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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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This means that doubling the concentration of a reactant doubles the rate of reaction. Rate is
proportional to [reactant]. This means a plot of rate vs. concentration produces a straight line
through the origin.
If you plot a concentration vs. time graph and then work out the half-life of the…

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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
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
H2SO4 Mg2+ Magnesium sulphate, Both H+ ions in the acid are replaced.
MgSO4 Salts of sulphuric acids are sulphates
H2SO4 Na+ Sodium…

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A strong acid is one which dissociates fully in solution
A weak acid is one which only partially dissociates in solution

pH scales

( )
Ionic Product of Water
There are H+ and OH- ions in pure water because of the transfer of hydrogen ions
between water molecules.

Or more…


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