CHAPTER 8

THE STATES OF MATTER

• There are three states of matter
• Liquid,solid and gas.

LIQUID

• Has a definite mass and its volume does not change.It is hard to compress but it flows easily.
• The shape of the liquid varies and depends on the shape of the container holding it.

SOLID

• It does not flow and it is hard to compress.(By squashing it)
• Has a definite mass, a definite shape and its volume does not change.

GAS

• Has a definite mass but its volume can vary and it takes up the shape of the container holding it.It flows easily and it is easy to compress.

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Points of Change

• Phase changes happen when certain points are reached. Sometimes a liquid wants to become a solid. Scientists use something called a FREEZING point or MELTING point to measure the temperature at which a liquid turns into a solid.
• There are physical effects that can change the melting point. Pressure is one of those effects. When the pressure surrounding a substance increases, the freezing point and other special points also go up. It is easier to keep things solid when they are under greater pressure.

WHEN MATTER CHANGES STATE

• All matter can move from one state to another. It may require extreme temperatures or extreme pressures, but it can be done.
• Sometimes a substance doesn't want to change states. You have to use all of your tricks when that happens. To create a solid, you might have to decrease the temperature by a huge amount and then add pressure.
• The state of matter of a substance can be changed.This kind of change is called physical change.

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• It is a reversible reaction.This means that the reaction can go fowards and also backwards, as well as we shall see.
• A physical change of state can be brought about by heating or by cooling.

THE PARTICLE THEORY

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• The particle theory can be used to explain melting in the following way.
• When a solid is heated, the heat provides the particles with more energy.The energy makes the particles vibrate more strongly and push each other a little further apart.
• If the solid is heated further, the energy makes the particles vibrate so strongly that they slide over each other and become a liquid.

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• During the time from when the solid starts to melt until it has completely turned into a liquid, its temperature does not rise.
• All the heat energy is used to separate the particles so that they can flow over one another.

THE PARTICLE THEORY OF MATTER

• Different substances are made from different particles and the particles have different sizes.
• The particles are so tiny that they cannot be seen easily.The particles are atoms and molecules

DISSOLVING

• When something dissolves in a liquid it forms a solution. The liquid its called solute.
• The particle theory explains how things disolve in the following way.There are small gaps between the particles in a liquid.
• When a substance dissolves in a liquid, its particles spread out and fill the gaps.
• How particles in a solid solute are pulled apart by the particles in a liquid solvent, which then move between them.

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• * Evaporation: Is the process by wich a liquid changes into a gas over a range of temperatures.
• Boiling:When a liquid reaches a certain temperature,it forms a gas inside it.The gas makes bubbles,which rise to the surface and burst into the air.
• Condensation:If a gas is cooled down far enough,it turns into this condensation.It is the reverse of evaporating and boiling.
• Sublimationr: A few substances can change from a solid to gas or from a gas to a solid,without forming a liquid.