the energy change of reactions

• What must be supplied during a chemical reaction to break bonds in the reactants?

  Energy
• What happens to energy when bonds in the products are formed during a chemical reaction?

  Energy is released
• How can the energy needed to break bonds and the energy released when bonds are formed be calculated?

  From bond energies
• What does the overall energy change of a reaction represent?

  The difference between the energy needed to break bonds in reactants and the energy released when bonds in products are formed
• In an exothermic reaction, what is greater: the energy released from forming new bonds or the energy needed to break existing bonds?

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

  The energy needed to break existing bonds
• What are the key differences between exothermic and endothermic reactions?

  • Exothermic reactions:
  • Energy released from forming new bonds is greater than energy needed to break existing bonds.
  • Endothermic reactions:
  • Energy needed to break existing bonds is greater than energy released from forming new bonds.