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THE STATES OF MATTER
THE STATES OF MATTER
MATTER: anything that has a mass and takes up space. There are three physical states: solid, liquid and gas. All the substances and materials of which the universe is composed
CHEMISTRY: the study of how matter behaves and of how one kind of substance can be changed into another.
Chemical substances can be found in three different states of matter: solid, gas and liquid, depending on the pressure and temperature of the substance.
when the temperature increase , the volume increases
when the temperature decreases, the volume decreses
Changes in physical state
Large changes in temperature and pressure can cause changes that are more dramatic than expansion or contraction. They can cause a substance to change its physical state.
Melting and freezing (solid - liquid, liquid - solid)
The temperature at which a pure substance turns to a liquid is called the melting point. This happens at a certain temperature for each substance. The process is reversed at lower temperatures, freezing point. The melting and freezing point are always at the same temperature.
Sublimation (solid - gas, gas - solid)
The solid sublimes when it does not melt and turn directly into gas. This happens at a particular temperature.
Evaporation, boiling and condensation (liquid - gas, gas - liquid)
When liquids change to gases, the process is called evaporation.
Larger the surface, the faster the liquid evaporates
Warmer the liquid, the faster it evaporates
When bubbles appear inside the liquid, the process is known as boiling. It takes place at a specific temperature known as boiling point. eg. Water evaporates fairly easily and has a relatively low boiling point, it is a volatile liquid.
VOLATILE: a liquid which evaporates easily and has a relatively low boiling point.
The reverse of evaporation is condensation. It is possible to condense a gas into liquid by increasing the pressure, without cooling.
The boiling point of a liquid can change if the pressure changes.
Pure substances
A pure substance consists of only one substance not containing impurities.
melt and boils at definite, precise and predictable temperatures
the boiling and the melting point can be used to test the purity of a substance or check their identity
Heating and cooling curves
Using a melting point apparatus we can follow the temperature of the sample before and after melting. These results can be used to produce a heating curve. Similar apparatus can be used to produce a cooling curve.
while the solid is melting the temperature will stop rising
it will begin again to rise when the solid has melted
the heating curve stops at the melting point
the curve shows the melting process over a range of temperatures
in the case of a liquid, you notice it when the liquid is boiling
Heat energy is needed to change state.
Types of mixture
pure substances are not handled very often
each mixture must be made of at least two parts
When two substances that can be of different states are mixed, if they create one single state or phase, this mixture is called solution
salted water: salt is the solute and water is the solvent
in some mixtures the two states are separated, for example a suspension or precipitation
Solutions
A substance dissolving into another is often called solution. A solution is made up of miscible substances or solutions together.
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