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.
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.
Example: Write the K greater proportion? Answer in a complete sentence.eq for:
a. Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)
b. CaCO3(s) CaO(s) + CO2(g)
Kp = Kc(RT)∆ng
Example: When 4.29 moles of PCl greater proportion? Answer in a complete sentence.3(g) and 4.29 moles of Cl2(g) are placed in a 1.00 Liter container at 250oC, the following equilibrium is established:
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.
Example: Consider the equilibrium system: greater proportion? Answer in a complete sentence.
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.
b. If Q < K greater proportion? Answer in a complete sentence.c , then the reaction will proceed to the right
c. If Q = Kc , then the system is at equilibrium
d. If Q > Kc , then the reaction will proceed to the left
Example: For N greater proportion? Answer in a complete sentence.2O4(g)2NO2(g) Kc=11.0 at 100°C. Is the system at equilibrium if the concentration of both gases is 0.20M? In which direction will the system shift to reach equilibrium?
Example: Answer the same question for the system above if the gas concentrations are 0.07M for N2O4 and 1.00M for NO2.
If the system is started with 0.50 mol of each of the reactants and 9.30 mole of the HI in a 5.0L container, predict the direction the system will shift to reach equilibrium.
“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”