These are detailed Revision Notes for Topic 1.9 of AQA A-Level Chemistry (Rate Equations). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- The rate of chemical equations
- The rate e...
Kinetics
18.1 The Rate of Chemical Reactions:
18.1 The rate of chemical reactions
- The rate of a reaction is the change in concentration of
any of the reactants or products with unit time. 18.2 the rate expression and order of reaction
- The rate at any particular point on the graph is worked 18.3 determining the rate equation
out by drawing a tangent and then calculating the
gradient of the tangent. 18.4 the Arrhenius equation
- Reaction rates are measured in moldm-3s-1. 18.5 the rate-determining step
18.2 The Rate Expression and Order of Reaction:
- The rate expression tells us about the contributions of the species of affecting the reaction rate.
- The rate expression can only be determined by experimentation.
- k is the rate constant; it is different for every reaction, and it varies with temperature.
- Not all rates are directly proportional to the concentration of the substance. Some are proportional to
the square of the concentration, and some are not dependent on the concentration at all.
- This is represented in a rate equation by the order of the reaction.
- The order of the reaction is the power that the concentration has to be raised to to fit the rate
equation.
- The overall order of the reaction is the sum of orders for each species.
- Zero order
o The rate of reaction is not dependent on the concentration
o Rate = k[X]0 or rate = k
- First order
o The rate of reaction is directly dependent on the concentration
o Rate = k[X]1 (usually the 1 isn’t shown) Rate = k[X]
- Second order
o The rate of reaction is dependent on the concentration squared
o Rate = k[X]2
- The units are calculated in the same way that Kc and Kp units are
18.3 Determining the Rate Equation:
- Plot a graph of concentration vs time
o Zero order ~ straight line
o 1st or 2nd order ~ Curve
- Plot a graph of rate vs concentration
o Zero order ~ horizontal line
o 1st order ~ straight ascending line
o Possibly 2nd order ~ Curve
- To confirm a 2nd order, you can plot rate vs the square of the concentration
o 2nd order ~ Straight line
- Initial rate method:
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