Adding or removing energy from matter causes a physical change as matter moves from one state to another. For example, adding thermal energy heat to liquid water causes it to become steam or vapor a gas. And removing energy from liquid water causes it to become ice a solid. Physical changes can also be caused by motion and pressure.
When heat is applied to a solid, its particles begin to vibrate faster and move farther apart. When the substance reaches a certain combination of temperature and pressure, its melting point , the solid will begin to melt and turn into a liquid.
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When two states of matter, such as solid and liquid, are at the equilibrium temperature and pressure, additional heat added into the system will not cause the overall temperature of the substance to increase until the entire sample reaches the same physical state.
For example, when you put ice into a glass of water and leave it out at room temperature, the ice and water will eventually come to the same temperature. As the ice melts from heat coming from the water, it will remain at zero degrees Celsius until the entire ice cube melts before continuing to warm. When heat is removed from a liquid, its particles slow down and begin to settle in one location within the substance. When the substance reaches a cool enough temperature at a certain pressure, the freezing point, the liquid becomes a solid. Most liquids contract as they freeze. Water, however, expands when it freezes into ice, causing the molecules to push farther apart and decrease the density, which is why ice floats on top of water.
Adding additional substances, such as salt in water, can alter both the melting and freezing points. For example, adding salt to snow will decrease the temperature that water freezes on roads, making it safer for drivers. There is also a point, known as the triple point , where solids, liquids and gases all exist simultaneously. Water, for example, exists in all three states at a temperature of Most liquids contract when they freeze but water expands, making it less dense when it becomes ice.
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This unique characteristic allows ice to float in water, like this massive iceberg in Antarctica. When a solid is converted directly into a gas without going through a liquid phase, the process is known as sublimation.
This may occur either when the temperature of the sample is rapidly increased beyond the boiling point flash vaporization or when a substance is "freeze-dried" by cooling it under vacuum conditions so that the water in the substance undergoes sublimation and is removed from the sample. A few volatile substances will undergo sublimation at room temperature and pressure , such as frozen carbon dioxide, or dry ice.
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Vaporization is the conversion of a liquid to a gas and can occur through either evaporation or boiling. Because the particles of a liquid are in constant motion, they frequently collide with each other. Each collision also causes energy to be transferred, and when enough energy is transferred to particles near the surface they may be knocked completely away from the sample as free gas particles. Liquids cool as they evaporate because the energy transferred to surface molecules, which causes their escape, gets carried away with them.
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Liquid boils when enough heat is added to a liquid to cause vapor bubbles to form below the surface. This boiling point is the temperature and pressure at which a liquid becomes a gas. Condensation occurs when a gas loses energy and comes together to form a liquid. For example, water vapor condenses into liquid water. Deposition occurs when a gas transforms directly into a solid, without going through the liquid phase.
Water vapor becomes ice or frost when the air touching a solid, such as a blade of grass, is cooler than the rest of the air. Intermolecular or interatomic or interionic forces are still important, but the molecules have enough energy to move around, which makes the structure mobile. This means that a liquid is not definite in shape but rather conforms to the shape of its container.
Its volume is usually greater than that of its corresponding solid water is a well-known exception to this rule. The highest temperature at which a particular liquid can exist is called its critical temperature. This process of a liquid changing to a gas is called evaporation. Gas molecules have either very weak bonds or no bonds at all, so they can move freely and quickly.
Because of this, not only will a gas conform to the shape of its container, it will also expand to completely fill the container.
Gas molecules have enough kinetic energy that the effect of intermolecular forces is small or zero, for an ideal gas , and they are spaced very far apart from each other; the typical distance between neighboring molecules is much greater than the size of the molecules themselves. A gas at a temperature below its critical temperature can also be called a vapor. A vapor can be liquefied through compression without cooling. It can also exist in equilibrium with a liquid or solid , in which case the gas pressure equals the vapor pressure of the liquid or solid.
A supercritical fluid SCF is a gas whose temperature and pressure are greater than the critical temperature and critical pressure. In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density lends it the properties of a solvent in some cases.
This can be useful in several applications. For example, supercritical carbon dioxide is used to extract caffeine in the manufacturing of decaffeinated coffee. Boundless vets and curates high-quality, openly licensed content from around the Internet.
States of matter (video) | Khan Academy
This particular resource used the following sources:. Skip to main content. Introduction to Chemistry. Search for:. Key Points Matter can exist in one of three main states: solid, liquid, or gas.
What are states of matter?
Solid matter is composed of tightly packed particles. A solid will retain its shape; the particles are not free to move around. Liquid matter is made of more loosely packed particles.
Related States of Matter
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