chemical kinetics 1 Flashcards
what is the rate of reaction
change in concentration over the change in time
what two things are necessary for a reaction to occur
particles must collide with the correct orientation
particles must meet the activation energy
what 5 factors affect rate of reaction
concentration/pressure
pH
surface area
temperature
catalyst
what is the correct orientation of particle collision
delta + should be facing delta -
define activation energy
minimum investment of energy that must be supplied to enable bonds in reactants to stretch and break as new bonds are formed
why does increasing the concentration increase the rate of reaction
more molecules per unit volume so a greater chance of collision - more collisions per unit time
effect of increased surface area on rate
more collisions per unit time
effect of increasing temperature on rate of reaction
increases the kinetic energy of the molecules
results in more frequent collisions and collisions have higher energies
more successful collisions per unit time
effect of pressure on rate of reaction
more molecules per dm3
greater chance of collisions
more collisions per unit time
what doe the Maxwell Boltzmann diagram show
number of molecules having particular kinetic energies at a constant temperature
what does an increase in temperature do to the peak on a Maxwell Boltzmann diagram
moves to the right
there are more molecules with the activation energy
area under the curve must remain constant
define a catalyst
a substance that speeds up the rate of reaction by providing an alternative route or mechanism with a lower activation energy
effect of catalyst on rate of reaction
catalysts lower the activation energy
more particles have reached the activation energy
more successful collisions per unit time
method for measuring changes in a volume of gas
1 use a gas syringe and record volumes at frequent intervals
2 plot volume vs time graph
3 tangent to the steepest part to find initial rate
4 repeat with other concentrations
method for measuring colour change (colorimetry)
1 choose filter of complimentary colour and calibrate colorimeter against water
2 mix reagents
3 record absorbance of transmission at frequent time intervals
4 region of most rapid change = initial rate
5 repeat with other concentrations
what is a first order rate concentration graph
upwards straight diagonal
what is a second order rate concentration graph
upwards curve
what is a first order concentration time graph
downwards straight diagonal
what is a second order concentration time graph
downwards curve
what is a zero order rate concentration graph
parallel to x axis
what is a zero order concentration time graph
downwards straight diagonal
example of a rate equation
rate = k[A]m[B]n
where m and n are the order of reaction with respect to each chemical
what is k
the overall rate constant
what is the overall order of the reaction
sum of the orders of the concentrations of the reactants
define half life of a chemical reaction
the time taken for the concentration of a component to decrease to half its initial value
which order of reaction has a constant half life
first order
which order is it if half lives become longer (not constant)
an order greater than first
define rate constant
relates to the rate of a chemical reaction at a given temperature to the product of the concentrations of reactants
define order of reaction
the power to which the concentration of that reactant is raised in the rate equation
explain in terms of collision and energy, why lowering the temperature decreases the rate of reaction (2 marks)
particles have less kinetic energy
less particles meet the activation energy
less successful collisions per unit time
state how a catalyst increases the rate of a chemical reaction (1 mark)
decreases the activation energy
more particles are able to react under the same conditions
