Energy changes in chemical reactions

• What can be observed during a chemical reaction?

  Changes in energy and temperature
• What happens to objects near a bonfire?

  They become warmer due to heat transfer
• What type of reactions are exothermic reactions?

  Reactions that transfer energy to surroundings
• How is energy usually transferred in exothermic reactions?

  As heat energy to the surroundings
• What is a common method to detect temperature increase in exothermic reactions?

  Using a thermometer
• What is neutralisation in chemistry?

  Reaction between an acid and a base
• What is an acid in chemistry?

  Corrosive substance with pH lower than 7
• What is an alkali in chemistry?

  Base that is soluble in water
• What happens in an endothermic reaction?

  Energy is taken in from the surroundings
• How does an endothermic reaction affect temperature?

  Causes the reaction mixture to become colder
• What is a common method to detect temperature decrease in endothermic reactions?

  Using a thermometer
• What is thermal decomposition?

  Breakdown of a compound when heated
• How does the temperature change in an exothermic reaction compared to an endothermic reaction?

  Exothermic reactions increase temperature, endothermic decrease
• What is the result of mixing sodium hydroxide with hydrochloric acid?

  Produces sodium chloride and water
• What happens when sodium carbonate is mixed with ethanoic acid?

  Produces sodium ethanoate, water, and carbon dioxide
• What can be classified as exothermic or endothermic reactions?

  Changes in energy during chemical reactions
• How can energy changes in chemical reactions be observed?

  By examining changes in chemical bonding
• What happens to bonds during a chemical reaction?

  • Bonds in reactants are broken
  • New bonds are formed in products
• What is the process of breaking bonds called?

  Bond-breaking
• Is bond-breaking an endothermic or exothermic process?

  Endothermic process
• What is released when new bonds form?

  Energy
• What type of process is bond-making?

  Exothermic process
• What determines if a reaction is endothermic or exothermic?

  The difference in energy for breaking and making bonds
• What indicates an exothermic reaction in terms of heat energy?

  More heat energy is released when making bonds
• What indicates an endothermic reaction in terms of heat energy?

  More heat energy is absorbed when breaking bonds
• What do energy diagrams show in chemical reactions?

  • Level of energy of reactants
  • Level of energy of products
  • Difference in energy indicates energy change
• In an exothermic reaction, where are the reactants in relation to the products?

  Higher than the products
• In an endothermic reaction, where are the reactants in relation to the products?

  Lower than the products
• What is the enthalpy change (∆H) in an exothermic reaction?

  Always negative
• What is the enthalpy change (∆H) in an endothermic reaction?

  Always positive
• What is activation energy?

  The minimum energy required for a reaction
• How is activation energy represented on an energy profile?

  • Shown as a 'hump'
  • Indicates energy needed for reactants to react
• How does activation energy differ between exothermic and endothermic reactions?

  Both require activation energy to proceed
• What can be classified as exothermic or endothermic reactions?

  Changes in energy during chemical reactions
• What is bond energy?

  • Energy needed to break one mole of a bond
  • Measured in kJ/mol
• How do you calculate the energy change in a reaction?

  Energy change = energy in – energy out
• What is a reactant?

  A substance that reacts to form products
• What is a product?

  A substance formed in a chemical reaction
• What does a negative energy change indicate?

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

  The temperature increases as energy is released