energy changes

• What is an exothermic reaction?

  An exothermic reaction transfers energy to the surroundings, usually by heating.
• How is an exothermic reaction indicated in terms of temperature?

  It is indicated by a rise in temperature.
• What is an example of an exothermic reaction?

  Burning fuels (combustion) is an example of an exothermic reaction.
• What type of reactions are neutralisation reactions?

  Neutralisation reactions are exothermic reactions.
• What are some everyday uses of exothermic reactions?


  Hand warmers and self-heating cans are everyday uses of exothermic reactions.
• What is an endothermic reaction?

  An endothermic reaction takes in energy from the surroundings.
• How is an endothermic reaction indicated in terms of temperature?


  It is indicated by a fall in temperature.
• What is an example of an endothermic reaction?


  The reaction between citric acid and sodium hydrogencarbonate is an example of an endothermic reaction.
• What are some everyday uses of endothermic reactions?

  Sports injury packs and fridges are everyday uses of endothermic reactions.
• What are the key differences between exothermic and endothermic reactions?


  • Exothermic reactions:
  • Transfer energy to surroundings
  • Indicated by a rise in temperature
  • Examples: combustion, neutralisation, oxidation, respiration
  • Everyday uses: hand warmers, self-heating cans

  
  

  • Endothermic reactions:
  • Take in energy from surroundings
  • Indicated by a fall in temperature
  • Examples: reaction between citric acid and sodium hydrogencarbonate, thermal decomposition, photosynthesis
  • Everyday uses: sports injury packs, fridges
• What type of reaction transfers energy to the surroundings?

  Exothermic reaction
• How is an exothermic reaction indicated?

  By a rise in temperature
• What is an example of an exothermic reaction?

  Burning fuels
• What type of reaction is neutralization?

  Exothermic reaction
• What are two other examples of exothermic reactions?

  Oxidation reactions and respiration
• What are everyday uses of exothermic reactions?

  Hand warmers and self-heating cans
• What does an endothermic reaction do?

  Takes in energy from surroundings
• How is an endothermic reaction indicated?

  By a fall in temperature
• What is an example of an endothermic reaction?

  Citric acid and sodium hydrogencarbonate reaction
• What are everyday uses of endothermic reactions?

  Sports injury packs and fridges
• What is the difference between exothermic and endothermic reactions?

  • Exothermic: Releases energy, temperature rises
  • Endothermic: Absorbs energy, temperature falls
• What is activation energy?

  Energy needed to start a reaction
• What happens to energy during exothermic and endothermic reactions?

  • Exothermic: Energy out, temperature increases
  • Endothermic: Energy in, temperature decreases
• What is bond energy?

  Energy required to break a bond
• What happens to bonds during a chemical reaction?

  All bonds are broken, then new ones formed
• What is the bond energy of C-H?

  413 kJ/mol
• What is the bond energy of O=O?

  495 kJ/mol
• What is the bond energy of C=O?

  799 kJ/mol
• What is the bond energy of O-H?

  467 kJ/mol
• What is the total bond energy for the reactants in the reaction $CH₄ +$$2O₂ → CO₂ +$$2H₂O$?


  $2642 kJ/mol$
• What is the total bond energy for the products in the reaction $CH₄ +$$2O₂ → CO₂ +$$2H₂O$?


  $3466 kJ/mol$
• What does a negative net energy change indicate in a reaction?

  It is an exothermic reaction
• What is the net energy change for the reaction $CH₄ +$$2O₂ → CO₂ +$$2H₂O$?


  $-824 kJ/mol$
• What are the components of a cell in a battery?

  • Two different metals
  • An electrolyte
• What do cells produce when chemicals react?

  A potential difference
• What happens to non-renewable cells after use?


  They cannot be reused
• What is a characteristic of renewable batteries?

  They can perform reverse reactions
• What do hydrogen fuel cells contain?

  Hydrogen and oxygen
• What happens when hydrogen and oxygen recombine in fuel cells?

  It produces a potential difference