3.1.9 Rate Equations Flashcards
How is the rate of chemical equations related to the concentration of reactants?
Rate = k [A]^m [B]^n
Define rate
A change in concentration of reactant/product over time
What affects the rate constant?
Temperature
How is the order of reaction found?
Experimentally
What does zero order mean?
The reactant has no effect on the rate of reaction
How is overall order calculated?
Add the orders of all reactants
What is the rate determining step? (2)
The slowest step of a reaction, therefore limiting the rate of reaction
The step involving the molecules found in the rate equation
How is an initial rates method used to determine the order of a reaction? (5)
Carry out reaction, monitoring its progress to collect concentration data at different times
Plot a concentration-time graph
Repeat experiment with a different initial concentration of one reactant and draw another graph
Use a tangent at t=0 to determine the initial rate for each reaction
Compare the initial rates to determine how the change in concentration affected the rate of reaction
How do clock reactions allow the initial rate to be estimated? (3)
Measure how the time taken for a set mount of product to form changes as the concentration of different reactants is changed
As the limiting reactant is used up, there is an easily observable endpoint (e.g. colour change)
The quicker the reaction finishes, the faster the initial rate is
What assumptions do clock reactions rely on? (3)
The concentration of each reactant does not change significantly
Temperature is constant
When endpoint is seen, the reaction has not proceeded too far
Concentration-time graphs - zero order
Constant negative gradient
Concentration-time graphs - first order
Negative curve
Concentration-time graphs - second order
Steep negative curve
Rate-concentration graphs - zero order
Horizontal gradient
Rate-concentration graphs - first order
Straight line through origin
