Chemical and Physical Properties of Substances
Chemical property
A chemical property may only be observed by changing the chemical identity of a substance. Examples include combustion/explosion or rust
Physical property
A physical property is an aspect of matter that can be observed or measured without changing it. Examples of physical properties include colour, molecular weight and volume
Chemical and physical changes
Difference between compounds and mixtures
Compounds are formed when atoms from different elements join together. Compounds can be produced when two different elements react together but mixing two elements together usually is not enough to cause a chemical reaction.
Mixtures occur when two or more substances come together without reacting. These substances may be elements or compounds.
A useful example to think of is cooking on a barbecue using burning charcoal - the charcoal won't burst into flames on its own.
carbon + oxygen → NO REACTION
For the carbon in charcoal to react with oxygen in the air, an energy source is needed to start the reaction off. In this case, a firelighter must be added:
carbon + oxygen → carbon dioxide
By adding an energy source, the elements carbon and oxygen react to make the compound carbon dioxide
Mixtures occur when two or more substances come together without reacting. These substances may be elements or compounds.
A useful example to think of is cooking on a barbecue using burning charcoal - the charcoal won't burst into flames on its own.
carbon + oxygen → NO REACTION
For the carbon in charcoal to react with oxygen in the air, an energy source is needed to start the reaction off. In this case, a firelighter must be added:
carbon + oxygen → carbon dioxide
By adding an energy source, the elements carbon and oxygen react to make the compound carbon dioxide
Naming new substances
Compounds contain two or more atoms of different elements joined together. The name of a compound tells us the elements present. The suffix, i.e. the ending, of the name tells us if oxygen is part of the compound.
Compound name Elements
Hydrogen sulphide H, S (no oxygen/no metals)
Hydrogen sulphite H, S, O (less oxygen)
Hydrogen sulphate H, S, O (more oxygen)
Compounds contain two or more atoms of different elements joined together. The name of a compound tells us the elements present. The suffix, i.e. the ending, of the name tells us if oxygen is part of the compound.
Compound name Elements
Hydrogen sulphide H, S (no oxygen/no metals)
Hydrogen sulphite H, S, O (less oxygen)
Hydrogen sulphate H, S, O (more oxygen)
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