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CHEM4

Chapter 1.1 rate of chemical reactions

Rate of reaction is the change in concentration with unit time

To find the rate of reaction at an
instant, plot a graph with
concentration and time
and place a tangent at the curve and
find the gradient.









1.2 rate expression and order…

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1.3 Determining the rate equation


To determine the order of each species in an equation plot a graph of concentration with
rate.





Small changes in temperature produces large changes
in reaction rates due to kinetic energy and activation energies.


1.4 Ratedetermining step


In a multistep reaction the rate determining step…

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2.2 Calculations using equilibrium constant expressions

Equation CH3OH CHOOH CHOOCH3 H2O
At start 1 mol 1 mol 0 mol 0 mol
At equilbrium (1x) mol (1x) mol x mol x mol

Kc = 4.0
Suppose at equilibrium the volume is Vdm3. (YOU WILL NOT NEED TO USE
VOLUME IF THE…

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Doing the same to work out concentration of a reactant:


Equation CH3COCH3 HCN CH3C(CN)(OH)CH3
At start 4.00 mol X mol 0 mol
At equilbrium (4.00 1.00) (X 1) mol 1.00 mol
3.00 mol (X 1) mol

Volume of 2.00 dm3
Kc = 30.0 mol1dm3

CH3COCH3 = 3.00 / 2.00

HCN…

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[Reactants] concentration of products and reactants etc....






3.1 Defining an acid

The BronstedLowry description of acidity uses protons

An acid is a substance that can donate a proton (H+)
A base is a substance that can accept a proton

H2SO4 + HNO3 H2NO3+ + HSO4
Acid base


Water acting as…

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1.0 x 1014 = [H+]2

1.0 x 107 = [H+] or [OH]






3.2 The pH scale


pH = ­log10[H+]

­pH
from pH to H+ you have to do 10



Finding OH from pH

Say pH is 10
This means 1.0 x 1010 = [H+] we already know [H+] x [OH]…

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3.3 Finding pH of weak acids and bases


A weak acid equilibrium can be written as HA H+ + A

Put it into a constant: Kc = [H+] [A] but for an acid the symbol Kc is turned into Ka
[HA]

The larger the value of Ka the further the…

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3.4 Acidbase titrations


In a titration the equivalence point
indicated by the red line is where the
acid or alkali has just been
neutralised. However the point is not
always at pH 7.




You need to know CV/1000 = N













3.5 Choice of indicators for titrations

The choice for an…

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litmus 6.5 5 - 8

methyl orange 3.7 3.1 - 4.4
phenolphthalein 9.3 8.3 - 10.0

The halfneutralisation point

Half way between zero and the equivalence point is the halfneutralisation point.
We know there is little change to the pH when we add acid (or a base) to the titration.…

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The function of having a salt component of a buffer is to act as a source of A ions to remove
any additional H+ ions.

Such as:

Na+A Na+ + A

The point of a buffer is to maintain the concentration of H+ ions and so pH. The [HA] and…

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