Rates of Reaction Flashcards
what is needed for a reaction to occur?
- particles must collide with sufficient energy which overcomes the activation energy.
- particles must collide with the correct collision geometry.
activation energy definition
the minimum kinetic energy required for a reaction to occur.
activated complex definition
an unstable arrangement of atoms. It is an intermediate between reactants and products.
what is an enzyme
a biological catalyst
homogeneous catalyst
a catalyst in the same physical state as the reactants
heterogeneous catalyst
a catalyst in a different physical state from the reactants.
how does using a catalyst increase the rate of reaction?
it provides an alternative reaction pathway with a lower activation energy.
negative effect if a reaction is too slow
it will not be economically viable
negative effect if a reaction is too fast
there will be a risk of explosion
average rate of reaction equation
average rate = change in q/change in t
relative rate equation
relative rate = 1/t units s^-1
do reactants with energy greater than that activation energy always collide?
no, they also need the correct collision geometry.
what happens to catalysts at the end of a reaction?
they are regenerated and therefore can be used again.
temperature definition
a measure of the average kinetic energy of all the particles in a sample.
effect of increasing temperature
the number of particles with Ek above Ea increases
when drawing graph: Ea stays the same, area under graph stays the same so draw to the right and slightly lower down
potential energy diagram purpose
shows the progress of a reaction from reactants to products
decreasing particle size
decreasing particle size increases surface area of the reactant.
more particles exposed results in greater chance of successful collisions, therefore increased rate of reaction.
increasing concentration
increases the number of particles. more particles result in greater chance of successful collisions, therefore increased rate of reaction
increasing temperature
increase speed of particles
particles moving at a greater speed result in more successful collisions, therefore increased rate of reaction.
more particles have energy greater than or equal to the activation energy.
increasing pressure
reactant particles are pushed closer together (same number of particles in a smaller volume). Therefore, more chance of successful collisions and increased rate of reaction.
when is relative rate calculation used
when it is difficult to measure the change in a chemical reaction (colour change etc)
enthalpy change equation
Hp-Hr
enthalpy change for exothermic reactions
negative
enthalpy change for endothermic reactions
positive