Question

write the keq for the following reactions:
1n₂(g) + 3 h₂(g) → 2 nh₃(g)
1h₂(g) + 1 br₂(g) → 2 hbr(g)
1caco₃(s) → 2 cao(s) + 1 co₂(g)
write the keq for the following reactions:
1n₂(g) + 3 h₂(g) → 2 nh₃(g)
where you have 1.5m of n2

Explanation:

Step1: Define Keq for gas reactions

For a reaction $aA_{(g)} + bB_{(g)}
ightarrow cC_{(g)} + dD_{(g)}$, $K_{eq} = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Solids are excluded.

Step2: Keq for first reaction

Substitute coefficients of $\ce{N2(g) + 3H2(g) -> 2NH3(g)}$
$K_{eq} = \frac{[\ce{NH3}]^2}{[\ce{N2}][\ce{H2}]^3}$

Step3: Keq for second reaction

Substitute coefficients of $\ce{H2(g) + Br2(g) -> 2HBr(g)}$
$K_{eq} = \frac{[\ce{HBr}]^2}{[\ce{H2}][\ce{Br2}]}$

Step4: Keq for third reaction

Exclude solids $\ce{CaCO3(s)}$ and $\ce{CaO(s)}$
$K_{eq} = [\ce{CO2}]$

Step5: Keq for repeated first reaction

Concentration of $\ce{N2}$ does not change the Keq expression
$K_{eq} = \frac{[\ce{NH3}]^2}{[\ce{N2}][\ce{H2}]^3}$ (with $[\ce{N2}]=1.5\ \text{M}$ when calculating value)

Answer:

1. $K_{eq} = \frac{[\ce{NH3}]^2}{[\ce{N2}][\ce{H2}]^3}$
2. $K_{eq} = \frac{[\ce{HBr}]^2}{[\ce{H2}][\ce{Br2}]}$
3. $K_{eq} = [\ce{CO2}]$
4. $K_{eq} = \frac{[\ce{NH3}]^2}{(1.5)[\ce{H2}]^3}$