Topic 16 - Kinetics II Flashcards
What is the reaction rate?
The change in the amount of reactants or products per unit time.
What are the different continuous monitoring methods of following the rate of a reaction?
- Gas volume
- Loss of mass
- Colour change
- Change in pH
- Titration
- Electrical conductivity
Remember to revise the different ways of following the rate of a reaction.
Pg 180 of revision guide
When continuously monitoring the volume of gas produced by a reaction, how can you work out the moles of a reactant at any point?
- Look at the volume of gas produced
- Use the ideal gas equation to work out how many moles of gas this is
- Use the molar ratios in the chemical equation to work out the moles/concentration of the reactant
When continuously monitoring the loss of mass in a reaction, how can you work out the moles of a reactant at any point?
- Use mole calculations to work out how much gas you’ve lost
* Use the molar ratios in the chemical equation to work out the moles/concentration of the reactant
What device is used to measure the colour change of a reaction?
Colorimeter
What does a colorimeter measure?
The absorbance of a solution.
When continuously monitoring the colour change in a reaction, how can you work out the moles of a reactant at any point?
- Plot a calibration curve of known values (absorbance values against concentration of the coloured solution)
- During the experiment, take a small sample from the reaction and read the absorbance
- Use the calibration curve to convert the absorbance to a concentration
When continuously monitoring the change in pH in a reaction, how can you work out the moles of a reactant at any point?
- Measure the pH
- Calculate the concentration of H⁺
- The rate can be calculated from this
When continuously monitoring a reaction, how can titration be used to work out the reaction rate?
- Small samples can be taken at regular intervals
- These can be titrated using a standard solution
- The rate can be found from measuring the change in concentration of the products or reactants over time
When can electrical conductivity be used to continuously monitor a reaction?
If the number of ions changes, so will the electrical conductivity.
How can a reaction rate be found from a concentration-time graph?
It is the gradient at any point.
When using a concentration-time graph to measure the reaction rate, what are the units?
moldm⁻³s⁻¹
What does the order of a reaction with respect to a given reactant tell you?
How the reactant’s concentration affects the rate.
What does it mean if the order of reaction with respect to reactant X is 0?
The rate is not affected by [X].
What does it mean if the order of reaction with respect to reactant X is 1?
The rate is proportional to [X].
What does it mean if the order of reaction with respect to reactant X is 2?
The rate is proportional to [X]².
If the rate of a reaction with respect to reactant X is 0, what happens to the rate if [X] doubles and triples?
- Doubles -> Rate stays the same
* Triples -> Rate stays the same
If the rate of a reaction with respect to reactant X is 1, what happens to the rate if [X] doubles and triples?
- Doubles -> Rate doubles
* Triples -> Rate triples
If the rate of a reaction with respect to reactant X is 2, what happens to the rate if [X] doubles and triples?
- Doubles -> Reaction is 4 times faster
* Triples -> Reaction is 9 tunes faster
Can orders of reaction be be worked out from a chemical equation?
No, but they can be worked out experimentally.
What two types of graph can be drawn in terms of orders of reactions?
- Concentration against time
* Rate against concentration graph
How can you construct a rate-concentration curve from a concentration-time graph of a reaction?
- Find the gradient of the concentration-time graph at multiple points
- This will give you a series of rates at various concentrations
- Plot each of these points on a new graph of rate against concentration
- Draw a line or curve of best fit
Describe the concentration-time graph for a 0 order reaction.
- Starts at positive y-intercept
- Straight line of negative gradient
(See diagram pg 182 of revision guide)