Unit 8: Rates of reaction
Simple chemical reactions — HIA International - Grade 8 Revision Notes & Topical Questions
5 min read 11 parts Lesson 4 of 10 2 quizzes
Lesson summary
Simple chemical reactions — HIA INTERNATIONAL notes: Distinguish physical and chemical changes and describe simple reactions of metals with oxygen, water and acid using word equations.Physical properties — features such as colour, state, melting and boiling point, and whether the…
- Chemical properties
- Some reactions split a substance apart
- A word equation
- Burning is a chemical reaction
- Carbon + oxygen → carbon dioxide
- Magnesium + oxygen → magnesium oxide
Section 1 of 11Physical and chemical properties
Physical properties
- Physical properties features such as colour, state, melting and boiling point, and whether the substance is heavy or light.
Iron is a grey, heavy solid with a melting point of 1538 °C.
Chemical properties
- Chemical properties features such as how acidic or alkaline a substance is and how it reacts with oxygen, water, acids or metals.
Iron combines with sulfur when heated and with oxygen to form rust.
Section 2 of 11Physical change and chemical change
| Feature | Physical change | Chemical change |
|---|---|---|
| New substance formed | No | Yes |
| Reversibility | Usually easy to reverse | Usually hard to reverse |
| Examples | Melting, freezing, dissolving, boiling | Burning, rusting, cooking, digestion, decay |
| Atoms | Not rearranged | Rearranged into new substances |
Section 3 of 11Reactants and products
Reactants and products
Chemical reaction
Chemical reaction a change in which atoms are rearranged to make new substances.
Reactants
Reactants the substances that react together.
Products
Products the new substances made in the reaction.
Iron + sulfur → iron sulfide.
- The iron atoms combine and bond with the sulfur atoms.
Some reactions split a substance apart
- Some reactions split a substance apart water → hydrogen + oxygen.
A word equation
- A word equation shows the reactants → the products.
Section 4 of 11Burning
Burning
Burning is a chemical reaction
- Burning is a chemical reaction the substance reacts with oxygen in the air, and the new substances are oxides.
Carbon + oxygen → carbon dioxide
- Carbon + oxygen → carbon dioxide charcoal is carbon and leaves ash behind.
Magnesium + oxygen → magnesium oxide
- Magnesium + oxygen → magnesium oxide a white powder.
Combustion
Combustion reaction with oxygen that releases energy: fuel + oxygen → carbon dioxide + water.
Rusting
- Rusting iron + oxygen + water → hydrated iron(III) oxide.
Section 5 of 11Burning magnesium
1
Wear safety glasses and set up a Bunsen burner on a heat-proof mat.
2
Hold a small piece of magnesium ribbon in tongs at arm's length.
3
Place the ribbon in the flame until it catches fire, then remove it.
4
Do not look directly at the flame because the light is very bright.
5
Observe the white powder, magnesium oxide, left behind.
Section 6 of 11Reactants and product when magnesium burns
| Property | Magnesium | Oxygen | Magnesium oxide |
|---|---|---|---|
| Element or compound | Element | Element | Compound |
| State at room temperature | Solid | Gas | Solid |
| Appearance | Soft, shiny, malleable | Colourless, no smell | White powder |
| Conducts electricity | Yes | No | No |
| Melting point | 651 °C | −214 °C | 2800 °C |
Section 7 of 11Reactions with water and acid
Reactions with water and acid
Potassium and water
- Potassium and water potassium is stored under oil because it reacts violently with water,
- giving off hydrogen that burns; only a teacher demonstration is allowed.
Some metals do not react with water at all.
Metal + acid → salt + hydrogen
- Metal + acid → salt + hydrogen for example magnesium + hydrochloric acid → magnesium chloride + hydrogen.
Bubbles show that a gas is made
- Bubbles show that a gas is made but they do not show which gas.
Acid + metal carbonate → salt + water + carbon dioxide
- Acid + metal carbonate → salt + water + carbon dioxide for example calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide.
Section 8 of 11Testing gases
1Hydrogen
- Hydrogen a lit splint at the mouth of the tube gives a squeaky pop, as hydrogen burns with oxygen to form water.
2Keep a finger over the tube until the last moment
- Keep a finger over the tube until the last moment hydrogen is lighter than air and escapes.
3Carbon dioxide
- Carbon dioxide turns limewater cloudy or milky.
4Oxygen
- Oxygen relights a glowing splint.
Section 9 of 11Conservation of mass
1In a reaction atoms are rearranged, not created or destroyed
- In a reaction atoms are rearranged, not created or destroyed so the total mass of the products equals the total mass of the reactants.
2If a gas escapes from an open container
- If a gas escapes from an open container the measured mass appears to fall.
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Chemical reaction | A change in which new substances are formed. |
| Reactant | A substance that takes part in a reaction. |
| Product | A new substance made in a reaction. |
| Word equation | A way to show reactants and products in words, separated by an arrow. |
| Combustion | Burning in oxygen. |
| Oxide | A compound of an element with oxygen. |
| Physical property | A feature such as colour, state or melting point. |
| Chemical property | How a substance reacts with other substances. |
Section 11 of 11Exam technique
1
Saying atoms are used up in a reaction — atoms are rearranged and the total mass stays the same.
2
Thinking melting is a chemical reaction — it is a physical change because no new substance forms.
3
Saying bubbles prove the gas is hydrogen — the gas must be tested.
4
Confusing reactants with products — reactants are on the left and products are on the right of the word equation.
Marked practiceQuizzes for this lesson
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