Unit 4 Flashcards
What is the formula for the overall rate of reaction
R = change in concentration/change in time
What is the unit for rate
mol dm^-3 s^-1
What are the ways to measure rate of reaction
Titration
Colorimetry
Change in volume of gas
Electrical conductivity
Pressure
What do rate equations show
The mathematical relationship between rate and concentration
What is the relation between rate and concentration
They are directly proportional to each other
What does k represent
k is the rate constant
When is k a constant
At a specific temperature
How can rate equations be found
Rate equations can only be determined and cannot be found theoretically
What are the units of k in a zero order reaction
mol dm^-3 s^-1
What are the units of k in first order reaction
s^-1
What are the units of k in a second order reaction
mol^-1 dm^3 s^-1
What is the rate determining step
The slowest step in a multistep reaction mechanism
Determining rate order from a graph
There are two ways of determining rate order from a graph
1. Continuous method
2. Initial rate method
What is the continuous method
One reaction mixture where samples are taken at regular intervals the sample is quenched and the concentration of a reactant or product is found by titration, to generate data to enable concentration-time or volume-time graphs to be plotted.
What are the steps to find rate order using the continuous method
- Draw a concentration time graph
- Find the half-life of the reaction at different concentrations
What is half-life
The time taken for the concentration of a reactant to fall to its original value
When half-life is constant…
The reaction is first order with respect to the reactant
If half-life doubles as the reaction proceeds then…
The reaction is second order with respect to that reactant
Half-life decreases for…
A zero order reaction
What is the exam answer for half-life
The half life is almost constant. Each half life is _____ seconds apart
What is the initial rates method
Several runs of the experiment are carried out, changing the concentration of one reagent. The time taken for a certain amount of product to be produced.
How to find rate at which product is produced from initial rate method
Rate = 1/T
What is the graph that is plotted for the initial rates method
Rate at which the product is formed against the concentration
What does a zero order reaction look like on the initial rates method graph
A straight line parallel to the x axis
What does a first order reaction look like on the initial rates method graph
A straight line going through the origin
What does a second order reaction look like on the initial rates method graph
A curved line going through the origin and increasing
when is titration used
when is colorimetry used
when is change in mass used
how is change in volume of gas measured
using a gas syringe or collecting it over water
when is electrical conductivity used
when is pressure used and how is it measured
nanometer
what is the formula for the acid-catalysed iodination of propanone?
CH₃COCH₃ + I₂ + (H^+(catalyst)) → CH₃COCH₂I + 2(H^+) + (I^-)
what is the rate equation of the acid-catalysed iodination of propanone?
Rate = k[CH₃COCH₃][H^+]
