F325 Module 1: Summary

A summary of all the notes required for module one. Each specification point with relevant information regarding it.

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Chemistry Module one of Unit 2. A2 Level.
Module 1: Chemistry
>Measuring the Rate of Reaction from a CONCENTRATION-TIME graph
Rate of Reaction = Change in Concentration / Time for the change to take place
Find a tangent to the graph at the given point, and work out the gradient.
This is the rate of reaction at that time.
>Explain and use the terms `Order' and `Rate Constant'
The Order with respect to a reactant is the power to which the concentration of the reactant is raised
in the rate equation.
Rate = k[A]^x
X= Is the Order with respect to A
There are 3 orders we need to understand:
-Zero Order: Rate = k[A]^0 Anything to power of 0 = 1
The rate is Unaffected by changing the concentration of A
-First Order: Rate = k[B]1
This outlines that if [B] increase by 2 times, then the rate of reaction will increase by 2
times etc.
-Second Order: Rate = k[C]2
If [C] increases by 2 times, then the rate increases by 2^2 times. Similarly if [C] increased by
10 times then the rate would increase by 10^2 times.
The Rate Constant, K is the constant that links the rate of reaction with the concentrations of the
reactants raised to the powers of their orders in the rate equation.
Rate = K[B]^1[C]2
The Overall Order can be found by adding the powers of order together e.g. The above rate
equation has an overall order of: 1 + 2 = 3. Also you must remember that the rate equation can be
determined only from experimental results.
Units of Rate Constants:
The units can be worked out by making K the subject in the rate equation:
E.g. for first order Rate = K[A] therefore K = Rate / [A]
Units for K are therefore moldm-3 s-1 / moldm-3 which gives s-1
Always write the units from positive to negative e.g. A third order, Rate = K[A]^2[B]^1 therefore K =
moldm-3 s-1 / (moldm-3 x moldm-3) x (moldm-3)which gives: dm6mol-2 s-1.
By Ryan Janjuha 2012

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Chemistry Module one of Unit 2. A2 Level.
>Explain and use the terms Order & Half life
Order is explained previously, the Half Life of a reactant is the time taken for the concentration of
the reactant to reduce by half.
>Deduce the half life of a first ­order reaction from a concentration-time graph.
The first-order reaction can easily be identified from a concentration-time graph.
1. A first order reaction has a Constant Half Life.
2.…read more

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Chemistry Module one of Unit 2. A2 Level.
changes in concentration do example if concentration equivilant to the change2. For
not change the rate of reaction. doubled then the rate would example a change in
Rate = K[A]0 also double. concentration of 2 times,
Rate = K[B]1 would mean rate changes by 22
times.…read more

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Chemistry Module one of Unit 2. A2 Level.
>Propose a rate equation that is consistent with the rate-determining step
>Propose the steps in a reaction mechanism from the rate equation and the balanced equation
for the overall reaction
Firstly it is important to understand what is meant by the `Rate determining step', put simply it is: the
slowest step in the reaction mechanism of a multi-step reaction.…read more

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Chemistry Module one of Unit 2. A2 Level.
2NO + 02 2NO2
RDS ­ is the slowest step in a reaction mechanism of a multi-step reaction
There are two molecules of NO in the rate equation. Possible mechanism outlined below.
NO + NO N2O2
N2O2 + O2 2NO2
>Deduce expressions for the equilibrium constant, Kc, for homogeneous reactions
The equilibrium law tells us the relative proportions of reactants and products present at EQ.…read more

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Chemistry Module one of Unit 2. A2 Level.
>Calculate the concentration of quantities of substances present at Equilibrium.
This method is best explained when referring to page 129 in the OCR textbook. The method for
working out the concentration of quantities of substances present at EQ, is the following:
1) Assuming you are given data such as: an overall dynamic EQ reaction equation, and data on
some of the reactants, maybe in mol or the concentration of them.…read more

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Chemistry Module one of Unit 2. A2 Level.
>State that Kc is unaffected by changes in concentration, pressure and the presence of a
catalyst.
Although Kc is altered by temperature, its value does not change by changes in concentration &
pressure. Catalysts affect the rate of a reaction, but not the position of equilibrium. Catalysts speed
up both the forward and reverse reactions in the equilibrium by the same factor, we reach
equilibrium quicker but the position is unchanged by the action of a catalyst.…read more

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Chemistry Module one of Unit 2. A2 Level.
>Understand that compromise conditions rely on a balance between Kc and K
To summarise the sections regarding k and Kc so far, we understand that:
K Kc
K is the rate constant, measures the rate of Kc is the equilibrium constant, and compares the
reaction. relative concentrations of reactants and
A large value of K means a fast rate of products present at EQ.
reaction.…read more

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Chemistry Module one of Unit 2. A2 Level.
>Describe an acid as a proton donor and a base as a proton acceptor.
A Bronsted-Lowry ACID is a proton H+ donor.
A Bronsted-lowry BASE is a proton, H+ acceptor
An Alkali is a base that is soluble in water forming OH- ions.
>Illustrate the role of H+ in the reactions of acids with carbonates, bases, alkalis and metals
When an acid is added to water it dissociates releasing H+ ions into solution.…read more

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Chemistry Module one of Unit 2. A2 Level.
A molecule of an acid must contain hydrogen that can be released as H+. It is important to realise that
although an acid is called a proton donor, it does not just happen on its own. There must always be a
base present in order to accept it.
An acid-base pair is a set of two species that tranform into each other by gain or loss of a proton.…read more

Comments

dan

these notes are fantastic, you dont happen to have the other 2 modules do u? i love the way u follow the spec. :)

Beccy_Wright3107

Last page was very useful :)

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