Calorimetry

• Different chemicals store different amounts of energy in their bonds
• Example: Methane plus oxygen forming carbon dioxide and water
• Reactants have more total energy compared to products
• Reaction profile:

  • Y-axis: total energy of molecules
  • X-axis: progress of the reaction
  • Reactants on the left, products on the right
  • Products are placed lower down because they have less energy
• Energy released in a reaction is transferred to the surroundings

  • Energy cannot be created or destroyed, only transferred
  • Common way to exchange energy with surroundings is in the form of heat
• Exothermic reactions transfer energy to the surroundings

  • Most common type: combustion reactions
  • Other examples: neutralization reactions, oxidation reactions
• Endothermic reactions take in heat energy from the surroundings

  • Example: Breaking down calcium carbonate into calcium oxide and carbon dioxide
• Activation energy is the minimum energy needed for reactant particles to collide and react

  • Greater activation energy requires more energy to start the reaction
• Activation energy on reaction profiles:

  • Curve from reactants to products shows energy changes
  • Increase in energy from reactants to highest point on curve is activation energy