5.1.1 - How fast Flashcards
Define the term rate of reaction.
The change in concentration of a reactant (or product) per unit time
Its usual unit is mol dm-3 s-1
Define the term overall order.
The sum of the powers of the concentration terms on the rate equation.
Define the term order of a reaction (with respect to a given reactant).
The power to which the concentrations of the reactants is raised in the rate equation.
Define the term rate constant.
A constant value that relates the rate of a reaction at a given temperature
to the concentrations of the reactants. For a first order reaction, this can be determined using
the relationship k = ln 2/t 1/2
Define the term half-life.
The time taken for the concentration of a reactant to half.
Define the term rate-determine step.
The slowest step of a reaction.
Write a general rate equation and label what each part means.
What does zero order mean ?
Changes in concentration has no effects on the rate.
What does first order mean ?
Changes in concentration has a proportional change on rate=
E.g if [A] doubles then rate doubles
What does second order mean ?
Changes in concentration has a squared proportional change on rate.
E.g if [A] doubles then rate quadruples.
Key note for orders.
Orders can only be determined from experimental data. You can’t work the out just by looking at an equation.
What do you understand about the effects of :
- Temperature
- Concentration
- Pressure
On the rate constant (K)
- Temperature : As temp increases so does the rate constant. As temp decrease the rate constant also decreases. Think of it like Rate of reaction and K are proportional, if the rate of reaction increases or decreases due to temp so will the rate constant (K).
- Concentration : No effects just like in Kp and Kc.
- Pressure : No effects just like in Kp and Kc.
Oddly worded question but if the value of K is larger then what is the effect on the rate of reaction.
- The rate of reaction would be faster if the value of ‘K’ is larger. Remember this for multiple choice questions.
What is the units for rate
mol dm-3 s-1
How do we calculate the rate constant in terms of rate and concentration ?
Just rearrange the normal rate equation. To make K the subject
When a reactant has 0 order do we include them in the rate equation ?
No, because they have no effect on the rate so will not be included.
If you do then just remember to put 0 as their power (The rate value will end up being the same value if you didn’t include them at all)
How do we calculate the rate of reaction from a graph ?
Draw a tangent ( if needed) and calculate the gradient.
Blurt everything you understand about the initial rates method (allery chem 34.12)
Doing several experiments where the initial rate is measured and the initial concentration of a reagent is changed (initial rates method), with all other concentrations kept constant.
Blurt everything you understand about the continuous rates experiment.
Remember : The other reagents must be in a large excess so they are effectively constant.
How would zero order look on a concentration-time graph
How would first order look on a concentration-time graph
How would second order look on a concentration-time graph
How can we distinguish between a first and second order graph.
Calculate the half life.
1st order = Half life is constant
2nd order = half life increases by roughly the same amount.
How would zero order look on a rate-concentration graph.
This explains zero order because changing concentration does not effect the rate of the reaction.
How would first order look on a rate-concentration graph.
This explains first order because the change in concentration is directly proportional to the rate. So changing the concentration changes the rate equally.
How would second order look on a rate-concentration graph.
This quadratic graph represents a second-order reaction, where the rate is proportional to the square of the concentration. This means that if the concentration doubles, the rate increases by a factor of four. The curved shape of the graph shows that as concentration increases, the rate increases more rapidly. This follows the rate equation: Rate = k[Concentration]².
Another oddly worded question but how does the concentration-time graph help with the rate-concentration graph.
To find the rate (for the rate-concentration graph) we need to uses the concentration-time graph to find the gradient (we can do this by drawing a tangent if needed).
Define the term half life ?
The time it takes for the concentration of the reactant to half.
What do we use half life to calculate ?
The rate constant (K) units = S-1
How do we calculate the rate constant using half life ?
symbol for half life t1/2
How would the rate-concentration graph look like with all the combined orders.
Using experimental data to work out the rate equation (step 4 ) and 41.22 allery chem
This is more practice than explains btw tho
Using experimental data to work out the rate equation when all the concentrations for one reactant is different(step 4 ) and 47.02 allery chem
Again more practice and less explanation.
Using experimental data to filling gaps in a table.
(Step 4) and 44.43 allery chem
Again this is more practice than explanation.
If a reaction mechanism has a series of steps, then the overall rate is dependent on ?
The rate of the slowest step
(RDS)
Constructing overall equations and rate equations from a series of mechanics (section 5) and 53.00 allery chem
Again more practice and less explanation.
Arrhenius - Using y=mx + c what would each component of this equation represent in the Arrhenius equation
Arrhenius equation
Rearrange the Arrhenius equation to make K the subject
Rearrange the Arrhenius equation to make Ea the subject
Rearrange the Arrhenius equation to make A the subject
Rearrange the Arrhenius equation to make T the subject
What happens to the rate constant as the activation energy decreases (gets smaller)
What happens to the rate constant as the temperature increases
How do we get rid of the ‘e’ part (the exponential next to the A in the Arrhenius equation)
How do we us a graph to calculate the Arrhenius constant ?
