Knowt
Chemical Changes
Physical Change | Chemical Change |
|---|---|
No new substances formed | New substances formed |
Atoms not rearranged | Atoms rearranged |
Reversible using separation techniques | Irreversible |
Heat energy taken in or given out | Heat energy taken in or given out |
Different Types of Chemical Changes interactions
Mixing | Neutralisation | ||||
|---|---|---|---|---|---|
Heat | Thermal Decomposition | ||||
Oxygen | Oxidation | Combustion | Cellular Respiration | Rusting | Browning of Apples |
Light | Photosynthesis | X-Ray | |||
Electricity | Electrolysis | Electroplating |
Neutralisation
Process when an acid reacts with and alkali
Salt and Water is formed
Eg. Hydrochloric acid(acid) reacts with sodium hydroxide(alkali) to form sodium chloride and water
Thermal Decomposition
Process where a substance is broken down into two or more simpler substances when heated
Eg. Copper(II) carbonate is heated to form copper(II) oxide and carbon dioxide
Oxidation
Process where a substance reacts with oxygen
Browning
Exposed surface of apples turn brown due to reaction with oxygen in the air
Combustion
Process where a substance reacts with oxygen in the presence of heat, releasing a lot of it in the process
One or more new substances produced
Eg. Charcoal(carbon) in a barbecue pit burns in oxygen to form carbon dioxide
Eg. Combustion of methane gas(natural) to generate electricity in power plants which forms carbon dioxide and water- If combustion is incomplete, produces carbon monoxide, carbon dioxide and water
Cellular Respiration
Process where living cells of plants and animals take in oxygen to release the energy stored in glucose
To provide cells with energy to grow and reproduce
Carbon dioxide and Water are produced
Rusting
Process where iron reacts with oxygen in the presence of water vapour
Photosynthesis
Process where green plants make food in the presence of light
Electrolysis
Chemical decomposition of substances with the passage of an electric current
Electroplating
Process where a substance is coated with a metal with the passage of an electric current
Acids and Alkalis
Acids- substance that dissolves in water and dissociates (break up) to give hydrogen ions (h+) which is responsible for the properties of an acid
Alkali- substance that dissolves in water and dissociates (break up) to give hydroxide ions (OH-) which is responsible for the properties of an alkali
Acid | Alkali |
|---|---|
pH value less than 7 | pH value of more than 7 |
tastes sour | tastes bitter and feels slippery |
turns blue litmus paper red | turns red litmus paper blue |
no effect on red litmus paper | no effect on blue litmus paper |
turns universal indicator solution to (orange) or red (red) | turns universal indicator solution to blue (weak) or purple (strong) |
corrosive if concentrated | corrosive if concentrated |
conducts electricity when dissolved in water due to free moving hydrogen ions | conducts electricity when dissolved in water due to free moving hydroxide ions |
pH scale
0-3 | Strong acid |
|---|---|
4-6 | weak acid |
7 | neutral |
8-10 | weak alkali |
11-14 | strong alkali |
C H O M
Acids react with… | Carbonates | Hydroxides and Oxides | Metals |
|---|---|---|---|
Forms? | Salt, Carbon dioxide gas and water | Salt and Water | Salt and Hydrogen Gas |
Example | Calcium Carbonate reacts with hydrochloric acid to form calcium chloride, water and carbon dioxide | Sodium Hydroxide and nitric acid reacts to form sodium nitrate and water | |
Example | Potassium Carbonate reacts with sulfuric acid to form potassium sulfate, water and carbon dioxide | Sodium Oxide and nitric acid reacts to form sodium nitrate and water | |
How to test for it | Bubble the gas through limewater (calcium hydroxide) in which a white precipitate will form | Insert a lighted splint into the test tube of hydrogen gas in which the lighted splint will extinguish with a ‘pop’ sound |
