Chapter 2 States of matter and substances

(Chapter 1 is not so important for IGCSE so we can skip that, it can be a little bit long since I added other necessary things to the notes which are required by the syllabus.)

States of Matter
Matter is defined as anything that occupies space and has mass.
There are three states of matter

• Solid
• Liquid
• Gas

Its really important to remember this table, the ones in bold are the key ones to remember and write in the exam to get marks.

Remember liquid and gas are known as fluids.

	Solid	Liquid	Gas
Description	Fixed volume, own shape	Fixed volume, takes shape of container	Any volume, takes shape of container
Arrangement of Particles	In a regular pattern called a lattice	Random	Random
Separation of Particles	Close together, touching	Still close together, just slightly further apart than in the solid pace	Separated, far apart.
Movement of Particles	Vibration about a fixed point	Slow movement in a random way from place to place, sliding other each other	Fast random movement
Attractive forces between particles	Stronger than in the liquid pace	Slightly weaker than the solid pace	No attractive forces between particles

All states of matter respond to a change in temperature.

• An increase in temperature will cause the particles in a solid to vibrate more in their fixed positions and take up more space causing expansion. 
• The reverse is contraction which happens when solid is cooled and therefore less energy in the particles, less vibration therefore less space taken up by the particles.
• When the temperature reaches to melting point then the particle have enough energy to move past each other and change positions and the solid changes into a liquid. This is known as melting.
• The reverse of melting is solidification where liquid is cooled and becomes solid. This happens at freezing point which is the same as melting point. Like in water  water melts or solidifies at 0.C

Melting point is the definite temperature where solid changes to a liquid.

• When a liquid is heated, the particle move faster and take up more space causing expansion. 
• When a liquid is cooled, the particles have less energy and move less faster therefore causing a contraction. 
• When the liquid is heated up to its boiling point, the particle in the liquid have enough energy to break intermolecular forces and so the particles separate and become gas or vapor. This is known as boiling. 
• Vapor is a gas which can be compressed into a liquid without cooling.
• The reverse of boiling is condensation where gas is cooled to become a liquid.

Boiling point is the definite temperature where liquid changes to a gas at a constant temperature. If the surrounding pressure decreases the boiling point also decreases.

 Evaporation though happens at all temperatures.

• For solids like dry ice (solid carbon dioxide) they don't turn into a liquid, they turn directly into a gas when heated, This is known as sublimation. 

Pressure

Only fluids (gases and liquids) are compressible, not solids. Liquids are only slightly compressible while gases can be easily compressed. 

In a sealed container the pressure of gases increases when temperature increases. This is because particles of gas will have more energy and will more faster and therefore will hit the walls of container more frequently and harder leading to an increase in pressure. 

This is a frequently asked question IGCSE, why does this happen, therefore it will be good if you understand the answer properly.

Pure Substances

A pure substance consists of only one substance and boils and melts at definite temperatures. Boiling and melting points can be checked to test the purity of a substance. Water that boils at 100C is pure while water that boils at 110C isn't pure.

Impurities in a substance cause-

• The melting point to decrease
• The boiling point to increase.

Mixtures

Mixtures are a system of two or more substances that can be separated by physical means.

It can be of two types-

• Homogeneous- This means the substances are totally mixed up and are indistinguishable like salt and water. Alcohol and water are miscible meaning they make a solution
• Heterogeneous- This means that the substances remain separate and one substance is spread throughout the other as small particle, droplets or bubbles like sand and water. Water and oil are immiscible and separate into different layers.