Chemical Equilibrium. The Equilibrium State 01. Chemical Equilibrium: A state achieved when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant.
1. What is the relationship between the concentrations of reactants and products in an equilibrium mixture?
2. Determine equilibrium concentrations from initial concentrations.
3. How to alter the composition of an equilibrium mixture (concentration, pressure, temp, catalyst).
Reversible reactions (arrows in both directions)
Rate of the forward reaction (N2O4 2NO2) decreases as concentration of N2O4 decreases, while the rate of the reverse reaction (N2O4 2NO2) increases as the concentration of NO2increases
What is the relationship between the concentrations of reactants and products in an equilibrium mixture?
aA + bB cC + dD
Equilibrium Constant: Kc = [C]c[D]d products
Kc is independent of concentration changes, but dependent on the temperature.
Kc values are reported without units
Thermodynamic state: [ ] = 1M
Equilibrium Constant: Kc = [NO2]2 = (0.0125M/1M)2
= 4.64 x 10-3 at 25˚C
cC + dD aA + bB
Equilibrium Constant: Kc’ = [A]a[B]b products
Kc = 1/ Kc’
* important to specify the form of the balanced equation
What is the equilibrium equation?
(a) N2(g) + 3H2(g) 2NH3(g)
(b) 2NH3(g) N2(g) + 3H2(g)
aA(g) + bB(g) cC(g) + dD(g)
Equilibrium Constant: Kp = (PC)c(PD)d products
Convert between Kc and Kp using PV = nRT PAV = nART PA = nART = [A]RT
Kp = Kc (RT) ∆n
∆n = moles gas products – moles of gas reactants
1. Write the Kp and Kc expressions for:
2. The equilibrium concentrations for the reaction between CO and Cl2 to form carbonyl chloride (phosgene gas) CO(g) + Cl2(g) COCl2(g) at 74°C are: [CO] = 1.2 x 10–2 M, [Cl2] = 0.054 M, and [COCl2] = 0.14 M. Calculate Kc and Kp.
Methane (CH4) reacts with hydrogen sulfide to yield H2 and carbon disulfide, a solvent used in manufacturing. What is the value of Kp at 1000 K if the partial pressures in an equilibrium mixture at 1000 K are 0.20 atm of CH4, 0.25 atm of H2S, 0.52 atm of CS2, and 0.10 atm of H2?
CaCO3(s) CaO(s) + CO2(g)
Kc = [CO2] because CaCO3 and CaO are solids.
(a) CO2(g) + C(s) 2 CO(g)
(b) Hg(l) + Hg2+(aq) Hg22+(aq)
(c) 2 Fe(s) + 3 H2O(g) Fe2O3(s) + 3 H2(g)
(d) 2 H2O(l) 2 H2(g) + O2(g)Examples 18
H2(g) + I2(g) 2HI(g)
Qc = [HI]t2
Qc > Kc System proceeds to form reactants.Qc = Kc System is at equilibrium.Qc < Kc System proceeds to form products.
The equilibrium constant (Kc) for the formation of nitrosyl chloride, from nitric oxide and chlorine gas:
2 NO(g) + Cl2(g) 2 NOCl(g) is 6.5 x 104 at 35°C. In an experiment, 2.0 x 10–2 moles of NO, 8.3 x 10–3 moles of Cl2, and 6.8 moles of NOCl are mixed in a 2.0-L flask. In which direction will the system proceed to reach equilibrium?