Energy changes

• What is an exothermic reaction?

  Thermal energy is released to surroundings
• What is an endothermic reaction?

  Thermal energy is absorbed from surroundings
• What is activation energy?

  The minimum energy for particles to react
• What are bond energies?

  Energy required to break 1 mole of bond
• What happens during bond breaking?

  Energy is absorbed to break bonds
• What happens during bond making?

  Energy is released when bonds form
• What is a reaction profile?

  A diagram showing energies of reactants/products
• What is a cell in chemistry?

  Two electrodes in an electrolyte generating electricity
• What is a battery?

  Two or more chemical cells connected together
• What is an electrolyte?

  A liquid containing ions that conducts electricity
• What is an example of an exothermic reaction?

  Calcium oxide reacting with water
• What is a fuel cell?

  A chemical cell with continuous supply of chemicals
• What is an example of an endothermic reaction?

  Ammonium nitrate dissolving in water
• What is combustion?

  An exothermic reaction involving burning
• What is neutralization?

  A reaction between an acid and a base
• What is the process for energy change calculation in reactions?

  1. Add bond energies of reactants (energy in)
  2. Add bond energies of products (energy out)
  3. Calculate energy change: energy in - energy out
• What is thermal decomposition?

  A reaction where a compound breaks down with heat
• What is photosynthesis?

  An endothermic process in plants
• What are the types of cells in chemistry?

  • Alkaline cell
  • Rechargeable cell
  • Hydrogen fuel cell
• What are the pros and cons of rechargeable cells?

  Pros:

  • Cheaper to manufacture
  • Can be recharged many times
  • No moving parts, only water produced

  
  

  Cons:

  • May end up in landfills when discharged
  • Costs more to manufacture
  • Hydrogen is flammable
• How do reaction profiles differ for exothermic and endothermic reactions?

  Exothermic:

  • Products lower than reactants
  • More energy released than absorbed

  
  

  Endothermic:

  • Products higher than reactants
  • More energy absorbed than released
• What factors affect the voltage of a cell?

  Reactivity difference of metal electrodes and electrolyte
• How does the difference in reactivity of metal electrodes affect voltage?

  The bigger the difference, the higher the voltage
• How does changing the electrolyte affect voltage?

  It can increase or decrease the voltage