OCR A2 Unit 2 Equilibria, Energetics and Elements (F325)

Revision notes for Unit 2

HideShow resource information
  • Created by: Anisa
  • Created on: 25-05-13 16:32
Preview of OCR A2 Unit 2 Equilibria, Energetics and Elements (F325)

First 334 words of the document:

There are many different ways of following the rate:
Gas volume ­ if a gas is given off, you could collect in a gas syringe and record how much you
get at regular time intervals.
Colour change ­ you can track the colour change of a reaction using a colorimeter.
Electrical conductivity ­ if the number of ions changes, so will electrical conductivity.
Initial rate of reaction ­ the rate at the start of the reaction (y/x)
Clock Reactions ­ measures the time from the start of the reaction until visual change i.e.
precipitate, disappearance of solid or colour change. The shorter the time, the faster the initial rate
(Usually colour change)
The rate equation is a way of calculating the rate of a chemical reaction. The rate equation has a
general form of: A+B Products, rate= k[A] [B] , where A and B are the reactants, k is a constant
called the rate constant. k relates the rate of a chemical reaction with the reactant concentrations ­
the bigger it is, the faster the reaction. m is order of the reaction with respect to A; n is order of
reaction with respect to B.
Rate ­ mol dm³ s [A] & [B] ­ mol dm³
Temperature change affect rate constant ­ reactions happen when the reactant particles collide
and have enough to break the existing bonds. Increasing the temp speeds up the reactant particles,
so that they collide more often. It also increases the chances of the particles reacting when they do
hit each other, as they have more energy. Therefore increasing temp, increases rate of reaction.
According to rate equation, reaction rate depends only on the rate constant and reactant
concentrations. A higher temperature increases the rate of reaction and the reaction will have a
higher rate constant.
Concentration/Time graphs AND Rate/Concentration graphs

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

The rate is proportional to the
Changing the concentration proportional to the concentration
[concentration]² ORDER 2
doesn't change the rate ORDER ORDER 1
0 Half-life increases
Half-life stays the same ­
Half-life decreases independent of the concentration.
The effect of a temperature change on k
When the temp of a reaction is increased the molecules move faster, so there are more collisions and
more chance of product being formed.…read more

Page 3

Preview of page 3

Here's a taster:

Dynamic Equilibrium ­ rate of the forward and reverse reactions are equal and concentrations of
reactants and products are constant.
Kc is an equilibrium constant, measured using concentrations ­ NOT SOLIDS!! The only factor that
affects Kc is temperature, NOT pressure, concentration or catalysts!
Exothermic reaction Endothermic reaction
Temperature raised Kc decreases Kc increases
Temperature reduced Kc increases Kc decreases
Increase in temperature, shifts the position of equilibrium in endothermic direction.
Decrease in temperature shifts the position of equilibrium in exothermic direction.…read more

Page 4

Preview of page 4

Here's a taster:

Weak acids
Weak acids are poor proton donors and are only partially dissociated in aqueous solution.
Therefore the dissociation isn't 100% and [H+] can't be calculated directly from
concentration of acid.
Ka shows the extent of acid dissociation.
Equilibrium constant for this reaction is HA(aq) H+(aq) + A-(aq)
Kw = [H+] [OH-] = 1.00 x 10^-14 mol^2dm^-6
Indicators and acid-base titration
Indicators are either weak acids or weak bases.…read more

Page 5

Preview of page 5

Here's a taster:

A buffer solution is one that minimises pH changes on addition of small amounts of acid and base.
Buffers are important solutions especially in biological systems.…read more

Page 6

Preview of page 6

Here's a taster:

D-block elements that have an ion with an incomplete d sub shell are transition elements.…read more

Page 7

Preview of page 7

Here's a taster:

A ligand must have at least 1 lone pair of electrons; otherwise it won't be able to form a coordinate
bond. Ligands with 1 pair ­ monodentate. Ligands with 2 lone pairs - bidentate (en). Ligands with
more than 2 lone pairs ­ multidentate.
All Complex ions can have Stereoisomers, whether monodentate or multidentate; optical isomers
(non-superimposable mirror images of each other) and Cis/trans isomerism.…read more

Page 8

Preview of page 8

Here's a taster:

LE (more exothermic), the stronger the bonding.
Ionic charge ­ higher the charge on the ions, more energy is released when an ion lattice forms and
the LE will be more negative (more exothermic).
Ionic size ­ smaller the ionic radii of the ions, more negative (more exothermic) the LE. Small ions
attract more strongly because of their high charge density.…read more

Page 9

Preview of page 9

Here's a taster:

If G is ­ve then it is a feasible reaction. If it's a +ve value, it's not feasible. * Even if it is ­ve, the
reaction might have high activation energy and therefore not work.
Some endothermic reactions can happen spontaneously, if the entropy is high enough the reaction
will happen itself.…read more

Page 10

Preview of page 10

Here's a taster:

Reaction might be so slow that you can't even see it happening
Storage and fuel cells
Modern energy storage cells work just like electrochemical cells. A fuel cell uses the energy from a
reaction of a fuel with an oxidant ­ usually oxygen ­ to create a voltage.
Hydrogen-oxygen fuel cell
A fuel cell uses energy from the reaction of a fuel with oxygen to create a voltage. Recatants flow in
and products flow out while the electrolyte remains in the cell.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »