Topic 5: Energy Changes

• What is activation energy?

  The minimum energy for successful particle collisions
• What type of batteries are alkaline batteries?

  Non-rechargeable
• What happens in non-rechargeable cells when reactants are used up?

  The chemical reactions stop
• What do batteries consist of?

  Two or more cells connected in series
• What do chemical cells produce?

  Electricity through chemical reactions
• What characterizes an endothermic reaction?

  It takes in energy from the surroundings
• How does the temperature of surroundings change in an endothermic reaction?

  The temperature decreases
• In an endothermic reaction, what is greater: energy needed to break bonds or energy released from forming new bonds?

  Energy needed to break bonds
• What characterizes an exothermic reaction?

  It transfers energy to the surroundings
• How does the temperature of surroundings change in an exothermic reaction?

  The temperature increases
• In an exothermic reaction, what is greater: energy released from forming new bonds or energy needed to break existing bonds?

  Energy released from forming new bonds
• What do fuel cells require as inputs?

  Fuel and oxygen or air
• What happens to the fuel in a fuel cell?

  It is oxidised electrochemically
• What does the overall energy change of a reaction represent?

  The difference in bond energies of reactants and products
• What can reaction profiles show?

  Relative energies of reactants and products
• What is the purpose of reaction profiles?

  To illustrate activation energy and overall energy change
• What can rechargeable cells do that non-rechargeable cells cannot?

  Be recharged by reversing chemical reactions
• What are the key differences between endothermic and exothermic reactions?

  • Endothermic: absorbs energy, temperature decreases
  • Exothermic: releases energy, temperature increases
• What are the definitions for higher tier only in this topic?

  • Activation energy
  • Endothermic reaction
  • Exothermic reaction
  • Reaction profile
• What are the definitions marked for separate sciences only?

  • Alkaline batteries
  • Battery
  • Chemical cells
  • Fuel cells
  • Rechargeable cells
• What happens to energy during chemical reactions?

  Energy is conserved
• What does it mean that energy is conserved in reactions?

  The total energy remains constant
• What happens to product molecules in an exothermic reaction?

  They have less energy than reactants
• What is an exothermic reaction?

  Transfers energy to the surroundings
• What effect does an exothermic reaction have on the surroundings' temperature?

  It increases the temperature
• Name an example of an exothermic reaction.

  Combustion
• What are everyday examples of exothermic reactions?

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

  Takes in energy from the surroundings
• What happens to the temperature of surroundings during an endothermic reaction?

  It decreases
• Give an example of an endothermic reaction.

  Thermal decomposition
• What is a common application of endothermic reactions?

  Sports injury packs
• What is required for chemical reactions to occur?

  Reacting particles must collide
• What is activation energy?

  Minimum energy needed for particles to react
• How can reaction profiles be used?

  To show energies of reactants and products
• How can you determine if a reaction is exothermic or endothermic from a reaction profile?

  By comparing energies of reactants and products

  
• What indicates an exothermic reaction on a reaction profile?

  Products have less energy than reactants
• What indicates an endothermic reaction on a reaction profile?

  Products have more energy than reactants

  
• What must be supplied to break bonds in reactants?

  Energy
• What happens when bonds in products are formed?

  Energy is released
• How can overall energy change be calculated?

  Energy to break bonds minus energy released