C18 Rates Of Reactions Flashcards
Define rate of reaction
Change in conc 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
If the order is zero with respect to a reactant, what does that mean
Changing the conc of the reactant has no effect on the rate
What’s the effect on rate in a first order reaction
Rate is directly proportional to the conc
What’s the effect on rate in a second order reaction
Change in rate = change in conc squared
Do zero order reactants appear on rate equation? Why?
No, because they don’t have an effect on the rate
How’s the overall order of a reaction calculated
Sum of individual orders
How would you calculate the units of the rate constant
Units of rate are mol dm^-3 s^-1 and units of concentration are mol dm^-3
Rearrange rate equation to get k = sub units and cancel them out
When the overall order is 3, what’s would be the units for rate constant
dm^6 mol^-2 s^-1
How could you measure the rate of reaction experimentally (diff methods)?
Use a colorimeter at suitable intervals if there is a colour change
If gas is evolved, use a gas syringe to collect vol of gas evolved, or measure the change in mass of the reaction mixture
What does half life mean
The time taken for concentration of reactant to decrease by half
What’s the symbol for half-life
t1/2
What’s the relationship between first order reactions and half-life
First order reactants have constant half life’s
What’s the equation that’s used to determine rate constant using half-life in a first order reaction
k = ln2/t1/2
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’s the relationship bewteen rate and time
Rate is proportional to 1/t
How to determine the rate constant from a rate concentration graph of first order
k = rate/concentration
What is rate determining step
The slowest step in a reaction with multiple steps
How does the rate determining step link to the species involved in the rate equation
Any species involved in the rate determining step appear in the rate equation. Species only involved after the rate determining step do not appear in the rate equation
For a reactant in the rate equation, what indicates how many molecules of that reactant are involved in the rate determining step
The order of the reactant
The rate equation of a reaction is rate = k[NO]^2. How many molecules of NO will be present in the rate determining equation
2
What affects the value of the rate constant for a given reaction
Temperature, nothing else
What’s the effect of a 10*C temperature increase on the rate of reaction, roughly
Doubles rate of reaction
How can you invert the Arrhenius equation into a useful form for plotting a graph
Lnk = -Ea/RT + lnA
Graph of lnk against 1/T is a straight line:
Gradient = -Ea/R and y intercept is lnA
