Exothermic and Endothermic

• What happens to energy during chemical reactions?


  Energy is conserved.
• What does it mean that the amount of energy in the universe is the same at the beginning and the end of a reaction?


  It means energy is neither created nor destroyed in a reaction.
• What occurs to the energy of product molecules in an exothermic reaction?


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


  An exothermic reaction transfers energy to the surroundings.
• How does an exothermic reaction affect the temperature of the surroundings?


  The temperature of the surroundings increases.
• What are some examples of exothermic reactions?


  Combustion, many oxidation reactions, and neutralisation.
• What are everyday examples of exothermic reactions?


  Self-heating cans and hand warmers.
• What is an endothermic reaction?


  An endothermic reaction takes in energy from the surroundings.
• How does an endothermic reaction affect the temperature of the surroundings?


  The temperature of the surroundings decreases.
• What is a common application of endothermic reactions?


  Some sports injury packs are based on endothermic reactions.
• What are examples of endothermic reactions?


  Thermal decomposition and the reaction of citric acid and sodium hydrogencarbonate.
• What is required for chemical reactions to occur?


  Reacting particles must collide with each other with sufficient energy.
• What is activation energy?


  Activation energy is the minimum amount of energy that particles must have to react.
• What can reaction profiles show about chemical reactions?


  • Relative energies of reactants and products
  • Activation energy
  • Overall energy change of a reaction

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


  You can tell by looking at whether the reactants or products have more energy.

  
• What characterizes an exothermic reaction in terms of energy transfer?


  Heat is released to the surroundings, so products have less energy than reactants.
• What characterizes an endothermic reaction in terms of energy transfer?


  Heat is taken in from the surroundings, so products have more energy than reactants.
• What happens to energy when bonds in reactants are broken?


  Energy must be supplied to break bonds in the reactants.
• What happens to energy when bonds in products are formed?


  Energy is released when bonds in the products are formed.
• How can the overall energy change of a reaction be calculated?


  By subtracting the sum of energy released to form bonds from the sum of energy taken in to break bonds.
• What indicates an endothermic reaction in terms of energy change?


  Energy taken in to break bonds is greater than energy released when formed.

  
• What indicates an exothermic reaction in terms of energy change?


  Energy taken in to break bonds is less than energy released when formed.