Exothermic and endothermic reactions

• What is conserved in chemical reactions?

  Energy
• What happens to the total amount of energy in the universe after a chemical reaction?

  It remains the same
• What is an exothermic reaction?

  Energy is transferred to the surroundings
• What happens to the temperature of the surroundings during an exothermic reaction?

  It increases
• What are examples of exothermic reactions?

  • Combustion reactions
  • Many oxidation reactions
  • Most neutralisation reactions
• What are everyday uses of exothermic reactions?

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

  Energy is taken in from the surroundings
• What happens to the temperature of the surroundings during an endothermic reaction?

  It decreases
• What are examples of endothermic reactions?

  • Thermal decomposition reactions
  • Reaction of citric acid and sodium hydrogencarbonate
• What is an everyday use of endothermic reactions?

  Instant ice packs for sports injuries
• What does an energy level diagram show about a reaction?

  It shows if the reaction is exothermic or endothermic
• What happens to energy in an exothermic reaction?

  Energy is given out to the surroundings
• How does the energy level change in an exothermic reaction?

  The energy level decreases
• What does a downwards arrow in a reaction profile indicate?

  Energy is given out
• What happens to energy in an endothermic reaction?

  Energy is taken in from the surroundings
• How does the energy level change in an endothermic reaction?

  The energy level increases
• What does an upwards arrow in a reaction profile indicate?

  Energy is taken in
• Why is a reaction profile more useful than an energy level diagram?

  It describes how energy changes during the reaction
• What does a reaction profile include that is crucial for reactions?

  Activation energy
• What is activation energy?

  The minimum energy needed for a reaction
• How is activation energy represented in a reaction profile?

  As a 'hump' in the line
• What does the height of the 'hump' in a reaction profile represent?

  The difference in energy between reactants and the top of the hump
• How is the overall change in energy in a reaction calculated?

  Difference between reactants and products energy
• What does a reaction profile for an exothermic reaction show?

  A decrease in energy level
• What does a reaction profile for an endothermic reaction show?

  An increase in energy level
• What are the key features of a reaction profile?

  • Shows energy changes during a reaction
  • Includes activation energy as a 'hump'
  • Indicates whether the reaction is exothermic or endothermic
• How can you determine if a reaction is exothermic or endothermic from a reaction profile?

  • Exothermic: Energy level decreases
  • Endothermic: Energy level increases
• What happens to energy when bonds are broken or formed?

  Energy is transferred
• What type of process is breaking bonds?

  Endothermic
• What type of process is forming bonds?

  Exothermic
• What happens to heat energy during an endothermic reaction?

  Heat energy is taken in
• What happens to heat energy during an exothermic reaction?

  Heat energy is given out
• What occurs to bonds in reactants during a chemical reaction?

  Bonds in the reactants are broken
• What occurs to bonds in products during a chemical reaction?

  New bonds are made in the products
• What determines the type of reaction in terms of energy changes?

  The difference in energy for bonds broken and made
• When is a reaction considered exothermic?

  If more heat energy is released than taken in
• When is a reaction considered endothermic?

  If less heat energy is released than taken in
• What is the method to calculate energy changes in a reaction?

  Using bond energies
• What is a bond energy?

  Energy needed to break one mole of a bond
• How do different bonds relate to bond energies?

  Different bonds have different bond energies