Calculating Equilibrium Constant
Rucete ✏ Chemistry In a Nutshell
Example how to calculate
P. A mixture of 5.0 mol of H2 and 10.0 mol of I2 is placed in a container of 5 liters at 450 ° C, allowing the equilibrium to be reached. The [HI] at equilibrium is 1.87 mol L-1. Calculate the reaction with Kc.
- Use the equation to determine the mole ratio.
1mol H2 + 1mol I2 → 2mol HI
- Make sure that all initial concentrations are expressed in mol L^-1.
Volume = 5L, [H2] = 1 mol L^-1; [I2] = 2mol L^-1
- Find the amounts of each reactant used.
H2 used = [HI] x mole ratio H2 / HI
= 1.87 x 0.5
= 0.935mol L^-1
I2 used = 1.87 x 0.5
= 0.935mol L^-1
- Find the amount of each of the reactants present at the equilibrium
H2 present = initial concentration – amount used
= 1 – 0.935
= 0.065 mol L^-1
I2 present = 2 – 0.935
=1.065 mol L^-1
- Write out the final concentration at equilibrium and substitute the values in the equilibrium expression to find Kc.
[H2] = 0.065mol L^-1; [I2] = 1.065mol L^-1; [HI] = 1.87
Kc = [HI]^2 / [I2][H2]
= 1.87^2 / 0.065 x 1.065
= 50.51
Summary
Tags:
Chemistry in a nutshell