Exothermic and Endothermic Reactions

• What are the two types of reactions based on energy changes?

  Exothermic and Endothermic reactions
• What happens to energy during chemical reactions?

  Energy is either taken in or released during chemical reactions
• What does it indicate if the products of a reaction store more energy than the reactants?


  Energy has been taken in during the reaction
• What occurs if the products of a reaction store less energy than the reactants?


  The excess energy is transferred to the surroundings
• What is the principle regarding the total amount of energy in a chemical reaction?


  The total amount of energy does not change; it is only moved around
• What is an exothermic reaction?


  An exothermic reaction is one that transfers energy to the surroundings
• How is an exothermic reaction indicated?


  By a rise in temperature
• What is the best example of an exothermic reaction?


  Burning fuels, also known as combustion
• What type of reaction is neutralization?

  Neutralization reactions are exothermic
• What is an example of an exothermic oxidation reaction?


  Adding sodium to water
• What are some everyday uses of exothermic reactions?


  Hand warmers and self-heating cans
• What is an endothermic reaction?


  An endothermic reaction is one that takes in energy from the surroundings
• How is an endothermic reaction indicated?


  By a fall in temperature
• What is a common example of an endothermic reaction?


  The reaction between citric acid and sodium hydrogencarbonate
• What is thermal decomposition?


  It is an endothermic reaction where a compound breaks down into simpler substances when heated
• What is the equation for the thermal decomposition of calcium carbonate?


  CaCO₃ (+ HEAT) → CO₂ + CaO
• What are some everyday uses of endothermic reactions?


  Used in sports injury packs to cool without a freezer
• What does the prefix "exo" mean in exothermic reactions?


  It means "exit," indicating heat is given out
• What does the prefix "endo" mean in endothermic reactions?


  It means "enter," indicating heat is taken in
• What are the key differences between exothermic and endothermic reactions?


  • Exothermic reactions release energy to the surroundings, indicated by a rise in temperature.
  • Endothermic reactions absorb energy from the surroundings, indicated by a fall in temperature.
• What are some examples of exothermic reactions and their applications?


  • Combustion of fuels (e.g., burning wood)
  • Neutralization reactions (e.g., acid + alkali)
  • Oxidation reactions (e.g., sodium in water)
  • Applications: hand warmers, self-heating cans
• What are some examples of endothermic reactions and their applications?


  • Reaction between citric acid and sodium hydrogencarbonate
  • Thermal decomposition (e.g., calcium carbonate)
  • Applications: sports injury packs
• What are the two types of reactions discussed in this topic?

  Exothermic and Endothermic reactions
• What happens in an exothermic reaction?


  Heat is given out
• What occurs in an endothermic reaction?


  Heat is taken in
• What is an example of an exothermic reaction?


  Burning
• How can you measure energy transfer in a chemical reaction?


  • Measure initial temperature of reactants
  • Initiate reaction in a polystyrene cup
  • Measure final temperature of the solution
• What is the biggest problem when measuring energy changes in reactions?


  Energy loss to the surroundings
• How can you reduce energy loss during measurements?

  By insulating the polystyrene cup with cotton wool and using a lid
• What types of reactions can the energy measurement method be used for?


  • Reactions between metals and acids
  • Reactions between carbonates and acids
• How can you investigate the effect of acid concentration on energy released in a neutralisation reaction?

  1. Prepare beakers with different concentrations of HCl and NaOH
  2. Use a water bath to equalize temperatures
  3. Mix in a polystyrene cup and measure temperature changes
• What is the first step in testing the effect of acid concentration on energy released?


  Put 25 cm³ of hydrochloric acid and sodium hydroxide in separate beakers
• What does a reaction profile diagram show?


  The relative energies of reactants and products and energy changes during the reaction
• In an exothermic reaction, where are the products in relation to the reactants on a reaction profile?


  The products are at a lower energy than the reactants
• What does the difference in height on a reaction profile represent?


  The overall energy change in the reaction per mole
• What does activation energy represent in a reaction?


  The minimum amount of energy needed for reactants to collide and react
• How does the activation energy affect the reaction?


  The greater the activation energy, the more energy needs to be supplied
• In an endothermic reaction, where are the products in relation to the reactants on a reaction profile?


  The products are at a higher energy than the reactants
• What is a common misconception about energy in exothermic reactions?


  That the reaction mixture gets warmer while the particles lose energy
• What is the equation for the combustion of methane in air?


  CH₄ + 2O₂ → CO₂ + 2H₂O