CHEMISTRY · Stage 8 · Chapter 9: Chemical Reactions 2
Chemistry 9.11 Chapter 9 Review: Chemical Reactions 2
5 min read 5 parts Lesson 11 of 12
Lesson summary
9.11 Chapter 9 Review: Chemical Reactions 2 — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise combustion, energy changes, calorimetry and the reactions of metals with oxygen, water and acids.Combustion — fuel + oxygen → oxide(s).Oxidation of a metal — metal …
- Thermal decomposition
- Metal with water
- Metal with acid
- Precipitation
- Exothermic
- Endothermic
Part 1 of 5Reaction types and their patterns
- Combustionfuel + oxygen → oxide(s).
- Oxidation of a metalmetal + oxygen → metal oxide.
- Thermal decompositioncompound → simpler substances, such as metal carbonate → metal oxide + carbon dioxide.
- Metal with watermetal + water → metal hydroxide + hydrogen.
- Metal with acidmetal + acid → salt + hydrogen, naming the salt from the acid and the metal.
- Precipitationsodium chloride + silver nitrate → silver chloride + sodium nitrate, where silver chloride is the white precipitate.
Part 2 of 5Energy changes and investigation skills
- Exothermic — it raises the temperature of the surroundings.
- Endothermic — it lowers the temperature of the surroundings.
- Calorimetry — energy transferred (J) = mass of water (g) × 4.2 × temperature rise (°C).
- Divide by the mass of fuel or food burned to compare energy per gram.
- Lower than expected — heat loss and incomplete combustion reduce results; a lid and insulation reduce these errors.
- Fair test — it changes only one variable and controls the others.
Part 3 of 5The reactivity series and its uses
- Rankingmetals are ranked by their reactions with oxygen, water and acids.
- Displacementmore reactive metals react more vigorously and displace less reactive ones from solutions of their compounds.
- Hydrogen's positionit decides which metals react with dilute acid.
- Leadit lies just above hydrogen and is relatively unreactive but toxic.
| Test | Result | Conclusion |
|---|---|---|
| Squeaky pop with lit splint | Positive | Hydrogen |
| Limewater turns cloudy | Positive | Carbon dioxide |
| Temperature rises | Positive | Exothermic |
Part 4 of 5Planning and evaluating
- Plan — list the apparatus, how the independent variable is changed, how the dependent variable is measured and which variables are controlled.
- Repeat measurements, calculate a mean and record results in a table with headings and units.
- Scatter — a graph with scattered points suggests random error.
- Consistently low — points consistently below expectation suggest a systematic error such as heat loss.
- Improvements — use a lid, use a gas syringe instead of an upturned measuring cylinder, or measure at more temperatures.
Part 5 of 5Calculation skills
- Temperature changefinal value minus start value.
- Meanadd the repeat values, ignoring any anomalous result, and divide by the number used.
- Fuelsdivide energy by the mass burned to compare.
- Reactivityrefer to the series, writing the metals in order and using "more reactive" to explain a displacement.
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