New(9-1) AQA GCSE Chemistry Paper 1: Energy Changes Complete Revision Summary

This page contains the detailed and easy notes for AQA GCSE Chemistry Energy Changes for revision and understanding Energy Changes.

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AQA GCSE Paper 1: Complete Revision Summary

Energy Changes

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4.5 Energy Changes

  • Exothermic Reactions
  • Endothermic Reactions
  • Reaction Profile Diagrams
  • Bond Energy Calculations
  • Fuel Cells

TYPES OF REACTIONS

Law of conservation of energy states that energy is neither created nor destroyed. It just converts from one form to another.
Exothermic Reactions ENDOTHERMIC REACTIONS
Reactions that releases heat to the surroundings. Reactions that takes in heat from the surroundings
The reaction is accompanied by increase in temperature of the surroundings as the heat is released. The reaction is accompanied by decrease in temperature of the surroundings as the heat is absorbed.
The product have the lower energy than the reactants. The products have higher energy than the reactants.
Example: Combustion reaction and Respiration Example: Thermal decomposition and -Photosynthesis
In terms of bond breaking the energy released in making the product is more than energy used up in breaking the reactants. In terms of bond breaking the energy used in breaking the bonds of reactants is more than the energy released in making up of the products.
Used in self heating cans and hand warmers Used in Ice packs made for sports injuries
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REACTION PROFILE DIAGRAM

Exothermic Reaction Endothermic Reaction Defining Exothermic and Endothermic in terms of Bond making and Breaking
  Reactants   Products
  Bonds are always broken in a reaction Bonds are always made in a reaction.
Endothermic Breaking of bonds of the reaction takes in heat > Making of bonds of the products Releases heat.
Exothermic Breaking of bonds of the reaction takes in heat      < Making of bonds of the products releases heat.
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BOND ENERGY CALCULATIONS !!

  1. Display the bonds of the reaction and the products
  2. Add the bond energies of the reactants and the products separately
A2 + B2                2AB A-A + B-B                  2[A-B] 221+ 325                 2 x 425 546                850
  1. Take the difference of the two to calculate the heat energy associated with the reaction
Bond Energy
A-A 221
B-B 325
A-B 425
Energy used in breaking the bonds – 546 KJ/mol Energy released in making the bonds – 850KJ/mol Energy associated in overall reaction – 546- 850 = -304 KJ/mol Is it Exothermic or Endothermic – Exothermic as energy is released in products is greater

Cells and Batteries

  • Cell is a device that converts a chemical energy into an electrical energy.
  • A simple cells contains two metal electrode dipped in an electrolytes.
  • Difference in the reactivity of the two metals greater is the voltage produced.
  • The more reactive metal donates electrons to the less reactive metal.
  • The electrons flow from one side to another constituting current and electricity.

FUEL CELLS

At the Negative Electrode 2H2(g) + 4OH–(aq)              4H2O(l) + 4e– At the Positive Electrode O2 + 2H2O + 4e–                4 OH–(aq) Overall – 2H2(g) + O2 (g)                2H2O(l) ADVANTAGES
  • No harmful gases or waste product is produced
  • Waste product is only water so no problem to the environment or disposing off the waste product.
  • Do not needs recharging
DISADVANTAGES
  • Hydrogen is a flammable Gas
  • Production of hydrogen depends on non renewable resources.
  • Hydrogen being a gas is difficult to store and transport
  • Storing and transport of hydrogen involves énergy which comes from fossils fuel thereby it contribute indirectly to -global warming.
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Key terms

Exothermic Reaction – The reaction which gives out heat to the surroundings. Example: Respiration or Combustion Endothermic Reaction – The reactions which taken in heat from the surrounding. Example: Photosynthesis or Thermal decomposition Reaction Profile – Diagramatic representation showing the relative energies of reactants and products in a reaction. Activation – Minimum energy required to start a reaction. Bond Energy – Heat energy contained in a bond between two atoms. Chemical Cells – A device that converts chemical energy into electrical energy. Fuel Cells – A chemical cells that uses a reaction between hydrogen and oxygen to form water and energy. Batteries – collection of cells. Label the reaction profile and classify it as Exothermic or Endothermic

Draw Energy profile diagram of endothermic reaction

Give two application of exothermic and endothermic reaction

  • Exothermic : Self heating cans and hand warmers
  • Endothermic: Ice packs, self cooling cans

State the advantages and disadvantages of fuel cell.

ADVANTAGES
  • No harmful gases or waste product is produced
  • Waste product is only water so no problem to the environment or disposing off the waste product.
  • Do not needs recharging
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    • Hydrogen is a flammable Gas
    • Production of hydrogen depends on non renewable resources.
    • Hydrogen being a gas is difficult to store and transport
    • Storing and transport of hydrogen involves energy which comes from fossils fuel thereby it contribute indirectly to global warming.
Banner 7 Disclaimer: I have tried my level best to cover the maximum of your specification. But this is not the alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it. References: BBC Bitesize Wikipedia Wikimedia Commons Image Source: Wikipedia Wikimedia Commons Flickr Pixabay

Make sure you have watched the above videos and are familiar with the key definations before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well.

C7-Energy Changes