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13.1Unit 8: Energy changes and reactions of metals

Exothermic reactions

5 min read 5 parts Lesson 1 of 5 1 quiz

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Lesson summary

13.1 Exothermic reactions — CHECKPOINT (CHEMISTRY) notes: Define exothermic reactions and give examples, including burning and metal-acid reactions.Burning (combustion) = a chemical reaction in which a substance combines with oxygenBurning needs fuel, oxygen and heat.Fuel — has a…

  • Energy change
  • Same energy
  • Self-heating cans
  • Fuel — has a store of chemical energy: charcoal, wood, coal, natural gas, oil
  • Exothermic reaction = a chemical reaction in which thermal energy is given out
  • Evidence — the temperature of the surroundings rises

Section 1 of 5Burning

  • Burning (combustion) = a chemical reaction in which a substance combines with oxygen
    • Burning needs fuel, oxygen and heat.
  • Fuel
    • has a store of chemical energy: charcoal, wood, coal, natural gas, oil
  • Energy change
    • chemical energy changes to thermal, light and sound energy that dissipates into the surroundings

Section 2 of 5Exothermic reactions

  • Exothermic reaction = a chemical reaction in which thermal energy is given out
  • Evidence
    • the temperature of the surroundings rises
  • Atoms
    • rearrange into new combinations as chemical energy is changed to thermal energy

Section 3 of 5Examples

ReactionEquation
Hydrogen burninghydrogen + oxygen → water
Magnesium burningmagnesium + oxygen → magnesium oxide
Potassium and waterpotassium + water → potassium hydroxide + hydrogen
Magnesium and acidmagnesium + hydrochloric acid → magnesium chloride + hydrogen
  • Oxidation
    • a reaction in which a substance combines with oxygen; the new substance is an oxide

Section 4 of 5Measuring temperature rise

  1. Measure 10 cm3 of dilute hydrochloric acid into a test tube and record its temperature.
  2. Add an identical piece of magnesium ribbon.
  3. When the reaction stops, measure the temperature again.
  4. Temperature rise = final temperature - start temperature.
  • Same energy
    • the same amount of chemical energy is changed to thermal energy when the amounts are the same
  • Heat loss
    • thermal energy dissipates into the environment, so reduce it with insulation

Section 5 of 5Using exothermic reactions

  • Self-heating cans
    • calcium oxide + water → calcium hydroxide, which gives off heat
    • The compartments must be sealed, so the cans are expensive and can be used only once.
  • Safety
    • wear safety glasses when carrying out reactions

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