Module 5.1
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Define rate of reaction
The change in concentration of a reactant or product per unit of time
List ways in which we can measure the rate of reaction?
Measure the loss in mass Measure how fast a gas in produced Measure how long it takes for a solution to go cloudy Measure the pH change of a reaction Watch for colour change
When measuring a change in mass, what should you use?
A weighting scale
When measuring how fast a gas is produced, what should you use?
A gas syringe
When measuring how long it takes for colour change, what should you use?
Colourimetry
What is meant by order?
With respect to a reactant, the order is the power to which the concentration of a reactant is raised to in the rate equation
What 3 orders must we be aware of?
Zero order First order Second order
What does the concentration-time graph of a zero order reactant look like?
Straight line downards
What does the rate-concentration graph of a zero order reactant look like?
Straight line
With zero order reactants, what will happen to the rate, if the concentration of the reactant is changed?
Nothing
With zero order reactants, what pattern does its half-life follow?
DECREASES with time
What does the concentration-time graph of a first order reactant look like?
Slopes downwards
What does the rate-concentration graph of a first order reactant look like?
Straight line upwards
With first order reactants, what will happen to the rate, if the concentration of the reactant is changed?
The rate changes by a proportionally equal amount
With first order reactants, what pattern does its half-life follow?
Constant
What does the concentration-time graph of a second order reactant look like?
Slopes downwards
What does the rate-concentration graph of a second order reactant look like?
Slopes upwards (exponential growth)
With second order reactants, what will happen to the rate, if the concentration of the reactant is changes by X?
The rate will change by X^2
With second order reactants, what pattern does its half-life follow?
Increases with time
Define overall order
The sum of the orders of all the different reactants
If the overall order of a reaction is 0, what units does the rate constant have?
mol dm^-3 s^-1
If the overall order of a reaction is 1, what units does the rate constant have?
s^-1
If the overall order of a reaction is 3, what units does the rate constant have?
dm^3 mol ^-1 s^-1
If the overall order of a reaction is 4, what units does the rate constant have?
dm^6 mol ^ -2 s^-1