# Kinetics

Rate equation

Graphs

Calculating constant, k

Experiments involving rate of reaction

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KINETICS
THINGS THAT EFFECT RATE OF REACTION...
There are FIVE things that affect the rate of reaction. These are:
1. Concentration of the reactants.
2. Pressure of the gases in the reactants and products.
3. Surface area of the reactants.
4. Catalysts added to provide an alternate route for the reaction to take place which
requires lower activation energy.
5. Temperature at which the reaction occurs.
The COLLISION THEORY says that rate is dependent on collision frequency and the
fraction with at least the required activation energy, such that:
This can be used to explain why the above factors affect the rate of reaction:
Changing the concentration of reactants, pressure of gases, surface area of
reactants or temperature of reactant mixture changes the COLLISION
FREQUENCY.
Despite the change in collision frequency having an effect on the rate of reaction
when the temperature of the reactant mixture is changed, the MAIN REASON for
a change in rate of reaction in this incidence is the increase in energy of the
molecules, so a HIGHER FRACTION WILL HAVE AT LEAST THE
ACTIVATION ENERGY.
Catalysts provide an alternate route with lower activation energy, so this also
means a HIGHER FRACTION OF MOLECULES WILL HAVE AT LEAST
THE ACTIVATION ENERGY.

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EFFECTS OF CONCENTRATION ON THE RATE OF REACTION...
This is shown by the experimental rate equation:
In explanation to this equation:
K is the rate constant provided the reactions take place at a CONSTANT
TEMPERATURE.
[A] and [B] are the concentration of solutions A and B.
X and y are the orders (powers) of the reaction with respect to [A] and [B].
The OVERALL ORDER is the sum of x and y.

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ORDERS OF TWO...
When rate is plotted against [A], the graph will show a PARABOLA that GOES
THROUGH THE ORIGIN.
When [A] is plotted against time, the graph will show a RECTANGULAR HYPERBOLA
(an exponential curve that comes closer to the axis).
HALF LIFE...
The half life (t ½ ) is the time taken for the initial concentration of a reactant to half.
It can be used to CALCULATE THE ORDER of reactants using a graph where [A] is

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EXPERIMENTAL METHODS...
These can be either non-interfering or interfering methods. Non-interfering methods of
collecting data are better to use than interfering methods.
NON-INTERFERING METHODS...
1. COLORIMETERS can be used to measure the change in colour intensity of
coloured solutions. The results collected can be shown as a CALIBRATION
CURVE, where absorbance is plotted against [A].
2. CHANGES IN GAS VOLUME can be used either with a gas product or gas
reactant and product. A gas syringe is used to measure the change in gas volume.…read more

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ANALYSING RESULTS FROM EXPERIMENTAL METHODS...
The INITIAL RATE METHOD uses the fact that all the concentrations of reactions
are known at the start of the reaction because they are what you put in.
FOR ORDER 0, the rate stays the same regardless of change of concentration.
FOR ORDER 1, the rate change is equal to the change in concentration e.g. both x2.
FOR ORDER 2, the rate change is unequal to the change in concentration.…read more