C5

Cards (22)

  • What is conserved in chemical reactions?
    Energy is conserved in chemical reactions.
  • What happens to the overall amount of energy in the universe after a chemical reaction?
    The overall amount of energy in the universe remains the same.
  • What type of reaction takes in energy from the surroundings?
    An endothermic reaction takes in energy from the surroundings.
  • How is an endothermic reaction indicated in terms of temperature?
    It is shown by a fall in temperature.
  • What are examples of endothermic reactions?
    • Thermal decompositions
    • Citric acid + sodium hydrogencarbonate
    • Used in some sports injury packs
  • What type of reaction transfers energy to the surroundings?
    An exothermic reaction transfers energy to the surroundings.
  • How is an exothermic reaction indicated in terms of temperature?
    It is shown by a rise in temperature.
  • What are examples of exothermic reactions?
    • Combustion
    • Neutralisation
    • Most oxidation reactions
    • Used in self-heating cans and hand warmers
  • What is activation energy?
    Activation energy is the minimum amount of energy that reactants need to react.
  • What is the difference between bond breaking and bond forming in terms of energy?
    • Bond breaking is endothermic (energy absorbed).
    • Bond forming is exothermic (energy released).
  • In endothermic reactions, what is true about the energy used to break bonds compared to the energy released by forming new bonds?
    The energy used to break bonds is greater than the energy released by forming new bonds.
  • In exothermic reactions, what is true about the energy released by forming bonds compared to the energy used to break existing bonds?
    The energy released by forming bonds is greater than the energy used to break existing bonds.
  • What is a cell in the context of electrochemical cells?
    • A simple cell allows the charge to flow.
    • Reactions between electrolyte and electrodes set up a charge difference.
  • What do electrochemical cells use to produce electricity?
    They use chemical reactions to produce electricity.
  • What is a battery?
    A battery is two or more cells connected in series.
  • What happens to non-rechargeable cells and batteries once one reactant is used up?
    They can't be recharged.
  • What is the characteristic of rechargeable cells and batteries?
    The reaction in the cell is reversible.
  • What is the anode reaction in a hydrogen fuel cell?
    The anode reaction is \( H_2 \rightarrow 2H^+ + 2e^- \).
  • What is the cathode reaction in a hydrogen fuel cell?
    The cathode reaction is \( O_2 + 4H^+ + 4e^- \rightarrow 2H_2O \).
  • What is the overall equation for the reaction in a hydrogen fuel cell?
    The overall equation is \( 2H_2 + O_2 \rightarrow 2H_2O \).
  • What are the advantages of hydrogen fuel cells compared with batteries?
    • Less pollution over cell's lifetime.
    • Don't need recharging/replacing as often.
    • Cheaper to make.
  • What are the disadvantages of hydrogen fuel cells compared with batteries?
    • Storage of H₂ gas takes up more space.
    • H₂ production can emit greenhouse gases.
    • H₂ is explosive - hard to store safely.