5.1.1 - How Far? Flashcards
define rate as an equation
change in concentration/ change in time
what are the units for rate
mol dm-3 s-1
what is an order of reaction
how changing the concentration of a species affects rate
zero order
rate ∝ [A]^0
(conc. A has no effect on rate)
first order
rate ∝ [A]
second order
rate ∝ [A]^2
how to calculate the overall order of a reaction
add up the orders of all the reactants in the equation
rate equation (general form)
rate = k[A]^m[B]^n
concentration time graph: zero order
straight line, negative gradient
gradient = k
concentration time graph: first order
decreasing gradient with a constant half life
gradient = rate (can be used to find k)
define half life (t1/2)
the time taken for concentration to half
concentration time graph:
equation for finding k, using the half life of a 1st order reaction
k = (ln2)/half life
concentration time graph: second order
steep decreasing gradient with no constant half life
examples of continuous monitoring methods
change in mass, gas volume, colorimetry
rate concentration graph: zero order
horizontal line, gradient = 0, rate = k
rate concentration graph: first order
straight line graph through origin
positive gradient, rate = k[A]
rate concentration graph: second order
exponential through origin
k = gradient of conc^2/rate graph
why are many reactions multi-step
collisions of many moles is very unlikely
if species have the same charge
define reaction mechanism
the series of steps that make up an overall reaction
define rate determining step
the slowest step in a multi-step reaction
about the rate determining step
- rate equation only includes species of RDS
- orders in rate equation match the number of species in the RDS
what factors mean increasing temperature increases k
- more particles exceed Ea
- kinetic energy of particles increases so frequency of collisions increases
why is increased Ea more significant than increased collisions
increases collisions is small in comparison to having more particles over Ea
arrhenius equation
k = Ae^(-Ea/RT)
logged arrhenius equation
lnK = (-Ea/R)*(1/T) + lnA
