Download Chemical Equilibrium Equilibrium A state where the reactants and

Chemical Equilibrium
Equilibrium
 A state where the reactants and products remain ____________________ over time.
 For some reactions, the equilibrium position favors the _____________ and the reaction
appears to have gone to _______________ (amount of reactants is _______________)”Equilibrium lies to the right” (in direction of the _______________)
Example: 2 H2 + O2  2 H2O
 Other reactions only occur to a ______________ extent with the product virtually ___________”Equilibrium lies to the left” (in direction of the _________________)
Example: 2 CaO  2Ca + O2
 Equilibrium is not _____________
 Because the concentrations do not change, it appears that the reaction has _____________.
 Instead, equilibrium is highly ________________ with the reactions continuing to occur in _____
directions at the ___________________.
Products
Reactants
 As the concentration of the reactants ____________________, the forward reaction
______________.
 As the concentration of the products _____________________, the rate of the reverse reaction
________________.
 Eventually the rates become _________________.
Factors affecting equilibrium position:
 _____________ concentrations***
 ________________ of reactants and products
 “____________________” of reactants and products.
***The factor to be addressed in this unit.
Equilibrium Constants
 Through __________________ and observation, the _________________________________
was proposed.
 The law suggests that for a reaction of the following type:
jA + kB  lC + mD
the following equilibrium expression is used to represent the reaction.
K = [C]l [D]m
[A]j [B]k
Practice
 Write the equilibrium expression for the following equation:
4 NH3 + 7 O2 < -- > 4 NO2 + 6 H2O
Determining the Equilibrium Constant
 The equilibrium constant can be calculated at a given ___________________ if the equilibrium
concentrations of the reaction components are known.
N2 + 3H2 < -- > 2 NH3
-2
[NH3] = 3.1 x 10 M
[N2] = 8.5 x 10-1 M
[H2] = 3.1 x 10-3 M

Calculate the value for K
Other methods for Determining Equilibrium Constants
 If the reaction is reversed,
2NH3 < --> N2 + 3H2
then, K/ =

If the reaction is multiplied by a factor,
½ N2 + 3/2 H2 < -- > NH3
then, K// =
Application from the lab
 At a given temperature:
1) K always has the _____________________ regardless of the starting __________________
2) the equilibrium concentrations will _________ always be the __________
(The set of equilibrium concentrations is called the ________________ ________________.)
 There is only _______ equilibrium constant at a particular ________________, but there is an
____________ number of equilibrium ___________________.
 The ___________ equilibrium position depends on the __________________ concentrations,
but the equilibrium _____________ does _____.
 See example 13.3
Heterogeneous Equilibrium
 Many reactions involve reaction components in more than __________________.
Example: CaCO3 (s) < -- > CaO (s) +CO2 (g)

Because the concentrations of pure ___________ and _________________ cannot change, they
are ________ included in the equilibrium expression.

So, K = [CO2]

