Cycle Test 2: Combustion, Y7 Recap & States of Matter
In 2 days · Tue 10 Nov
30-minute test on burning fuels, oxidation, fire safety, pollution and the greenhouse effect, plus a Year 7 chemistry recap and states of matter.
1The test
30 minutes. Multiple choice and short answers. Bring a calculator, pen, pencil, ruler and eraser.
| Topic | Section |
|---|---|
| Year 7 recap: naming compounds, formulas, physical vs chemical change | 2 |
| Combustion, fuels and testing the products | 3 |
| Oxidation and conservation of mass | 4 |
| Fire triangle and fire safety | 5 |
| Pollution, greenhouse effect, global warming | 6 |
| States of matter | 7 |
| Key words | 8 |
2Year 7 recap
Naming compounds
- The metal goes first: sodium + chlorine → sodium chloride.
- Two elements only → ending -ide: magnesium oxide, iron sulfide, copper chloride.
- Three elements, one of them oxygen → ending -ate: copper sulfate, calcium carbonate.
Counting atoms and elements in a formula
The small number counts the atom just before it. No number means 1. Each capital letter starts a new element.
| Formula | Name | Elements | Atoms |
|---|---|---|---|
| H₂O | water | 2 (H, O) | 2 + 1 = 3 |
| CO₂ | carbon dioxide | 2 (C, O) | 1 + 2 = 3 |
| CH₄ | methane | 2 (C, H) | 1 + 4 = 5 |
| CaCO₃ | calcium carbonate | 3 (Ca, C, O) | 1 + 1 + 3 = 5 |
| H₂SO₄ | sulfuric acid | 3 (H, S, O) | 2 + 1 + 4 = 7 |
Physical vs chemical change
- Physical change: no new substance, usually easy to reverse. Melting ice, dissolving sugar.
- Chemical change: a new substance is made, usually hard to reverse. Burning, rusting, cooking an egg.
3Combustion and fuels
Combustion means burning a fuel in oxygen. It gives out energy as heat and light, so it is exothermic.
Reactants go on the LEFT of the arrow (what you start with). Products go on the RIGHT (what is made).
Word equations to know by heart
- Complete combustion: hydrocarbon + oxygen → carbon dioxide + water
- Example: methane + oxygen → carbon dioxide + water
- Hydrogen, a clean fuel: hydrogen + oxygen → water
- Incomplete combustion (not enough oxygen): hydrocarbon + oxygen → carbon monoxide + carbon (soot) + water
A hydrocarbon is a compound made of only hydrogen and carbon. Fossil fuels (coal, oil, natural gas) are hydrocarbons. Petrol and diesel come from crude oil.
Testing the products
| Product | Test | Result if present |
|---|---|---|
| Water | Blue cobalt chloride paper | Turns pink |
| Water | White anhydrous copper sulfate | Turns blue |
| Carbon dioxide | Bubble it through limewater | Limewater turns cloudy |
4Oxidation and conservation of mass
Oxidation is a substance reacting with oxygen. The product is an oxide.
- metal + oxygen → metal oxide (magnesium + oxygen → magnesium oxide)
- Non-metals too: carbon + oxygen → carbon dioxide; hydrogen + oxygen → water
- Combustion is a type of oxidation.
Conservation of mass: atoms are not made or destroyed in a reaction, only rearranged. Bonds break and new bonds form. In a closed system (a sealed container) the total mass before = the total mass after.
Why mass can seem to change in an open container
| What happens | Mass looks like it… | Why |
|---|---|---|
| A gas is a reactant (magnesium burning in air) | goes UP | Oxygen from the air joins the solid. That oxygen was never weighed. |
| A gas is a product (wood burning, fizzing) | goes DOWN | The gas escapes into the air and is not weighed. |
Phlogiston was an old idea that burning released a substance called phlogiston. It was proved wrong: burning metals gain mass because they combine with oxygen.
