PMT

• What is the conservation of energy principle?

  Energy is conserved in chemical reactions
• What does the conservation of energy principle state about energy in the universe?

  The amount of energy remains the same
• What is an exothermic reaction?

  Energy is transferred to the surroundings
• What happens to the temperature of surroundings in an exothermic reaction?

  The temperature of surroundings increases
• What is an endothermic reaction?

  Energy is taken in from the surroundings
• What happens to the temperature of surroundings in an endothermic reaction?

  The temperature of surroundings decreases
• What is activation energy?

  Minimum energy needed for particles to react
• What is a reaction profile?

  A graph showing energies of reactants and products
• What does a reaction profile indicate about activation energy?

  It shows the activation energy of the reaction
• Describe exothermic and endothermic reactions in terms of bond energies.

  • Exothermic: Energy released from forming bonds > energy needed to break bonds
  • Endothermic: Energy needed to break bonds > energy released from forming bonds
• What is the equation to find enthalpy change in terms of bond energies?

  Energy of reaction = bonds broken - bonds made
• What is a cell?

  A cell produces electricity from a chemical reaction
• What is a battery?

  A battery consists of two or more cells
• What determines the voltage obtained from a cell?

  Identities of metals and electrolyte concentration
• What are the advantages and disadvantages of using cells and batteries?

  Advantages:

  • Cheap
  • Some are rechargeable
  • Convenient energy source

  
  

  Disadvantages:

  • Harmful chemicals
• Describe rechargeable and non-rechargeable cells.

  • Rechargeable: Reactions reversed with external current
  • Non-rechargeable: Reactants used up, cannot be recharged
• What is a fuel cell?

  Fuel cells generate electricity from fuel and oxygen
• What is the overall reaction in a hydrogen fuel cell?

  2 H2 + O2 → 2 H2O
• What are the half equations in a hydrogen fuel cell?

  Cathode: 2 H2 → 4 H+ + 4 e−; Anode: O2 + 4 H+ + 4 e− → 2 H2O
• What are the advantages and disadvantages of hydrogen fuel cells?

  Advantages:

  • No pollutants
  • No recharging needed

  
  

  Disadvantages:

  • Flammable
  • Difficult to store H2
  • Fossil fuel production
  • Toxic chemicals
  • Expensive H2 production