Topic 5 : energy changes

• What is needed to break chemical bonds in a reaction?

  Energy
• What happens when chemical bonds form?

  Energy is released
• What indicates a net energy release in a reaction?

  More energy released than needed
• What type of reaction is characterized by a temperature increase?

  Exothermic reaction
• How can explosions be classified in terms of energy transfer?

  They are exothermic reactions
• What is an endothermic reaction characterized by?

  Net energy input into the reaction
• What is the procedure for measuring temperature changes in a neutralization reaction?

  • Use a polystyrene cup
  • Insulate the cup
  • Insert a thermometer through the lid
  • Measure maximum temperature reached
  • Increase alkali volume and repeat
  • Observe temperature plateau due to acid depletion
• What does the meeting point of two best fit lines represent in the temperature experiment?

  Amount of alkali needed to neutralize acid
• How do potential and kinetic energy relate in chemical reactions?

  • Potential energy decreases, kinetic energy increases
  • Balancing act: one goes down, the other goes up
  • Exothermic reactions result in increased kinetic energy
• What is the activation energy in a reaction?

  Energy needed to start the reaction
• How much energy is needed to break a carbon-hydrogen covalent bond?

  $413 \text{ kJ/mol}$
• What is the total energy needed to break all bonds in the combustion of methane?

  $2642 \text{ kJ/mol}$
• How much energy is released when bonds are formed in the combustion of methane?

  $3466 \text{ kJ/mol}$
• What is the net energy released in the combustion of methane?

  $824 \text{ kJ/mol}$
• What are the basic components of a battery?

  • Two different metals
  • An electrolyte
  • Potential difference to power devices
• What happens to non-renewable batteries when reactants are used up?

  They stop working
• How do rechargeable batteries function?

  Reverse reaction occurs with supplied current
• How is hydrogen produced for fuel cells?

  By splitting water through electrolysis
• What happens when hydrogen and oxygen recombine in fuel cells?

  A voltage is produced