define 0th order
rate is independent of concentration
reactants aren’t in rate equations because they don’t affect rate
how to find if a substance is first order from a graph
measure a constant half life
use formula ln2/t0.5
define first order
rate is proportional to concentration
appears in rate equation to the power of 1
how to identify first order substances from a graph
half life is constant
define second order
rate is proportional to concentration squared
how to check if a substance is second order from a graph
half life’s shouldn’t be constant
how to work out units for rate constant
mol dm-3 however many times on top and bottom
how to find concentration constant
plug in rate of reaction, K and the reactant concentrations to the powers they should be and
how to find average rate
measure average rate with different combinations o concentrations
how does an iodine clock work
the appearance of iodine as a product is delayed and using iodine as an indicator for the blue-black clear point
define mechanism of a reaction
series of steps
how are the orders related to the reaction mechanism
the rate determining step determines rate equation
what are the 3 rules for determining rate-determining step
1- 0th order reactants can only be involved in steps after the RDS
2- 1st order reactants are usually in RDS (rarely before)
3- 2nd order reactants either:
- 2x species in RDS
- one species in RDS = one before
- rarely 2x before
what is the extra rule for inventing mechanisms based on the rate equations
sum of steps = overall balanced equation
what does the arrhenius equation do
links rate constant, temperature and activation energy
what is the exponential version of Arrhenius equation
k=Ae^(-Ea/RT)
what is the linear version of Arrhenius equation
ln(k) = ln(A) + (-Ea/R)(1/T)
this can form y=mx+c to find from a linear graph
