M5 Chapter 18 - Rates of Reaction Flashcards
(31 cards)
Define the rate of reaction.
The change in concentration of a reactant or a product per unit time.
At a given instant, how could you calculate the rate of reaction?
Rate of reaction = change in conc of reactants or products / time (gradient)
If the order is zero with respect to a reactant, what does that mean?
Changing the concentration of the reactant has no effect on the rate.
What is the effect on rate in a first order reaction?
Rate is directly proportional to the concentration of the reactant.
What is the effect on rate in a second order reaction?
Change in rate = change in concentration squared.
Write a generic rate equation and state what each term means.
Rate = k[X]ˣ[Y]ʸ
Where k = rate constant for the reaction.
[X] and [Y] are concentrations of species X and Y respectively x and y are the orders of reaction with respect to X and Y.
Do zero order reactants appear on rate equation? Why?
No because they have no effect on the rate.
How is the overall order of a reaction calculated?
Sum of the individual orders.
How would you calculate the units of the rate constant?
Units of rate are moldm-3s-1 and units of concentration are moldm-3. Hence, rearrange to get k = … Then sub in the units and cancel them out.
When the overall order is 3, what would be the units for rate constant.
mol-2dm6s-1.
How could you measure the rate of reaction experimentally? (Different methods)
Use a colorimeter at suitable intervals if there is a colour change.
If gas is involved, use a gas syringe to collect volume of gas evolved, or measure the change in mass of reaction mixture.
What does half life mean?
The time taken for concentration of a reactant to decrease by half.
What is the symbol for half life?
t 1/2.
Draw a concentration time graph for a zero order reactant.
constant negative gradient with conc on y and time on x.
Draw a concentration time graph for a first order reactant.
looks like reciprocal graph.
What is the relationship between first order reactions and half life?
First order reactants have a constant half life.
What is the equation that is used to determine rate constant using half life in a first order reaction?
k = ln2/t 1/2
How would you draw a rate concentration graph?
Plot [A] against time, draw tangents at different values –> draw a secondary graph of rate against [A].
What is the relationship between rate and time?
Rate is proportional to 1/t.
Draw a rate concentration graph for a zero order reactant.
Straight line of y = 3 for example.
Draw a rate concentration graph for a first order reactant.
graph of y=x
Draw a rate concentration graph from a seconda order reactant.
y= x squared
How to determine the rate constant from a rate concentration graph of first order?
k = rate/concentration.
What is the rate determining step?
The slowest step in a reaction with multiple steps.
