AQA ( additional science)

First unit of chemistry in additional science AQA

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Additional
Science revision
booklet
By Rainu Kaur
Chemistry
Rates of reactions
The rate of a reaction measures the speed of a reaction.
As the reactions takes place the mass will decrease, if a gas is given off we can measure
the rate of reaction by collecting the gas and measuring its volume at timed intervals. We
can use a balance that is attached to a computer to monitor the mass continuously.
Another method is to measure the time taken for a certain amount of solid to appear in a
solution. A reaction stops when one of the reactants is used up.
FAST REACTIONS: EXPLOSIONS
SLOW REACTIONS: RUSTING
Other ways to measure rates of reaction:
Colour changes
Formation of precipitate
PH changes
Temperature changes
Time taken for a given mass to react
Rate = amount of product formed
Time
Or
Rate = amount of reactant used up
Time
1

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Factor Reactions affected Change made in Effect on rate of
condition reaction
CATALYST Slow reactions that Reduces the amount of Increases rate of
can be speeded up energy required for reaction so that
by adding a suitable reaction to take place more collisions can
catalyst (activation energy) happen.…read more

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If the concentration of a solution is increased there are more particles dissolved in
the same volume. This means the dissolved particles are closer together and so they
collide more often.
Double concentration of acid
Double number of particles
Double chance of collisions
Double the rate of reaction
Effect of temperature
Increasing the temperature increases the speed of the particles in a reaction mixture.
This means they collide more often which increases the rate of reaction.…read more

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A+B C + D
Two arrows are used to show the reaction is both forward and reverse
When there is no change in the amount of products and reactants (forward
and reverse at the same rate) EQUILIBRIUM is reached.
Example: Hydrochloric acid + Ammonia Ammonium Chloride
Double arrows means its reversible
Single arrows is not reversible
The rate of the forward and reverse reaction at equilibrium stays the same.
We can change the yield of the reaction by changing the temperature of the reaction.…read more

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The conditions which give the best profits for the manufacturers mean a
compromise for the conditions. Temperature gives a faster rate but reduces yield.
Pressure gives a faster rate and yield but is expensive.
TEMPERATURE 450 c = FASTER RATE, LOWER YIELD
PRESSURE 220 atm = FASTER RATE, GREATER YIELD, COSTLY
IRON CATALYST = FASTER RATE, LOWERS ACTIVATION ENERGY
They use pressures of about 200-350 atm to increase produce but it is expensive to
build chemical plants that operate at high pressures.…read more

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COVALENT bond to make a bromine molecule Br . In electrolysis REDUCTION
and OXIDATION happen we call it REDOX.
At the cathode: Pb + 2e Pb
At the anode: 2Br Br + 2e
Electrolysis of Brine
Brine is a solution of sodium chloride in water. The electrolysis of BRINE is an
enormously important INDUSTRIAL PROCESS. When we pass an electric current
through Brine, we get three products.…read more

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ACID + METAL SALT + HYDROGEN
E.g. Hydrochloric acid + Magnesium Magnesium chloride + Hydrogen
Neutralisation
OH + H H 0
ACID + ALKALI SALT + WATER
E.g.…read more

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Electrical Power = voltage ÷ Current
Mains electricity
Blue goes left, brown goes right and striped goes to the top.
The mains electricity supply is 230V.
When you plug in something with a metal case into a wall socket you automatically
`EARTH' the metal case which means it is connected electrically to the ground. This
stops the metal case becoming `LIVE' it is becomes live and the wire breaks you can
become electrocuted.…read more

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You will get an electric shock if the live wires touch the metal case (the outer
layer)
The Fuse
The fuse breaks the circuit if the current is too high.
The fuse melts easily then breaks the circuit
Fuses have common ratings; most common are 3A, 5A, 10A, 13A
Fuse should be rated slightly higher than the current the device needs.
A circuit breaker can be used in place of a fuse.…read more

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