This is a summary of every learning objective (a-j) for Topic 6, CI on the OCR Chemistry B (Salters-Nuffield) specification. I have arranged my notes answering each objective, and have given definitions, equations, techniques, and other notes based on the textbook and my lessons.
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CHEMISTRY SPECIFICATION NOTES
OCR Chemistry Salters Nuffield B AS/A-Level
Key:
Definitions are in turquoise
Core practicals are in orange
Equations and tests/reactions in green
Topic 6: The Chemical Industry (CI)
Kinetics
(a) the terms: (i) rate of reaction
Rate is how quickly a quantity of something changes. The rate of a reaction is the rate at
which reactants are converted into products. It is useful to know rates of reaction for many
reasons. You might want to know changes of concentration to alter the rate of a reaction in
an industrial process. Knowing the rate of reaction can also give you information about the
reaction mechanisms.
To measure the rate of reaction, you need to be able to measure the rate at which one of the
reactants is used up, or the rate at which one of the products is formed. You can find the rate
of reaction in terms of change in property / time taken.
(ii) rate constant, including units and (iii) order of reaction (both overall and with respect to a
given reagent), use of ‘∝’ (iv) rate equations of the form: rate = k[A]m[B]n where m and n
are integers; calculations based on the rate equation; the rate constant k increasing with
increasing temperature
The rate equation of a reaction is rate = k[A]^m [B]^n. The A and B in brackets are the
concentration of the reactants. M and n are the orders of reaction.
You cannot predict the rate equation for a reaction from its balanced equation.
‘K’ is the rate constant. K increases if temperature increases.
(c) techniques and procedures for experiments in reaction kinetics; use of experimental data
[graphical methods (including rates from tangents of curves), half-lives of initial rates when
varying concentrations are used] to find the rate of reaction, order of a reaction (zero-, first-
or second-order), rate constant and construction of a rate equation for the reaction
- The order of the reaction must be found experimentally
- Variables must be controlled to ensure the initial concentration of only one
substance is changed at a time
, - Measurements must be taken at same temperature for all separate reactants
- Concentration of enzymes does not change
- A way to control change in concentration is to have a large excess so it does not
change significantly over the course of the reaction
A progress curve shows how the concentration of reactant or product changes over time.
The gradient of each tangent on the line gives the rate of reaction for a particular
concentration of the reactant/product.
(b) the use of given data to calculate half-lives for a reaction
The half-life of a reaction can be found using the progress curve of the reaction.
The progress curve is the amount of reactant used / product produced over time, generally in
seconds.
If the half-lives of the reaction are constant, then the reaction is first order. The half-life
means the time taken for half of the reactant to get used up. The half-life is constant
whatever the starting amount.
(d) the Arrhenius equation and the determination of Ea and A for a reaction, given data on
the rate constants at different temperatures
The Arrhenius equation is used when other variables such as temperature or presence of
catalysts change, because these would typically affect the rate of reaction.
A is also called the frequency factor. Both A, e, and R are constants. Ea and T are variables
which can change. It can be used to calculate the impact that changes of Ea and T have on
k, and therefore the impact on rate of reactions. T is used for the effect of temperature, and
Ea the effect of catalysts on rates of reaction.
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