Rates Flashcards
Rate of reaction
Change in concentration per unit time.
Activation energy
Minimum amount of energy needed to start a reaction
Why does higher temperature increases the rate of reaction ?
At higher temperature, there are more particles with E>Ea. There is a greater frequency of successful collisions.
Why does higher pressure/concentration increases the rate of reaction?
There are more particles per unit volume therefore greater frequency of successful collisons.
Why does breaking solid into smaller pieces increases the rate?
increases surface area therefore greater frequency of successful collisons.
Why the rate of reaction starts off fast and then slows down before the reaction stops?
Initially, there is a higher concentration of reactants so large frequency of successful collison.
As reactants start to get used up successful colisions become less frequent
Once more and more reactants are used up there can be zero successful collisons
Order 0 of reaction
Doesn’t affect the rate
order 1
As concentration is doubled, rate is doubled
Order 2
concentration is doubled, rate is 2^2
Using a large excess of a reactant
will mean the order of reaction is zero with respect to that reactant as the reactants concentration is effectively constant.
To carry out an iodine clock initial rates practical
Measure the fixed volume of reactants using measuring cylinder
Start the clock time until black colour appears
Record the time taken R=1/t
Change concentration of I- and keep total volume constant as the concentration is proportional to volume.
Arrhenius Equation
k=Ae^-Ea/Rt
Arrhenius Equation
lnk=lnA-Ea/Rt
The specie that take part in the rate determining step
the species determining step must match the specie in rate equation
catalyst
A substance which increases the rate of reaction without being used up.
