CI - Rates and reaction mechanisms Flashcards
What is the rate-determining step of a reaction?
The slowest step in a multi-step reaction.
What is the slowest step in a multi-step reaction called?
The rate-determining step.
How many steps can reaction mechanisms have?
One step or a series of steps.
What is different about the rate for a reaction with a series of steps?
Each step can have a different rate.
What step is the overall rate decided by in a reaction mechanism?
The slowest step - the rate-determining step.
What is the rate-determining step also known as?
The rate-limiting step.
What in the rate equation affects the rate?
Reactants.
How do you work out which reactants are involved in the rate-determining step from the rate equation?
- If the reactant appears in the rate equation, it must affect the rate. So this reactant. or something derived from it, must be in the rate-determining step.
- If a reactant doesn’t appear in the rate equation, then it isn’t involved in the rate-determining step (and neither is anything derived from it).
What are the important points to remember about rate-determining steps and mechanisms?
1) The rate-determining step doesn’t have to be the first step in a mechanism.
2) The reaction mechanism can’t usually be predicted from just the chemical equation.
Apart from the reactants, what else can appear in the rate equations and what does this mean they can be in too?
Catalysts - so they can be in the rate-determining steps too.
What can you predict from the rate-determining step?
The rate equation.
What does the order of a reaction with respect to a reactant show?
The number of molecules of that reactant which are involved in the rate-determining step.
How can you predict the rate equation from the rate-determining step?
The order of a reaction with respect to a reactant shows the number of molecules of that reactant which are involved in the rate-determining step.
What can you predict from the rate equation?
The mechanism for the reaction.
Why do you have to take care when suggesting a mechanism?
Things might not always be what they seem. For example, there might look like there are two of the same molecules reacting together so you might predict that the reactant is second order when experimentally it may be found to be first order. Therefore it shows that there is only one molecule of the reactant reacting in the rate-determining step.
