Equilibrium Law in chemical reactions
...a lot like rate law equations!
*as we’ve discussed, in a closed system, a reaction does not go to
completion!*
The equilibrium constant, K (capital K that is !)
- when: aA + bB
cC + dD
K=
- A, B, C and D are chemical entities in gas or aqueous phases. And a, b,
c, and d are the coefficients in the balanced equation.
- The concentrations are the MOLAR concentrations at equilibrium
-The molar concentrations of the products are always in the numerator.
and the reactants are in the demoninator.
-No matter what the concentration of the reactants are, the value of K
will always remain constant.
-is used for gaseous and aqueous equilibria
Equilibrium constant and reaction kinetics
-remember that the rate of the forward reaction equals the rate of
the reverse reaction:
For the forward reaction:
For the reverse reaction:
At equilbrium:
Writing equilibrium Law expressions for equlibrium reactions:
Example #1: Write the equilibrium law expression for the reaction in
which nitrogen gas reacts with hydrogen gas in a closed system to
produce gaseous ammonia.
1. Write chemical equation for equilibrium reaction
2. Write equilibrium law equation
Example #2: Write an equilibrium law equation for the reaction where
nitrogen monoxide reacts with oxygen to form nitrogen dioxide at
SATP.
Calculating K
Example #1: Nitrogen and hydrogen combine to form ammonia (see
example 1 on most recent page). Calculate the value of the equilibrium
constant for this reaction if the following concentrations were
measured at equilibrium at 500C.
1. write equilibrium law equation
2. sub in equilibrium concentrations and solve for K.