1. Chemistry in our world

2. Acids metal + Acid-> salt + hydrogen
Magnesium + hydrochloric acid -> magnesium chloride + hydrogen
We can test for hydrogen by holding a lighted splint over the test tube and listening for a pop

3. Neutralisation
Acid + alkali (e.g. Calcium carbonate) makes a neutral substance
Calcium carbonate + hydrochloric acid -> calcium chloride + water + carbon dioxide
Limewater turns cloudy when carbon dioxide reacts with it

4. Temperature changes
The reaction between citric acid and sodium hydrogen carbonate feels cold – it takes heat in from the surroundings
We can speed up a chemical reaction by heating it up

5. Atmosphere The early atmosphere on Earth was mostly carbon dioxide
The early atmosphere was produced by volcanic activity
The oceans were made when water vapour condensed
Today, there is 20% oxygen in the atmosphere

6. Fossil fuels Crude oil is a mixture of compounds
Crude oil is found in underground deposits
Some greenhouse gases make the Earth’s temperature rise
Sulfur dioxide makes acid rain, kills plants and damages buildings

7. Water To make water safe to drink we need to sterilise it
We do this to kill the bacteria in it