Br₂(g) ⇌ 2 Br･(g) Kp = 2.48 × 10⁻³ at 1650 °C. A 5.00 L vessel at 1650 °C is filled with Br₂(g) at an initial pressure of 5.00 atm equilibrium. Pressure (in atm) of Br･(g) at equilibrium?

Answer 1

Br₂(g) <==> 2Br^-(g)

Use an ICE table

Br₂(g) <==> 2Br^-(g)

5 atm............0 atm.........Initial

-x................+2x..............Change

5-x................2x..............Equilibrium

Write the equilibrium expression, and then fill in the known values and solve for x:

Kp = (P_Br-)² / (P_Br2)

2.48x10^-3 = (2x)² / 5-x (assume x is small relative to 5.00 and ignore it in the denominator)

2.4x10^-3 = (2x)² / 5

2.4x10^-3 = 4x² / 5

4x² = 0.012

x² = 3.0x10^-3

x = 0.0548 (this is only 1% of 5.00 so above assumption was valid and we avoided using the quadratic)

Pressure (in atm) of Br- @ equilibrium = 2x = (2)(0.0548) = 0.1096 atm = 0.110 atm (3 sig. figs.)