Chapter 16 - Further Kinetics
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What 2 ways can rate of reaction be expressed?
How quickly the concentration of a product increases with time or how quickly the concentration of a reactant decreases with time
What is the common units of rate of reaction?
mol dm^-3 s^-1
What different methods can you use to follow rate of reaction?
• measuring the volume of a gas evolved • measuring the change in mass of a reaction mixture • monitoring the colour change of a reaction • measuring the change in concentration using a titration • measuring the change in pH of a solution
What are the two methods of measuring the volume of gas evolved?
• collection over water into a measuring cylinder - collection using a gas syringe
Which more precisely measures the volume of gas evolved, gas syringes or measuring cylinder?
Gas syringes
In what situation would it not really matter whether you use a gas syringe or measuring cylinder?
When a large volume of gas is being measured, the difference in the degree of measurement uncertainty becomes so small that either instrument is sufficiently precise
What is another way of measuring rate in a reaction in which a gas is evolved?
Measuring the decrease is mass as the reaction proceeds.
When is measuring the change in mass applicable and not applicable to measure rate of reaction?
This technique is most precise when the gas given off has a relatively high density e.g. carbon dioxide. However with a low-density gas such a hydrogen, the mass changes are so small that the measurement uncertainties become significant
What can you quantitatively measure colour with?
A colorimeter
How do you analyse rate of reaction by titration?
• Use a pipette to remove small samples (aliquots) from a reaction mixture • The reactions in the aliquot are then quenched (the reaction is stopped)
How are aliquots quenched?
The reaction can be stopped by adding another substance or slowed down to almost zero by immersing it in an ice bath