Introduction to reaction profiles
reaction progress with time
A reaction profile shows the variation in energy when reactants come together, form the activated complex known as the transition state, which then results in products.
The difference in energy between reactants and the transition state is known as the activation energy. The activation energy for a particular reaction depends on the nature of bond-breaking and bond making that occurs in conversion from reactants to transition state. Reactions that have lower activation energies are faster irrespective of whether they are exothermic or endothermic
The difference in energy between reactants and the transition state is known as the activation energy. The activation energy for a particular reaction depends on the nature of bond-breaking and bond making that occurs in conversion from reactants to transition state. Reactions that have lower activation energies are faster irrespective of whether they are exothermic or endothermic
A catalyst is a substance that speeds up the rate of reaction without being consumed by the reaction.
One way in which catalysts increase the rate of reaction is by forming a complex with one reactant. This complex that reacts by a lower activation energy pathway than the reactant itself.
Thus if a reaction is viewed as a stepwise process, a catalyst is a reactant in the first step and a product in the second step as shown below. H+ catalyses the reaction but does NOT appear in the overall equation because it is consumed in one state and formed in a second step.
Step 1: CH3CH2OH + H+
CH3CH2OH2+
Step 2: CH3CH2OH2+ CH2=CH2 + H2O + H+
Overall: CH3CH2OH CH2=CH2 + H2O
Thus if a reaction is viewed as a stepwise process, a catalyst is a reactant in the first step and a product in the second step as shown below. H+ catalyses the reaction but does NOT appear in the overall equation because it is consumed in one state and formed in a second step.
Step 1: CH3CH2OH + H+
CH3CH2OH2+Step 2: CH3CH2OH2+
CH2=CH2 + H2O + H+Overall: CH3CH2OH
CH2=CH2 + H2OHomogeneous catalysts are in the same phase as reactants.
In the reaction above, the reactant is a liquid, as is the added acid.
When they are mixed, you can not see the catalyst separate from the reactant.
When they are mixed, you can not see the catalyst separate from the reactant.
Heterogeneous catalysts are in a different phase to reactants.
Hetereogeneous catalysts are solids that do not mix with the reactants
An example is platinum metal which catalyses reaction of the gas H2 with the gas H2C=CH2..
Reaction with heterogeneous catalysts occurs on the surface of the catalyst.
An example is platinum metal which catalyses reaction of the gas H2 with the gas H2C=CH2..
Reaction with heterogeneous catalysts occurs on the surface of the catalyst.