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Unit 8: Energy changes and reactions of metals

GRADE 7 – Unit 8: Energy changes and reactions of metals — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 1 of 12 1 quiz

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Lesson summary

GRADE 7 - Unit 8: Energy changes and reactions of metals — HIA INTERNATIONAL notes: Classify reactions as exothermic or endothermic and describe the reactions of metals with oxygen, water and acids.Exothermic reaction = thermal energy is given out and the temperature rises.Burnin…

  • Endothermic reaction
  • Endothermic processes
  • Sodium, potassium and calcium
  • Conditions
  • Protection
  • Order of vigour

Section 1 of 9Exothermic reactions

Exothermic reaction
Exothermic reaction thermal energy is given out and the temperature rises.
Burning
  • Burning a fuel reacts with oxygen and chemical energy changes to thermal, light and sound energy.
Examples
  • Examples hydrogen burning, magnesium burning, potassium and water, and magnesium and acid.
Oxidation
  • Oxidation any reaction in which a substance combines with oxygen.

Section 2 of 9Endothermic reactions and processes

1Endothermic reaction
Endothermic reaction thermal energy is taken in and the temperature falls.
2Example
  • Example citric acid with sodium hydrogen carbonate.
3Endothermic processes
  • Endothermic processes dissolving potassium chloride and ice melting, which form no new substance.
4Uses
  • Uses self-heating cans (exothermic) and ice packs (endothermic).

Section 3 of 9Metals and oxygen

1Equation
  • Equation metal + oxygen gives metal oxide.
2Magnesium
  • Magnesium burns brightly to make magnesium oxide.
3Sodium, potassium and calcium
  • Sodium, potassium and calcium react in air and are stored under oil.
4Gold
  • Gold inert.

Section 4 of 9Rusting

Equation
  • Equation iron + oxygen gives iron oxide (rust).
Conditions
  • Conditions water and oxygen are both needed.
Protection
  • Protection painting, oiling and galvanising.

Section 5 of 9Metals and water

Equation
  • Equation metal + water gives metal hydroxide + hydrogen.
Order of vigour
  • Order of vigour potassium, then sodium, then calcium, then magnesium.
Steam
  • Steam metals such as magnesium react more rapidly with steam.
Gold
  • Gold does not react.

Section 6 of 9Metals and dilute acids

Equation
  • Equation metal + acid gives salt + hydrogen.
Salt names
  • Salt names chlorides from hydrochloric acid, sulfates from sulfuric acid and nitrates from nitric acid.
Test for hydrogen
  • Test for hydrogen lit splint gives a squeaky pop.
Reactivity order
  • Reactivity order more reactive metals react faster.

Section 7 of 9Planning investigations

Fair test
  • Fair test change one variable, measure one and keep the others the same.
Preliminary work
  • Preliminary work practise the method first.
Safety
  • Safety risk assessment, safety glasses and screens.
Heat loss
  • Heat loss reduce it with insulation.

Section 8 of 9Key terms

TermMeaning
ExothermicGiving out thermal energy.
EndothermicTaking in thermal energy.
OxidationCombining with oxygen.
ReactivityHow readily a metal reacts.
Metal hydroxideA compound made when a metal reacts with water.
SaltA compound formed when a metal reacts with an acid.
RustIron oxide.
InertUnreactive.

Section 9 of 9Exam technique

1
Calling melting ice an endothermic reaction — it is a process.
2
Saying rusting needs only oxygen.
3
Saying potassium is less reactive than magnesium.
4
Saying a reaction that cools down gives out energy.
5
Saying metals and acid give oxides — they give salts and hydrogen.

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