enthalpy profile diagrams

• In a reaction, bonds are broken and then bonds are made. For bonds to be broken, energy is taken in from the surroundings and when bonds are formed, energy is given out. The overall energy change of the reaction depends on how much energy is transferred in these processes.

  When energy is taken in from the surroundings, the enthalpy change is positive. This is an endothermic reaction. When energy is released to the surroundings, the enthalpy change is negative. This is an exothermic reaction.
• Activation energy is the minimum energy required to start a reaction by breaking bonds in the reaction
• label the graph

  A) reactants

  B) products

  C) exothermic

  D) enthalpy change

  E) activation energy

  
• label the graph

  A) endothermic

  B) enthalpy change

  C) activation energy

  D) reactants

  E) products

  
• Enthalpy changes are shown on an enthalpy profile diagram. Activation energy is the

  difference between the reactants and the top of the hump on an enthalpy profile diagram and is

  represented by the symbol Eₐ.