Energy changes

  • Created by: holly6901
  • Created on: 04-04-19 16:41

Energy transfer/conservation

Endothermic reactions

Energy from the surroundings is transferred to the reacting chemicals, causing the temperature of the surroundings to decrease. Examples include:

  • Thermal decomposition.
  • The reaction between citric acid and sodium hydrogen carbonate (sodium bicarbonate).

Exothermic reactions 

Energy from the reacting chemicals is transferred to the surroundings, which often increase in temperature as a result. Examples include:

  • Combustion.
  • Neutralisation.
  • Oxidation.
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Exothermic reactions

In exothermic reactions, energy from the reacting chemicals is transferred to the surroundings. This often leads to an increase in temperature. Examples include:

  • Oxidation
  • Hand warmers
  • Disposable hand warmers use the energy released by iron oxidation.
  • Reusable hand warmers source their energy from the crystallisation of salt solutions. Boiling the pack re-dissolves the crystals, so that it's ready to be activated once more.
  • Combustion
  • Neutralisation
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Endothermic reactions

In endothermic reactions, energy from the surroundings is transferred to the reacting chemicals. This decreases the temperature of the surroundings. Examples include:

  • Sports injury packs
  • When squeezed forcefully, ammonium nitrate and water mix in the pack, resulting in instant cooling.
  • The speed of this reaction makes these packs ideal for scenarios when ice is not immediately available.
  • Thermal decomposition
  • Citric acid and baking soda
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Requirements for a reaction

There are 2 main requirements for a successful reaction to take place:

  • Collisions
  • Reacting particles must collide.
  • Activation energy
  • Collisions must take place with sufficient energy (the activation energy).
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Reaction profiles

Reaction profiles show the progress of reaction on the x axis and energy level on the y axis. They contain the following information:

  • The relative energies of reactants and products.
  • The activation energy of a reaction.
  • The overall energy change of a reaction.
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Catalysts

Catalysts can increase reaction rates by lowering the activation energy, which increases the likelihood of successful collisions.

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