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. The state or phase of a given set of matter can change depending on pressure and temperature conditions, transitioning to other phases as these conditions change to favor their existence; for example, solid transitions to liquid with an increase in temperature. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point, boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms.
Forms of matter that are not composed of molecules and are organized by different forces can also be considered different states of matter.
Superfluids like Fermionic condensate and the quark—gluon plasma are examples. In a chemical equation, the state of matter of the chemicals may be shown as s for solid, l for liquid, and g for gas. An aqueous solution is denoted aq.
Matter in the plasma state is seldom used if at all in chemical equations, so there is no standard symbol to denote it. In the rare equations that plasma is used in plasma is symbolized as p. Glass is a non-crystalline or amorphous solid material that exhibits a glass transition when heated towards the liquid state.
Glasses can be made of quite different classes of materials: inorganic networks such as window glass, made of silicate plus additives , metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. Thermodynamically, a glass is in a metastable state with respect to its crystalline counterpart.
The conversion rate, however, is practically zero. For example the forces between solid helium particles at degrees C are still very weak. By comparison, the forces between iron vapour particles requires very high temperatures are very strong. If you compare different substances that are at the same temperature, then the average kinetic energy of the particles will be the same i. Attractive forces don't get weaker when a substance moves from the solid to the liquid to the gas state, rather the kinetic energy of the particles increases implying faster motion , allowing them to overcome the attractive forces.
Explore the relationships between ideas about movement of particles in the Concept Development Maps - Chemical Reactions, States of Matter. Aim to adopt teaching strategies that promote dissatisfaction in students with their existing ideas, and promote a scientific conception that is plausible, consistent and useful in a variety of situations.
It is important to ascertain the majority of students' prior views at the commencement of teaching to establish their existing understanding of the particle model of matter. Ask students for their ideas about the size of atoms compared with other small things such as cells, bacteria and viruses.
This can be done by asking them to draw the relative size of these on the same scale a scale where a human cell is the size of a page or poster. Bring out the idea that atoms are so much smaller again. Look for other activities that can help reinforce the idea that particles are very, very small. Show students the conventional drawings of particles in solids, liquids and gases and ask them if and how fast they think they are moving.
For more information see: Conservation of mass. With a little encouragement, a class can usually work out by discussion that the particles in gases must be hitting the bottom of the flask harder than the top and hence that they are affected by gravity.
As particles cannot be directly observed, much of the teaching involves looking for apparent problems or inadequacies with the sorts of static pictures of particles given in earlier years.
Encourage students to identify these and talk through possible explanations. Some prompts:. If needed, raise issues such as these, which will open up discussion, but it is better if the students themselves come up with some. Note that many of the issues are to do with gases — it is their properties that we most need a particulate model to explain. To reinforce the notion of elastic collisions, ask what would happen if collisions between gas particles were not elastic.
What practical consequences would there be for people? This can be introduced by dropping different types of balls such as a soccer ball, a table tennis ball and a bouncy ball from toy shops and explaining that a bouncy ball behaves more like gas particles.
Using activities like POE Predict-Observe-Explain can help students think about and then question their existing ideas. The following activity will help students consider their ideas about the movement of particles. Set up two pairs of flasks each connected by a valve see diagrams below. Both pairs have brown nitrogen dioxide in the left hand side flask. The first pair also has air in the right hand side flask. Particle theory helps to explain properties and behaviour of materials by providing a model which enables us to visualise what is happening on a very small scale inside those materials.
As a model it is useful because it appears to explain many phenomena but as with all models it does have limitations. Why do you think that the same volume of different materials have differing masses E.
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