chemistry topic 5 energy changes

• What is conserved during chemical reactions?

  Energy
• What does it mean when a reaction transfers energy to the surroundings?

  Product molecules have less energy than reactants
• What is an exothermic reaction?

  Transfers energy to the surroundings
• What happens to the temperature of surroundings during an exothermic reaction?

  The temperature increases
• What is an endothermic reaction?

  Takes in energy from the surroundings
• What happens to the temperature of surroundings during an endothermic reaction?

  The temperature decreases
• What are some applications of endothermic reactions?

  Sports injury packs
• What is the term for energy released to the surroundings during a reaction?

  Exothermic
• What is required for chemical reactions to occur?

  Reacting particles must collide with sufficient energy
• What do you call the substances that undergo a chemical reaction?

  Reactants
• What is activation energy?

  Minimum energy required for particles to react
• What is the term for the energy required to start a reaction?

  Activation energy
• How does activation energy relate to chemical reactions?

  It is the minimum energy needed to initiate a reaction
• What is the term for the substances formed as a result of a chemical reaction?

  Products
• How can you determine if a reaction is exothermic or endothermic?

  By comparing the energy of reactants and products
• What happens to the energy of products in an exothermic reaction?

  Products have less energy than reactants
• What happens to the energy of products in an endothermic reaction?

  Products have more energy than reactants
• 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 is the energy change during a chemical reaction?

  • Energy must be supplied to break bonds in reactants
  • Energy is released when bonds in products are formed
• What is a battery composed of?

  Two or more cells connected in series
• What happens in non-rechargeable cells and batteries?

  Chemical reactions stop when reactants are used up
• What type of batteries are alkaline batteries?

  Non-rechargeable
• How can you calculate the overall energy change of a reaction?

  Sum of energy to break bonds - sum to form bonds
• Why can rechargeable cells and batteries be recharged?

  The chemical reactions are reversed with external current
• What do fuel cells require as inputs?

  Fuel and oxygen or air
• What indicates an endothermic reaction in terms of energy?

  Energy taken in to break > energy released
• What is the overall reaction in a hydrogen fuel cell?

  Oxidation of hydrogen to produce water
• What indicates an exothermic reaction in terms of energy?

  Energy taken in to break < energy released
• How do hydrogen fuel cells compare to rechargeable cells and batteries?

  • Hydrogen fuel cells can be used constantly
  • Rechargeable cells need to be recharged
  • Fuel cells require continuous fuel supply
  • Rechargeable cells can reverse reactions
• What is a disadvantage of hydrogen as a fuel for fuel cells?

  It needs to be stored under high pressure
• What are the key differences between exothermic and endothermic reactions?

  Exothermic:

  • Heat released to surroundings
  • Products have less energy than reactants

  
  

  Endothermic:

  • Heat taken in from surroundings
  • Products have more energy than reactants
• What is produced when hydrogen is burnt in a fuel cell?

  Water
• What is the equation for the reaction at the anode in a hydrogen fuel cell?

  H₂(g) -> 2e + 2H(aq)
• What is the equation for the reaction at the cathode in a hydrogen fuel cell?

  4H(aq) + O₂(g) + 4e -> 2H₂O(g)
• What are the advantages and disadvantages of hydrogen fuel cells?

  Advantages:

  • Constant energy supply
  • Reversible reactions

  
  

  Disadvantages:

  • Requires high-pressure storage
  • Non-biodegradable waste
  • Difficult to transport