chemical change. physical changes substance looks different, but chemically still the same. eg....
TRANSCRIPT
Substance looks diff erent, but chemically still the same.
Eg. Melting, breaking.Most physical changes are reversible.
PHYSICAL CHANGES
New substances are formed. Identified by:
Colour change Light or heat produced Precipitate formed
CHEMICAL CHANGE
To save time, we can describe a chemical reaction using equations.
Hydrochloric acid reacts with magnesium metal to produce hydrogen gas and magnesium chloride.
hydrochloric acid + magnesium hydrogen gas + magnesium chloride
WORD EQUATIONS
When writing chemical equations we start with the reactants and end with products.
hydrochloric acid + magnesium hydrogen gas + magnesium chloride
What are the reactants and products in the above word equation?
CHEMICAL EQUATIONS
When a chemical reaction occurs, the particles of the substance rearrange themselves.
Another way to say this is that they change their chemical bonds.
The previous reaction is called ‘respiration’ and is happening in the cells of your body right now.
CHEMICAL REACTIONS
Chemists use chemical reactions to create new substances, for example: Materials such as fabrics, plastics and rubber. Medicines Food products
Or extract particular substances from others for example: Petrol from crude oil Metals from mineral ore
THE WORK OF CHEMISTS