Unit 4 Approxmation Rule Walkthrough
Initially 4.00 mol of carbon monoxide and 3.00 mol of bromine gas are placed into a 2.5 L container, what is the concentration of the reactants and Carbonyl bromide at equilibrium?
Keq = 4.5x10-5
1. Find chemical equation
2. Balance chemical equation
3. Make ICE table
4. Fill in ICE table
5. Is this question an approximation rule (more than 1000x difference)?
6. Write keq equation with products and reactants
7. Cross out x for reactants because we can assume that the initial concentration of the reactants will be very similar to the concentration at equilibrium
8. Solve for x
9. Use x to solve for each chemical’s equilibrium concentration
CO(g) + Br2(g) ⇌ COBr2(g)
1CO(g) + 1Br2(g) ⇌ 1COBr2(g)
| CO(g) | Br2(g) | COBr2(g) | |
| I | |||
| C | |||
| E |
| CO(g) | Br2(g) | COBr2(g) | |
| I | 1.60 mol/L | 1.20 mol/L | 0 |
| C | -x | -x | +x |
| E | 1.60 -x | 1.20 -x | x |
1.6 / 4.5x10-5 = 35555.555... ∴ Yes it is more than 1000x difference
Keq = [Products] / [Reactants]
Keq = [COBr2(g)]1 / [CO(g)]1[Br2(g)]1
4.5x10-5 = [x]1 / [1.60 -x]1[1.20 -x]1
4.5x10-5 = x / (1.60)(1.20)
4.5x10-5 = x / 1.92
(4.5x10-5)(1.92) = x
x = 8.64x10-5
[COBr2(g)] = x
[COBr2(g)] = 8.64x10-5 mol/L
[Br2(g) ] = 1.20 - x
[Br2(g) ] = 1.20 -8.64x10-5
[Br2(g) ] = 1.19991 mol/L
[Br2(g) ] = 1.20 mol/L
[CO(g) ] = 1.60 - x
[CO(g) ] = 1.60 -8.64x10-5
[CO(g) ] = 1.59991 mol/L
[CO(g) ] = 1.60 mol/L