright NewPath Learning. All Rights Reserved. 94-4832 Visit www.newpathlearning.com for Online Learning Resources. material melting point (ºC) iron aluminum tin water 1,538 660 232 0 gas liquid boiling point 100ºC evaporation boiling water molecules gas water molecules liquid water droplets water droplets
Label each of the processes that occur when water changes state. Write down the correct corresponding temperatures that indicate when these changes occur. liquid gas _____ºC _____ºC solid Pause and Review Label each of the processes that occur when water changes state. Write down the correct corresponding temperatures that indicate when these changes occur. Define boiling point, melting point and freezing point. What is the relationship between them? ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ © Copyright NewPath Learning. All Rights Reserved. 94-4832 Visit www.newpathlearning.com for Online Learning Resources. Changes of State