1. Equilibrium Expressions
Nov 2017

2. The equilibrium reaction below was studied at 448oC: H2(g) I2(g)  2HI(g) Colourless Purple Colourless
The following observations were made:
The purple colour never completely disappears
The same intensity of purple is present at the end of the reaction regardless of whether the reaction starts with, for example, 1 mole each of H2 and I2 or it starts with 2 moles of HI.

3. The equilibrium reaction below was studied at 448oC: H2(g) I2(g)  2HI(g) Colourless Purple Colourless
The following relationship exists between the final concentrations of H2, I2, and HI regardless of starting concentrations:
[HI]2 = this value changes if T changes
[H2][I2]
49.5 is called the equilibrium constant Keq and the relationship is called the equilibrium expression.

4. The equilibrium reaction below was studied at 448oC: H2(g) I2(g)  2HI(g) Colourless Purple Colourless
The equilibrium expression can easily be derived for any equilibrium reaction – the products go in the numerator, the reactants in the denominator and the coefficients become the exponents. 2A(aq) + 3B(aq)  C(aq) Keq =

5. Write the equilibrium expressions for the following equilibrium reactions:
SO(g) + O2(g)  SO3(g)
2SO2(g) + O2(g)  2SO3(g)
N2(g) + 3H2(g)  2NH3(g)
C(s) + O2(g) CO2(g)
2Na(s) + Cl2(g)  2NaCl(s)