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A2 Unit F325: Equilibria, Energetics
and Elements
Module 1: Rates Equilibrium and pH

How Fast?

Rates graphs and Orders
Rate of Reaction:
o Measures the rate of formation of a product or the rate of removal of a product

o The time taken for the concentration of one of…

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If you plot a concentration vs. time graph and then work out the half-life of the reaction then at a
constant temperature, the half-life of a first order reaction will be equal wherever it is measured on
the graph.

Second order reactions
A reaction is second order with respect to…

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The rate vs. concentration graph for a second
order reaction produces a curve.

Zero Order Reactions
A reaction that is zero order with respect to a reactant is unaffected by concentration. In a zero order
reaction, the concentration term for the reactant is raised to the power of zero.


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Using experiments 1 and 2, a halving of [HCl] produces almost exactly a halving of the rate, so the
reaction is first order with respect to the acid catalyst [H+]. Using reactions 1 and 3, a halving of
[propanone] produces approximately a halving of the rate. The reaction is first…

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The shaded areas show the
proportions of particles having at least the activation energy at 2 different temperatures. So at
higher temperatures, there are more molecules with enough energy to react when they collide, so
the rate of reaction is higher.

Rate Determining Steps and Multi-Step Reactions
Most reactions do…

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This led to the suggestion of a one stage reaction in which both reactants are involved in
a single rate determining step:

In this substitution reaction, the nucleophile is the hydroxide ion. Chemists label this
mechanism SN2 ­ the two shows that there two species involved in the rate-determining

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How Far


Reversibility and Equilibrium
In general, for a reversible reaction at equilibrium:

This is the form for the equilibrium constant KC, where the concentrations of the reactants
and products are measured in moldm-3. [A], [B] are the equilibrium concentrations.
Equilibrium constants are constant at a fixed temperature.


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Make sure that the KC expression always relates the balanced chemical equation.

Equilibrium constants and the direction of change
If the value of KC is large then the position of equilibrium lies to the right.
On the other hand if KC is small then the position of equilibrium lies to…

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Acids, Bases and Buffers

Brønsted-Lowry Acids and Bases
An acid is a proton donor
A base is a proton acceptor

Acid Metal/Ammonium Name/Formula of Salt Comment/Explanation
Ion formed
H2SO Mg2+ Magnesium sulphate, Both H+ ions in the acid are replaced. Salts
4 MgSO4 of sulphuric acids are sulphates
H2SO Na+…


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