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13.2Unit 8: Energy changes and reactions of metals

Endothermic reactions

5 min read 5 parts Lesson 2 of 5 1 quiz

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Lesson summary

13.2 Endothermic reactions — CHECKPOINT (CHEMISTRY) notes: Define endothermic reactions and processes and compare them with exothermic ones.Endothermic reaction = a chemical reaction that takes in thermal energy from the surroundings and stores it in chemical bondsEvidence — the …

  • Observation
  • Sherbet sweets
  • Endothermic process
  • Dissolving
  • Evaporation
  • Chemical ice packs

Section 1 of 5Endothermic reactions

  • Endothermic reaction = a chemical reaction that takes in thermal energy from the surroundings and stores it in chemical bonds
  • Evidence
    • the temperature at the end is lower than at the start

Section 2 of 5Citric acid and sodium hydrogen carbonate

  • Equation
    • sodium hydrogen carbonate + citric acid → sodium citrate + water + carbon dioxide
  • Observation
    • the test tube feels cooler and the mixture fizzes
  • Sherbet sweets
    • the same reaction in the mouth gives a cool, fizzy feeling

Section 3 of 5Endothermic processes

  • Endothermic process
    • a change in which no new substance forms but thermal energy is absorbed
  • Dissolving
    • potassium chloride dissolving in water makes the beaker cold
  • Melting
    • ice absorbs energy, its particles vibrate more and overcome the forces holding them in place
  • Evaporation
    • coming out of a pool, water evaporating from skin makes you feel cold

Section 4 of 5Exothermic or endothermic

ExothermicEndothermic
Thermal energyGiven outTaken in
Temperature of surroundingsRisesFalls
ExamplesBurning, neutralisation, condensing, freezingDissolving ammonium nitrate, melting, boiling

Section 5 of 5Using endothermic changes

  • Ice packs
    • ice melting absorbs heat from the injury; the pack can be reused
  • Chemical ice packs
    • dissolving ammonium nitrate in water absorbs heat
    • They work without a fridge or freezer.
  • Investigation
    • measure temperature before and after, using a polystyrene cup to reduce heat transfer

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