This can mean changing the shape of a natural object, such as carving wood or stone. Or it can mean changing the substance itself, turning it into something else, for example smelting metal ores to extract pure metal. Gases such as air are the lightest state of matter. They are easy to push through, and may not be visible to human eyes. The particles in a gas are not connected to each other, so they can float around freely.
Solids, such as wood and stone, have a fixed shape that is difficult to change. This is because the particles inside them are linked to each other and fixed in place. Liquids such as water can flow freely, changing their shape. The spaces between gas molecules are very big. Gas molecules have very weak or no bonds at all. A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.
In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small or zero for an ideal gas , and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined.
A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature. At temperatures below its critical temperature, a gas is also called a vapor, and can be liquefied by compression alone without cooling. A vapour can 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 above the critical temperature and critical pressure respectively.
In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density confers solvent properties in some cases, which leads to useful applications. For example, supercritical carbon dioxide is used to extract caffeine in the manufacture of decaffeinated coffee. This gives it the ability to conduct electricity. Like a gas, plasma does not have definite shape or volume.
Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. The plasma state is often misunderstood, but it is actually quite common on Earth, and the majority of people observe it on a regular basis without even realizing it.
Lightning, electric sparks, fluorescent lights, neon lights, plasma televisions, some types of flame and the stars are all examples of illuminated matter in the plasma state.
A gas is usually converted to a plasma in one of two ways, either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. A state of matter is also characterized by phase transitions. A phase transition indicates a change in structure and can be recognized by an abrupt change in properties.
A distinct state of matter can be defined as any set of states distinguished from any other set of states by a phase transition. Water can be said to have several distinct solid states.
Likewise, ferromagnetic states are demarcated by phase transitions and have distinctive properties. When the change of state occurs in stages the intermediate steps are called mesophases. Such phases have been exploited by the introduction of liquid crystal technology. 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. 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 When a solid is converted directly into a gas without going through a liquid phase, the process is known as sublimation. Solids, liquids and gases each have their own characteristic properties. In order to explain how these properties come about, the kinetic-molecular theory has been developed. According to this theory, all matter is made up of extremely small particles atoms, molecules or ions , which are in constant motion:.
The classical states of matter solid, liquid and gas can transition directly into any of the other classical states. Either adding heat to the system or removing heat from the system can achieve this. When a gas is heated to very high temperatures, the gaseous atoms are stripped of their outer electrons.
In the s, two scientists, Satyendra Bose and Albert Einstein, predicted the existence of a state of matter at the extreme low-energy end of the temperature scale.
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