GCSE Chemistry Revision Notes: The effect of pressure on reaction rate (speed)
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3b. What is the effect
of changing pressure
on the rate of a reaction involving gaseous reactants?
chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE chemistry, O level
& ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old
science students for national examinations in chemistry -
Doc Brown's chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE chemistry, O level & ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry -Doc Brown's Chemistry KS4 science GCSE/IGCSE/O level Revision Notes - Factors affecting the Speed-Rates of Chemical Reactions
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3. Factors affecting the Rate of Chemical Reactions
REACTION RATE and GAS PRESSURE of REACTANTS
Varying the PRESSURE of a reactant gas
For each factor I've presented several particle diagrams to help you follow the text explaining how the particle collision theory accounts for your observations of reaction rate varying with the pressure of reactant gases (some 'work' better than others!)
Solid reactants and solutions are NOT affected by change in pressure, their concentration is unchanged, so no change in the rate of the reaction.
THEORETICAL INTERPRETATION of CHANGING THE PRESSURE of a REACTING GAS
Applying particle models
The first diagram gives an idea of how to think about the probability of fruitful collisions.
Pictures of a gaseous particles (molecules) undergoing changes in a gaseous chemical reaction
== increase pressure ==>
This illustrates a mixture of gases A and B colliding and potentially reacting
The greater the concentration (pressure) of the gas molecules, the greater the probability of collision
The product molecules are not shown, but just imagine how more collisions will occur in the right-hand diagram!
Pictures of a gaseous particles (molecules) undergoing chemical changes on the surface of a catalyst
== inc. P =>
This illustrates a gas reacting on the surface of a solid catalyst.
Again, the product molecules are not shown, but just imagine how more collisions will occur in the right-hand diagram on the catalyst surface.
As you increase the pressure, you effectively increase the concentration of the reactants and thereby increase the chance of a fruitful collision.
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