Module 5.1 - Rates, equilibrium and pH - How fast? Flashcards
What is the reaction rate?
The change in the amount of reactants or products per unit time (normally per second).
What are a few methods you can use to find the rate of reaction?
> Measure the volume of gas produced.
Measure the loss in mass as a gas is produced.
Use colorimetry to measure the colour change of a reaction.
Measure the pH change of a reaction.
How can you find the rate at a given point on a concentration-time graph?
Draw a tangent on the curve and find the gradient of that (change in y/change in x).
Describe another method to estimate the initial rate of reaction?
Measure the time taken till there is an easily observable endpoint such as a colour change which tells you when the desired amount of product has formed. The quicker the endpoint is reached, the faster the initial rate of reaction.
How can you tell whether a reactant has 0,1 or 2 order of reaction?
If you double the reactant’s concentration -
>and the rate stays the same, the order with respect to that reactant will be 0.
>and the rate also doubles, the order with respect to that reactant is 1.
>and the rate quadruples, the order with respect to that reactant is 2.
What does the order of a reaction in respect to a particular reactant tell you?
Tells you how the reactant’s concentration affects the rate.
What is a reaction’s overall order?
This is the sum of the orders of all the different reactants.
Describe the rate equation and what each letter stands for?
Rate = k[A]^m[B]^n
k = rate constant
[A]/[B] - Concentration of A and B
m/n - The orders of reaction in respect to reactant A and and how the concentration of these reactants affects the rate.
Define half-life?
The time it takes for half of the reactant to be used up.
If you know the half life of a 1st order reaction, how can you work out the rate constant?
k = ln2/t1/2
What is the rate determining step (RDS)?
The slowest step in a multi-step reaction.
What is the rule for picking out which reactants from the chemical equation are involved in the RDS?
> If a reactant appears in the rate equation, it must affect the rate. So this reactant, or something derived from it, must be in the RDS.
What does the order of a reaction with respect to a reactant show about the RDS?
Shows the number of molecules of that reactant which are involved in the RDS.
What does each part of the arrhenius equation mean?
k = rate constant Ea = activation energy (J mol-1) T = temperature (K) R = gas constant (8.314 J K-1 mol-1) A = the pre-exponential factor
What happens to k as the activation energy gets bigger?
k gets smaller as Ea gets bigger. So a large Ea means a slow rate for if a reaction has a high activation energy then not many reactant particles will have enough energy to react. So only a few of the collisions will result in the reaction actually happening so the rate will be slow.
