CHEMISTRY · Stage 8 · Chapter 9: Chemical Reactions 2
Chemistry Stage 8 Comprehensive Review
5 min read 7 parts Lesson 12 of 12
Lesson summary
Stage 8 Comprehensive Review — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise atoms, mixtures, reactions and energy changes from Stage 8 chemistry.Sub-atomic particles — protons (charge +1) and neutrons (charge 0) are in the nucleus, and electrons (charge -…
- Proton number
- Nucleon number
- Filtration
- Evaporation or crystallisation
- Distillation
- Chromatography
Section 1 of 7Atoms, elements and compounds
- Sub-atomic particles
- protons (charge +1) and neutrons (charge 0) are in the nucleus, and electrons (charge -1) occupy shells outside it.
- Proton number
- the number of protons, which equals the number of electrons in a neutral atom.
- Nucleon number
- protons plus neutrons.
- Element
- it contains only one type of atom.
- Compound
- it contains two or more elements chemically joined in fixed proportions, with different properties from the elements that formed it.
Section 2 of 7Mixtures, solutions and separation
- Mixture
- it is not chemically joined and can be separated by physical methods.
- Filtration
- it separates insoluble solids from liquids.
- Evaporation or crystallisation
- they separate dissolved solids.
- Distillation
- it separates liquids with different boiling points.
- Chromatography
- it separates dissolved colours.
- Pure substance
- it melts at one sharp temperature.
- Solubility
- it is the mass dissolving in 100 g of solvent, and for most solids it rises with temperature.
Section 3 of 7Chemical reactions and energy
- Chemical reaction
- new substances form and the total mass is conserved because atoms are rearranged.
- Types
- combustion, oxidation, thermal decomposition, and reactions of metals with water, acids and oxygen.
- Exothermic
- it releases energy and raises the temperature.
- Endothermic
- it absorbs energy and lowers the temperature.
- Calorimetry
- burning a fuel under water lets us calculate the energy transferred as mass of water × 4.2 × temperature rise.
- Energy lost
- energy not transferred to the water goes to the air, the container or the apparatus, and also as sound and light.
| Idea | Key fact |
|---|---|
| Proton number | Number of protons = number of electrons in an atom |
| Reactivity | Metals above hydrogen react with acids |
| Fair test | Change one, measure one, control the rest |
Section 4 of 7Particle ideas that link the topics
- Solid
- particles vibrate in fixed positions.
- Liquid
- particles move past one another.
- Gas
- particles move freely and far apart.
- Melting and boiling points
- heating raises particle energy until the forces holding them are overcome, so these points identify substances.
- Solutions
- solute particles are surrounded by solvent particles, and heating usually allows more to dissolve.
- Reactions
- atoms are rearranged and the number of atoms of each element stays the same.
Section 5 of 7Periodic table and reactivity
- Order
- the periodic table lists elements in order of atomic number.
- Metals
- they form positive ions by losing outer electrons, and reactivity is linked to how easily they do this.
- This explains the reactivity series and the reactions of metals with oxygen, water and acid.
- Non-metals
- they tend to gain or share electrons.
Section 6 of 7Energy ideas
- Fuels
- they release chemical energy when they burn, which is transferred to thermal energy in the surroundings.
- Conservation
- energy is conserved but spreads out into less useful forms.
Section 7 of 7Handling data
- Graphs
- plot the independent variable on the x-axis and the dependent variable on the y-axis, and draw a line of best fit with a ruler or smooth curve.
- Anomalous results
- identify them and explain why they might occur.
- Fuel comparison
- burning 1 g of each of four fuels gives a larger temperature change for more energy transferred, since the mass is the same.
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