This between each particle. Solids retain a fixed volume

This essay shall explain the processes involved in changing states of substances. Most substances on earth come in gas, liquid or solid states. Changing between these substances requires energy. Heating or cooling substances is one of the ways, for example water turns into ice once frozen and steam once it is heated.

The kinetic molecular theory of matter is a concept that basically states that atoms and molecules possess kinetic energy that we perceive as temperature. Atoms and molecules are constantly in motion, and we measure the energy of these movements as the temperature of that substance. This means if there is an increase in temperature, the atoms and molecules will gain more energy and move even faster.

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All matter is made up of atoms and these atoms can join up to create molecules. These atoms are in constant motion and when there is a collision between them an exchange of energy between particles occurs however particles in gases do not exert large forces on each other due the wide spaces between each separate particle unless they are in a collision with each other. Molecular motion is greatest in gases, less in liquids, and least in solids due to the distance between each particle. Solids retain a fixed volume and shape as the particles are tightly packed, usually in a regular pattern. Liquids assume the shape of the container in which it occupies but maintains their volume with the particles close together with no regular arrangement. Gases assume the shape and volume of its container and will expand to fill a container of any size.

Water is one of the substances that provide an easy to understanding of the way substances can change between the three states: gas, liquid and water. It moves throughout the environment in a process known as the water cycle.


Heat melts a solid and turns it into a liquid. Cooling freezes a liquid into a solid.

Different solids melt at different temperatures depending on the atoms that make it up some have low or high melting points.


Most solids melt into liquid when they are heated. A liquid evaporates into a gas when it is heated. When a substance is cooled it’s the process of removing heat. Cooling changes a gas into a liquid, and a liquid into a solid. A gas condenses into a liquid when it is cooled. A liquid freezes into a solid when it is cooled.

The closeness, arrangement and motion of the particles in a substance change when it changes state.

The changes in the molecule that are occur when heated are-


·       The movement of its particles increases

·       The bonds between the particles break when a substance melts or evaporates.


When a substance is cooled its internal energy decreases due to the absence of heat. The movement of its particles also decreases.

The bonds between particles form when a substance condenses or freezes.

Particles in substances stay the same during the changes between the states. The chemical nature of the substance also stays the same along with the total mass for example if you boil 10g of water you’ll be left with 10g of steam or 10g of ice if you freeze it. You can measure the change of state by measuring the temperature of a substance.

When you cool a gas substance the changes that occur are either condensation, which is the process of going from a gas to a liquid or freezing, going from a liquid to a solid. The gas particles have a high amount of energy, but as they’re cooled, that energy is reduced. The attractive forces now have a chance to draw the particles closer together, forming a liquid. This process is called condensation. The particles are now in clumps, but as more energy is removed by cooling, the particles start to align themselves, and a solid is formed. This is known as freezing. 





Boiling is also another process, which is when a liquid changes to a gas as the temperature of the water rises and the particles move faster and faster as they absorb the heat and they begin to break. The attractive forces between them break and they start to move freely as steam.

Sublimation is the process where a solid changes to a liquid directly without going through the process of changing from a solid to a liquid to a gas. A common example of this is dry ice.