Final answer:
SN1 and E1 reactions usually compete and have a first order overall rate equation.
Step-by-step explanation:
The SN1 and E1 reactions have the same rate-determining step, so they usually compete. Tertiary substrates easily react by both SN1 and E1 mechanisms, while secondary substrates may or may not react by these mechanisms. For example, secondary alkyl halides do not react, but secondary alcohols and ethers do. Primary substrates generally do not undergo SN1 and E1 reactions.
The rate equation for SN1 and E1 reactions is first order overall. This means that the reaction rate is directly proportional to the concentration of the substrate. For SN1 and E1 reactions, doubling the concentration of the substrate will double the reaction rate.