Introduction to reaction profiles
As the diagram shows, reactions proceeds from reactants to products through a transition state that is higher in energy than either reactants or products.
Reaction systems may release energy to the surroundings or consume energy from the surroundings.
The amount of energy released or consumed depends on the difference in energy between reactants and products.
Exothermic reaction systems (as in the diagrams)
release heat energy to the surroundings, and
products are of lower energy than reactants.
products are of lower energy than reactants.
Endothermic reaction systems
consume heat energy from the surroundings and
the products are of higher energy than the reactants.
the products are of higher energy than the reactants.
The reaction energy is the difference between the energy of reactants and products.
The reaction energy is usually called reaction heat or the reaction enthalpy.
Exothermic reactions have negative reaction enthalpies (release heat).
Endothermic reactions have positive reaction enthalpies (consume heat).
Exothermic reactions have negative reaction enthalpies (release heat).
Endothermic reactions have positive reaction enthalpies (consume heat).
The activation energy is the difference in energy between the reactants and the transition state.
Reactants must collide with an energy exceeding the activation energy for reaction to occur.
For reaction to occur, an activated complex known as the transition state must form.
For reaction to occur, an activated complex known as the transition state must form.