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 an increase in temperature?

  Exothermic reaction
• What is an example of an exothermic reaction?

  Combustion
• What does the 'X' in exothermic signify?

  Energy goes out
• What happens in an endothermic reaction?

  Net energy input causes cooling
• What is the procedure for measuring temperature 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
• Why does the maximum temperature stop increasing in the neutralization reaction?

  All acid reacts, energy shared across volume
• What do the lines at best fit represent in the temperature graph?

  Amount of alkali needed to neutralize acid
• What does an energy profile illustrate?

  • Difference in energies between reactants and products
  • Potential energy vs. kinetic energy balance
  • Activation energy required to start a reaction
• What happens to potential and kinetic energy in a reaction?

  One decreases while the other increases
• What indicates an exothermic reaction in terms of energy?

  Products have less potential energy than reactants
• What is activation energy?

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

  413 kJ per mole
• How much energy is released when a mole of carbon-hydrogen bonds is formed?

  Same as energy needed to break it
• What is the total energy needed to break all bonds in the combustion of methane?

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

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

  $824 \text{ kJ per mole}$
• What are the characteristics of batteries?

  • Contain chemicals for voltage production
  • Composed of two different metals and an electrolyte
  • Non-renewable batteries stop when reactants are used
  • Rechargeable batteries can reverse reactions
• How do hydrogen fuel cells produce voltage?

  By recombining hydrogen and oxygen
• What process splits water into hydrogen and oxygen?

  Electrolysis
• What happens when hydrogen and oxygen recombine in fuel cells?

  A voltage is produced
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