5Fire triangle and fire safety
A fire needs three things: fuel, heat and oxygen. Take away any one side of the triangle and the fire goes out.
| How the fire is put out | Side removed |
|---|---|
| Water on a wood or paper fire | Heat |
| Fire blanket | Oxygen |
| Foam extinguisher | Oxygen |
| Carbon dioxide (CO₂) extinguisher | Oxygen |
| Turning off the gas supply | Fuel |
| Firebreak (clearing trees in a forest fire) | Fuel |
Never use water on
- An oil or petrol fire. The water turns to steam and spreads the burning oil. Use a fire blanket or foam.
- An electrical fire. Risk of electrocution. Use a CO₂ extinguisher.
Hazard symbols show why a chemical is dangerous. The flame symbol means flammable.
6Pollution, greenhouse effect and global warming
Pollutants from burning fuels
| Pollutant | How it is made | Problem | How to reduce it |
|---|---|---|---|
| Carbon monoxide | Incomplete combustion | Toxic | Catalytic converter turns it into CO₂ |
| Soot (carbon particles) | Incomplete combustion | Breathing problems, global dimming | Filters on diesel vehicles |
| Sulfur dioxide | Sulfur impurities in fuel react with oxygen | Acid rain | Remove sulfur from fuel |
| Nitrogen oxides | Nitrogen + oxygen from the air react in hot engines | Acid rain | Catalytic converter turns them into nitrogen + oxygen |
| Carbon dioxide | Complete combustion of fossil fuels | Global warming | Burn less fossil fuel |
The three greenhouse gases to learn: carbon dioxide, methane, water vapour.
The greenhouse effect, step by step
- Energy from the Sun passes through the atmosphere.
- It warms the Earth's surface.
- The warm Earth gives energy back out towards space.
- Greenhouse gases absorb some of it and send it back to the surface.
- This keeps Earth warm enough for life.
Global warming: more greenhouse gases → more energy trapped → the surface gets hotter. Climate change is the change in weather this causes: heatwaves, melting ice, droughts, forest fires, rising sea levels.
| Gas | What increases it | How to reduce it |
|---|---|---|
| Carbon dioxide | Burning fossil fuels, cutting down forests | Renewable energy, walking/cycling/public transport, planting trees |
| Methane | Cattle farming, rice fields, landfill | Eating less meat, recycling and composting |
A carbon footprint is the total carbon dioxide (and other greenhouse gases) released by someone's activities.
7States of matter
| State | Arrangement | Movement | Draw it as |
|---|---|---|---|
| Solid | Touching, neat rows | Vibrate in fixed positions | Neat grid of circles, all touching |
| Liquid | Touching, jumbled | Slide past each other | Circles mostly touching, messy, at the bottom of the box |
| Gas | Far apart, random | Move fast in all directions | A few circles spread far apart |
Changes of state
| Change | From → to | Energy |
|---|---|---|
| Melting | solid → liquid | particles gain energy |
| Evaporating / boiling | liquid → gas | particles gain energy |
| Condensing | gas → liquid | particles lose energy |
| Freezing | liquid → solid | particles lose energy |
Exam phrase: when heated, particles gain energy and vibrate or move faster. They overcome the forces holding them together, so the state changes. When cooled, particles lose energy, slow down, and the forces pull them closer together.
8Key words
| Word | Meaning |
|---|---|
| Combustion | Burning a fuel in oxygen, giving out heat and light |
| Fuel | A substance that stores energy which can easily be released |
| Hydrocarbon | A compound of hydrogen and carbon atoms only |
| Oxidation | A substance reacting with oxygen |
| Reactant | A starting substance; left of the arrow |
| Product | A new substance made; right of the arrow |
| Complete combustion | Burning with plenty of oxygen → carbon dioxide + water |
| Incomplete combustion | Burning with too little oxygen → carbon monoxide, soot and water |
| Pollutant | A substance that harms the environment or living things |
| Carbon footprint | The total greenhouse gases released by someone's activities |
| Exothermic | Gives out energy, so the surroundings warm up |
| Fossil fuel | Coal, oil or gas, formed from dead organisms over millions of years |
| Acid rain | Rain made acidic by sulfur dioxide and nitrogen oxides |
| Catalytic converter | Part of a car exhaust that turns harmful gases into less harmful ones |
| Greenhouse gas | A gas that absorbs energy from the Earth and sends some back (CO₂, methane, water vapour) |