Chapter 12:. Chemical Equilibrium. The Dynamic Nature of Equilibrium. A. What is equilibrium? 1. Definition a state of balance; no net change in a dynamic process. 2. Definition of chemical equilibrium.
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No net change with the total amount of reactants and products remaining constant, while the reaction continues
Eek = equilibrium
Reactants Products = Products Reactants
Like all good things, it takes time!
[A]a [B]b Molarities
N2(g) + O2(g) 2 NO(g) Keq=55
N2(g) + 3H2(g) 2NH3(g) Keq=5x10-6
A(g) + B(g) C(g)
The Keq of summed reactions will be the product of the Keq’s
If you multiply the coefficients in an equation by a factor you must raise Keq to the power of that factor
A(g) + B(g) C(g) Kp=3
A(g) + B(g) D(g) Kp=6
What is the Kp for C(g) D(g)?
½ N2(g)+ ½ O2(g)NO(g) Keq=6.9x10-16
NO2(g) NO(g) + ½ O2(g) Keq=6.7x10-7
N2O4(g) 2NO2(g) Keq=0.15
What is the Keq for N2(g)+2O2(g)N2O4(g)
Rule: Systems where all the substances are not in the same phase of matter. Specifically, the reaction includes at least one pure solid or liquid which would not be included in the Keq expression.
a. Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)
b. CaCO3(s) CaO(s) + CO2(g)
Kp = Kc(RT)∆ng
PCl3(g) + Cl2(g) PCl5(g)
The equilibrium concentration of phosphorus pentachloride is 2.59 mole/L. What are the equilibrium concentrations of the other two gases? Calculate Keq for the above reaction system.
2NO(g) + Br2(g) 2NOBr(g)
At a given temperature, 1.6 mol of NO and 1.6 mol of Br2 are added to a 1.00 Liter flask and the equilibrium concentration of NOBr is found to be 0.53 mol/L. Calculate the equilibrium concentrations of the other 2 gases and the value of Keq.
Description of problems:
set one of the “R” values as X and determine the others by their mole (coefficient) relationships
(Direction of Shift to Reach Equilibrium)
a. Q = the same expression as for Keq
The values for each substance are not equilibrium values but the actual concentrations at any moment in time.
c. If Q = Kc , then the system is at equilibrium
d. If Q > Kc , then the reaction will proceed to the left
“When a system is stressed (changes in concentration, temp, gas pressure, or volume of container), the system will respond by attaining new equilibrium conditions that counteract the change”