pm1b definitions Flashcards
half life?
equation?
for 1st order it is independent of what…
time taken to decrease the reactant conc by half.
equation: ln2/ t1/2
half life is independent of [A]
rate law
is an expression that relates reactant concentration to reaction rate
e.g. for the reaction A+B—> products
rate law is Rate=k [A][B]
rate constant, k
independent of.. but dependent on…
the larger the value of k…
The proportionality constant that connects the conc of the reactants to the rate of the reaction.
It is independent of concentration but dependant on temp.
The larger the value of k, the faster the rate of reaction.
initial rate
the rate at the start of the reaction, calculated by taking the gradient of the tangent at time=o
reaction order
Defines the relationship between rate and reactant concentration.
e.g. Rate=k[A], the rate is proportional to [A] therefore first order with respect to A.
For SECOND order reactions:
homomolecular reactions and rate law?
the integrated 2nd order rate law?
hetermolecular reactions and rate law?
Homomolecular- reaction involving two identical reactant molecules.
Rate= k [A]^2
integrated rate law:
1/[At] = kt +1/[A0]
Heteromolecular- reaction involving two different reactant molecules .
Rate=k[A][B]
Heteromolecular SECOND order extreme case 2:
Pseudo first order reaction kinetics
give an example in real life
Rate=k[A][B]
[B]0»_space;[A]0
[B] is in greater excess
SAY THIS FOR DEFINTION:A reaction that appears to follow first order kinetics with respects to ONE reactant even though it is in fact second order or higher.
Typically due to conc of one reactant being constant (the one in large excess) during the reaction whilst the other is being consumed (this is the one limiting the rate of reaction here it is [A]).
(One reactant is in large excess [B] and so comparatively its concentration doesn’t change over time, so the order is only really reliant on the concentration of the reactant NOT in excess [A].)
Commonly this is the case for reactions in water as the concentration of the water is unlikely to change over time.
activation energy
the minimum amount of energy needed for reactants to react to produce products and is a barrier to the reaction.
homogenous catalysis?
heterogenous catalysis?
Catalyst is in the same phase as the reactants, principally in solution.
Catalyst is in different phase, than that of the reactants, typically solid-gas, respectively.
auto catalysis reaction?
Where one of the reaction PRODUCTS acts as a catalyst for the same reaction or the coupled reaction. It increases the rate of the reaction.
elementary reaction?
how can rate law be determined from an elementary reaction?
Chemical species react directly to form products in a SINGLE reaction step and with a single transition state.
The rate law for an elementary reaction can be derived from the coefficients of the reactants in the balanced equation. For example, the rate law for the elementary reaction 2A + B → products, rate = k[A]²[B].
molecularity?
how to calculate molecularity?
Number of molecules of reactants involved in a chemical reaction.
Molecularity can be calculated by adding the coefficients of the reactants in an elementary. For example, the molecularity of the reaction 2A+B→C is 2+1=3
Rate determining step
The SLOWEST step of a chemical reaction and determines the speed (rate) at which the overall reaction proceeds
A chemical species that is formed in one elementary step and consumed in a subsequent step, and not in overall balanced equation.
