Exothermic and Endothermic Reactions

• What happens to energy during chemical reactions?

  Energy changes occur; it moves around.
• What indicates that energy is taken in during a reaction?

  The products store more energy than reactants.
• What happens if the products store less energy than the reactants?

  Excess energy is transferred to surroundings.
• What does the conservation of energy state in reactions?

  Energy cannot be created or destroyed.
• What is an exothermic reaction?

  It transfers energy to the surroundings.
• What type of reaction is neutralization?

  Neutralization reactions are exothermic.
• What happens when sodium is added to water?

  It releases energy, indicating exothermic reaction.
• What are some everyday uses of exothermic reactions?

  • Hand warmers using iron oxidation
  • Self-heating cans of beverages
• What is an endothermic reaction?

  It takes in energy from the surroundings.
• What indicates an endothermic reaction?

  A fall in temperature is observed.
• What happens during thermal decomposition of calcium carbonate?

  It decomposes into calcium oxide and carbon dioxide.
• How are endothermic reactions used in sports injury packs?

  • Chemical reaction cools the pack instantly
  • No need for freezer
• What is the energy change when ice melts?

  Melting ice is an endothermic process.
• What does 'exo' mean in exothermic reactions?

  'Exo' means 'out'.
• What does 'endo' mean in endothermic reactions?

  'Endo' means 'in'.
• How can you measure energy released in a reaction?

  By measuring temperature changes in a solution.
• What is a major problem when measuring energy changes?

  Energy lost to the surroundings is significant.
• How can you reduce energy loss during measurements?

  Use insulation and a lid on the cup.
• What types of reactions can be measured using this method?

  Neutralisation and reactions with acids.
• How can you test the effect of acid concentration on energy released?

  1. Prepare different concentrations of acid.
  2. Mix with sodium hydroxide in a polystyrene cup.
  3. Measure temperature changes over time.
• What do reaction profiles show?

  • Relative energies of reactants and products
  • Energy changes during the reaction
• What does a reaction profile for an exothermic reaction indicate?

  Products are at lower energy than reactants.
• What does the initial rise in energy on a reaction profile represent?

  It represents the activation energy needed.
• What is activation energy?

  Minimum energy needed for reactants to collide.
• What does a reaction profile for an endothermic reaction indicate?

  Products are at higher energy than reactants.
• What does the height difference in a reaction profile represent?

  Overall energy change during the reaction.
• What is the equation for the combustion of methane?

  CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
• What should you include in a reaction profile for combustion of methane?

  • Initial energy of reactants
  • Final energy of products
  • Activation energy required