Energy Changes

• What is activation energy?

  The minimum energy for successful particle collisions
• Are alkaline batteries rechargeable?

  No, they are non-rechargeable
• What happens in non-rechargeable cells when reactants are used up?

  The chemical reactions stop
• What do batteries consist of?

  Two or more cells connected in series
• What do chemical cells contain?

  Chemicals that react to produce electricity
• What is an endothermic reaction?

  A reaction that takes in energy from surroundings
• What happens to the temperature of surroundings in an endothermic reaction?

  The temperature decreases
• In an endothermic reaction, what is true about the energy of product molecules?

  They have more energy than reactants
• What is an exothermic reaction?

  A reaction that transfers energy to surroundings
• What happens to the temperature of surroundings in an exothermic reaction?

  The temperature increases
• In an exothermic reaction, what is true about the energy of product molecules?

  They have less energy than reactants
• What is the role of activation energy in chemical reactions?

  It is the minimum energy needed to react
• How can reaction profiles be used?

  To show energies of reactants, products, and activation energy
• How can you determine if a reaction is exothermic or endothermic from a reaction profile?

  By comparing the energy levels of reactants and products
• What is the overall energy change of a reaction?

  The difference between energy to break and form bonds
• What happens during a chemical reaction regarding energy?

  Energy is supplied to break bonds and released when formed
• How can you calculate overall energy change?

  Sum of energy to break bonds minus energy to form bonds
• What indicates an endothermic reaction in terms of energy?

  Energy taken in to break > energy released when formed
• What indicates an exothermic reaction in terms of energy?

  Energy taken in to break < energy released when formed
• What do cells contain that produces electricity?

  Chemicals that react
• What factors affect the voltage produced by a cell?

  Type of electrode and electrolyte
• How can a simple cell be made?

  By connecting two different metals with an electrolyte
• What happens in non-rechargeable cells when reactants are used up?

  Chemical reactions stop
• What type of batteries are alkaline batteries?

  Non-rechargeable batteries
• Why can rechargeable cells be recharged?

  The chemical reactions are reversed with current
• What is a fuel cell supplied with?

  An external source of fuel and oxygen
• What happens to fuel in a fuel cell?

  It is oxidised electrochemically to produce voltage
• What is the overall reaction in a hydrogen fuel cell?

  Oxidation of hydrogen to produce water
• What are the advantages and disadvantages of hydrogen fuel cells compared to rechargeable cells and batteries?

  Advantages:

  • Constant use as long as fuel is supplied
  • No need for recharging

  
  

  Disadvantages:

  • Hydrogen needs high-pressure storage
  • Harder to transport
  • Non-biodegradable waste
  • Eventually stops working
• What is the equation at the anode of a hydrogen fuel cell?

  $H_2(g) \rightarrow 2e^- +$$2H^+$$(aq)$
• What is the equation at the cathode of a hydrogen fuel cell?

  $4H^+$$(aq) +$$O_2(g) +$$4e^- \rightarrow 2H_2O(g)$