equilibrium and rxn rates Flashcards
law of mass action/ equillibrium expression
Keq= [C]^c [D]^d/ {A]^a [B]^b
- if a system is in equilibrium, than this ratio is constant
rate is always expressed as
units of concentration over time
M/L
whats the first thing I should think of when a question askes to determine the rate law for a reaction
what is rate law–> for nearly all irreversible rxn, the rate is proportional to the concentrations of the reactants raised to some experimentally raised exponent (THIS IS NOT THE SAME AS EQUILIBRIUM expressions)
difference between rate law and equillibrium expressions (or law of mass)
rate law= determined experimentally, equilibrium - raised to coefficients
rate law= only the concentration of reactants, equillibrium= both products and reactants
rate law= how quickly system will reach equilibrium
equilibrium constant= indicates where the equilibrium position lies
rate law
= k [A]^x[B]^y
what are x and y
the orders of the rxn
how can x and y be used?
x is the order with respect to A and y is with respect to B, and the sume of them is the order of the overall rxn
when is the only time you can assume that the orders and the stiociometric coefficients are the same?
the complete rxn mech is given, and the rate limiting step is indicated, then the coeffiecents on the reactants side are equal to the orders. !but doesnt work if rate-limiting leads to intermediate!
how to Keq and rate laws relate
Keq is equal to the ratio of the rate constant k of the forward rxn divided by the rate constant k-1 of the reversie reaction
when is rxn rate normally measured
at or near the beginning
how is k found
using chart - it is determined experiementally and is constant for a given rxn at given temp
zero- order rxn
rate of formation of C is INDEPENDENT of changes of concentration of A or B - only depends on temp or addition of catalyst
rate= k
first order rxn
directly proportional to only one reactant
second order rxn
either concentration of 2 reactants or the square of one
broken order rxn
non-interger orders
