Explain what occurs in a substitution reaction and give an example of substitution reaction. explain why organic reactions are typically slower than inorganic reactions.

Substitution Reactions are those reactions in which one nucleophile replaces another nucleophile present on a substrate. These reactions can take place via two different mechanism i.e SN¹ or SN². In SN¹ substitution reactions the leaving group leaves first forming a carbocation and nucleophile attacks carbocation in the second step. While in SN² reactions the addition of Nucleophile and leaving of leaving group take place simultaneously. 

Example:
                        OH⁻  +  CH₃-Br     →     CH₃-OH  +  Br⁻

In above reaction,

                   OH⁻  = Incoming Nucleophile

                   CH₃-Br  =  Substrate

                   CH₃-OH  =  Product

                   Br⁻  =  Leaving group

Organic reactions are typically slower than ionic reactions because in organic compounds the covalent bonds are first broken, this breaking of bonds is a slower step, while, in ionic compounds no bond breakage is required as it consists of ions, so only bond formation takes place which is a quicker and fast step.