C11 Chemical kinetics Flashcards
what are rate laws?
mathematical expressions which relate the rate of the reaction to the concentration of reactants
for the following reaction, write a formula for the rate of loss of reactant A
aA + bB –> cC + dD
rate of loss of reactant A =
k x [A]^a x [B]^b
describe zero-order reactions and their rate equations
- simplest type of rate equations
- rate of disappearance of a reagent is constant and doesn’t depend on its concentration
how do you work out whether a reaction has zero order kinetics from experimental data?
- plot conc (y) against time (x)
- if this forms a straight line, your reaction is zero order
- gradient = -k
describe what is meant by a first order reaction
the rate of disappearance of a reagent is proportional to the amount of material remaining
for the first order reaction shown below, what is the equation that shows rate of loss of reactant A?
A –>P
k[A]
plotting [A] against time for a first order reaction gives an exponential curve. how do we plot a linear graph for first order reactions?
- plot the natural log of [A] against time
- gives a linear graph for first order reactions
what is half-life?
the time taken for half the concentration of reactant to decompose
what is the overall reaction order?
- the sum of the orders with respect to each reactant
- eg. 2 reactants both first order means the overall order would be second
explain the relationship between temperature and rate
- reactions tend to get faster as temperature increases
- as temperature increases, more molecules have sufficient energy to overcome the activation energy barrier
what 2 things must happen for 2 molecules to react?
- collision
- collide with sufficient energy to overcome Ea
what is collision rate linearly dependent on? what is exponentially dependent on temperature?
- linearly dependent on temperature
- fraction of molecules having sufficient energy to overcome Ea is exponentially dependent on temperature
after manipulating the Arrhenius equation to get a linear graph, what formula can we get for the gradient?
-Ea / R
what does ΔG equal when a reaction is at equilibrium?
0
what is the Arrhenius equation? what does it show?
k=Ae^(-Ea/RT)
shows the effect that temperature has on rate
integrated rate law for zero order reaction
[A] = -kt + [A]₀
integrated rate law for first order reaction
[A]t = [A]₀ e ^ -kt
what shape is the integrated form of the differential equation for zero order reactions?
linear
what shape is the integrated form of the differential equation for first order reactions? how can we change its shape?
exponential, must use logs to make it linear
