Reaction Rate Vs Equilibrium Constant, Coefficients, and the lke

[somuchwater]

Hi,
Here's my source of confusion.

So we use law of mass action and use coefficients of a reaction to determine the exponents of a reaction. aka.

1 A + 2 B => 3 C + 4 D

==>

[C]^3 * [D]^4
--------------------- = K
[A]^1 * ^2

So how exactly does this mesh with determining if a reaction is first order, zero order, etc.?

Like if my exponents above were

[C]^3 * [D]^4
--------------------- = K
[A]^1 * ^1

then isn't the reaction 2nd order?

If we already have the exponents what is the point of a running a reaction law experiment?

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[erythrocyte666]

reaction order and equilibrium constant are COMPLETELY separate, not related to one another at all
while eq. constant is derived from reaction stoichiometry, reaction order can only be determined via experiments

 

[somuchwater]

Aren't they related for an elementary reaction?

 

[Eaglefan]

for an elementary reaction, yes they would correlate but you should still think of them as separate (just go by exponents, don't think about Keq)

aA+bB-->cC K= [C]^c / ([A]^a*^b) rate= k[A]^a*^b

for a non-elementary rxn with the same formula, K is the same but the rate law would be different