Answer:
Kc = 0.791
Explanation:
Step 1: Data given
Hydrocyanic acid = HCN
ammonia = NH3
initial concentrations of HCN = 0.100 M
initial concentrations of NH3 = 0.140 M
At equilibrium, the CN–(aq) concentration is 0.055 M.
Step 2: The balanced equation
HCN(aq) + NH3(aq) ↔ CN-(aq) + NH4+(aq)
Step 3: The concentrations at the equilibrium
For 1 mol HCN we need 1 mol NH3 to produce 1 mol CN- and 1 mol NH4+
[CN-] = [NH4+] = 0.055 M
[HCN] = 0.100 - 0.055 = 0.045 M
[NH3] = 0.140 - 0.055 = 0.085 M
Step 4: Calculate Kc
Kc = [CN-][NH4+] / [HCN][NH3] = (0.055 * 0.055) / (0.045 * 0.085) =0.791
Kc = 0.791
