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Module 5 - Chapter 18 - Rates of reaction I - Coggle Diagram
Module 5 - Chapter 18 - Rates of reaction I
Rate of reaction
Order of reaction
Rate of reaction is proportional to concentration of particular reactant raised to a power
Power is the order of reaction for that reaction
Zero order
When concentration of reactant has no effect on the rate, reaction is zero order with respect to the reactant
Increasing concentration of A doesn't affect rate
First order
Rate depends on the reactant concentration raised to the power of one
If concentration of A is doubled, rate increases by a factor of two
Second order
Rate depends on the reactant concentration raised to the pwoer of two
If concentration of A is doubled, reaction rate increases by a factor of 4
Orders from experiments
Orders of reaction have to be determined experimentally and cannot be found from the chemical equation
Rate must be measured after the same time, ideally as close to the start time
unit =
Rate equation
Rate equation gives mathematical relationship between concentrations of reactants and reaction rate
Overall order = sum of orders with respect to each reactant
Rate constant
Rate constant is the consant that converts between the rate of reaction and concentration and ords
Units
Depends on number of concentraiton terms in the equation
To find units
Rearrange equation to make k the subject
Substitue units in
Cancel common units
Constant when the reaction temperature is constant
Continuous monitoring of rate
Concentration time graphs can be plotted from continuous measurements taken during a reaction
Colorimeter
Wavelength of the light passing through a coloured solution is controlled using a filter
Intensity of light passing through the sample is measured
Filter is chosed so that the complementary colour to the colour being absorbed
Aborbance is recorded, which is proportional to concentration of the solution
A calibration curve is generated
Concentration-time graphs
Zero order
Straightline with negative gradient
Gradient equals to the rate constant
First order
Downard curve with decreasing gradient over time
Time for the concentration for the reatant to halve is constant
Second order
Downard curve
Steeper at start
Half life
Time taken for initial concentration of the reaction to decrease by half
First order reactions have a constant half-life with the concentration halving every half life
Measure successive half lives, if they are the same, the reaction is first order
Determining k for a first order reaction
Rate constant from rate
Tangent to the curve is drawn at a particular concentration, the gradient gives the rate of reaction
Rearrange the rate equation and substitute the value of rate and the concentration
Half life
Use the exponentational relationship for a constant half-life
