rates + equilibrium Flashcards
order of reaction definition
shows the extent to which the concentration of a reagent affects the rate of reaction
the power to which the concentration of a reagent is raised to in the rate equation
what does it mean if a reagent is 0 order
the rate is unaffected by changes in concentration of that reagent
what does it mean if a reagent is 1st order
if the concentration changes, the rate will change by the same factor/amount
what does it mean if a reagent is 2nd order
if the concentration changes, the rate will change by the square of that amount
rate constant k definition
the constant of proportionality in the rate equation
what affects rate constant k
temperature and catalysts, not concentration or pressure
how does temperature affect k
increase in temperature increases k value
- high temp = more kinetic energy = more successful collisions = high rate = larger k value
how do catalysts affect k
catalysts increase k
- catalyst = faster rate = larger k value
what does a very high k value mean
fast reaction rate
what does a very small k value mean
slow reaction rate
what is the overall order of a reaction
the sum of all orders of reagents taking part in reaction
half life definition
how long it takes for reactant concentration to half
what can be found from concentration-time graphs of a reaction
the order of the reactant can be found by measuring the half life
- if half life gets smaller = 0 order
- if half life stays constant = 1st order
- if half life increases = 2nd order
which step of a reaction is the rate determining step
the slowest step, as a reaction can only go as fast as the slowest part of a reaction
if the gradient of a first order rate-conc graph is measured what does this give
the value of k
this is because rate = k[reactant] so as conc = x axis and rate = y axis gradient = k
when determining composition of a reaction mixture, why is the analysis of a physical property preferable to a chemical analysis
- measuring the change in a physical property will not interfere with reaction
- chemical analysis means the reaction must be stopped so analysis can take place to determine composition
suggest 2 physical properties that could be measured + how
colour change of gases or solutions
- this could be done using a colorimeter calibrated with known concentrations of the coloured substance
release of gas
- this could be done with a gas syringe or by measuring loss of mass
what is the rate equation
rate = k[reactants]^order
what is the half life equation
k = ln(2) / half life
half life known as t 1/2
what is the arrhenius equation
k = Ae^(- Ea / R T)
rearranged to
lnk = -Ea / R T + lnA
what are all the variables in arrhenius equation
k = rate constant
A = pre exponential factor (aka arrhenius constant)
e = eulers constant
Ea = activation energy (Jmol-1)
T = temp (K)
R = gas constant
what 3 types of reactions does the arrhenius equation describe
- reactions involving gases
- reactions occurring in solution
- reactions occurring on the surface of a catalyst
mole fraction definition
the fraction of the total number of moles that each substance in a reaction is responsible for - the amount of moles of a component divided by total number of moles in the mixture
partial pressure definition
the proportion of the total pressure that each chemical in a reaction is responsible for - the amount of pressure that would be exerted by a gas within a mixture if it occupied the same volume on its own at the same temp
what types of substance can be included in kc and kp calculations
ones in gaseous or aqueous states
no solids or liquids!
partial pressure p(X) equation
p(X) = total pressure x mole fraction
homogenous equilibria definition
all species are in the same state
heterogenous equilibria definition
all species aren’t in the same state
what factors affect kc and kp
only temperature
concentration, pressure and catalysts have no effect
why does concentration/pressure not have an effect on kc and kp
changes in pressure or concentration change the position of the equilibrium, but as this affects concentration of reacting substances, the position of equilibrium moves back to minimise the effect of this change, overall no effect
why do catalysts have no effect on kc and kp
catalysts increase rates of forwards and backwards reactions equally so no effect
how does temperature affect kc and kp
for exothermic reactions, increasing temp = decreasing kc/kp as this favours the opposite reaction, so decreased products/increased reactants = decreased kc/kp
for endothermic reactions increasing temp = increasing kc/kp as this favour the forward reaction, so increased products/decreased reactants = increased kc/kp