Write the equilibrium expression for the following equation:
PCl5(s) < -- > PCl3(l) + Cl2(g)
Equilibrium Involving Pressure
 Equilibrium involving ___________ can be described in terms of _________________ (as well as
___________________)
 PV = nRT or P = (n/V)RT where n/V is the concentration of the gas.
 The equilibrium constant in terms of partial pressures in written as _______
Sample Problem
 Given the following reaction:
2NO(g) + Cl2 (g) < -- > 2NOCl(g)
PNOCl = 1.2 atm
PNO = 0.050 atm
PCl2 = 0.30 atm
 Calculate the value of Kp
Relationship between K and KP
 KP = K(RT)Δn
(see pages 587-588 to view how this equation was derived)
R = 0.08206
T is the temperature in Kelvin
Δn = the difference in the sum of the coefficients for the products and the reactants.
 Example: jA + kB < -- > lC + mD
Δn =
Sample Problem
 Using the value for Kp obtained in the previous sample problem, calculate the value of K for the
reaction
2NO(g) + Cl2(g) < -- > 2NOCl(g)
Applications of the Equilibrium Constant
 Knowing the equilibrium constant allows us to predict several important features of the
reaction.
1) the tendency of the reaction to ___________ (but not the _______________)
2) whether a given set of concentrations represent an __________________ condition
3) the equilibrium position that will be achieved from a given set of __________ concentrations.
The Extent of a Reaction
 The tendency for a reaction to occur is indicated by the __________ of the equilibrium constant.
 A value of K much _________ than 1 means that at equilibrium the reaction will consist mostly
of ____________-the equilibrium lies to the _____. (The reaction goes to _________________)
 A value of K much _________ than 1 means that at equilibrium the reaction will consist mostly
of ___________-the equilibrium lies to the _____. (The reaction does not occur to any given
extent)
 The _____ of K and the ______ required to reach equilibrium are _______ directly related.
Reaction Quotient
 When given a set of reaction components, it is helpful to know if the mixture is at equilibrium
or, if not, in what __________ the system must shift to reach equilibrium.
 To determine the direction of the move toward equilibrium, we use the __________ _________
(Q).
 The reaction quotient is obtained by applying the law of mass action to the _________
concentrations instead of ____________ concentrations.
 If Q = K, the system is at equilibrium; _____ shift will occur
 If Q > K, the system shifts to the _________.
 If Q < K, the system shifts to the _________.
Complete the sample problem on page 593.
Le Chatelier’s Principle
 Le Chatelier’s Principle states that if a _________ is imposed on a system at equilibrium, the
position of equilibrium will ________ in a direction that tends to __________ that change.
Effect of a Change in Concentration
 If a component is ______________ to a reaction system at equilibrium (at constant T and P), the
equilibrium position will shift in the direction that ____________ the concentration of that
component (_____ ______).
 If a component is _____________ from the system, the system will shift in the direction that
______________ the concentration of that component (___________)
Copy the following equation:
As4O6(s) + 6C(s) < -- > As4(g) + 6CO (g)
Q1. In which direction will the equilibrium position shift if CO is added?
1. Left
2. Right
3. No shift will occur
Q2. In which direction will the equilibrium position shift if C is removed?
1. Left
2. Right
3. No shift will occur
Q3. In which direction will the equilibrium position shift if CO is removed?
1. Left
2. Right
3. No shift will occur
Effect of a Change in Pressure
 Adding an _____ gas has ____ effect on the equilibrium position (has no effect on the
concentrations or partial pressures of the reactants or products).
 Increasing the _______ of the container _________the pressure. The system responds by
increasing the pressure through the production of ______ gaseous molecules (a shift toward the
side with the __________ number of gas molecules).
 Decreasing the volume of the container results in the ________ occurrence.
Q4. What shift in the equilibrium position will occur if the volume is reduced for the following process:
P4(s) + 6Cl2(g) < -- > 4PCl3(l)
1. Left
2. Right
3. No shift will occur
Q5. What shift in the equilibrium position will occur if the volume is reduced for the following process:
PCl3 (g) + Cl2 (g) < -- > PCl5 (g)
1. Left
2. Right
3. No shift will occur
Q6. What shift in the equilibrium position will occur if the volume is reduced for the following process:
PCl3(g) + 3NH3(g) < -- > P(NH2)3(g) + 3HCl(g)
1.
Left
2. Right
3. No shift will occur
Effect of a Change in Temperature
 Changing the temperature changes the value of _____.
 In ____________reactions (heat is _______________ and is therefore written as a _________),
the equilibrium position will shift to the ______ if the temperature is ___________ and to the
_________ if the temperature is _________________.
 For __________________reactions, the _______________ will occur.
Q7. For the following reaction, predict how the value of K changes as the temperature is increased.
N2(g) + O2(g) < -- > 2NO(g) ΔH = 181 kJ
1. Increases
2. Decreases
3. Remains the same
Q8. For the following reaction, predict how the value of K changes as the temperature in increased.
2SO2(g) + O2(g) < -- > 2SO3(g) ΔH = -198 kJ
1. Increases
2. Decreases
3. Remains the same
Copy the following equation
N2(g) + 3H2(g) < -- > 2NH3(g) + 92.94 kJ
Q9. How will the equilibrium position shift if the temperature increases?
1. Left
2. Right
3. No shift will occur
Q10. How will the equilibrium position shift if the volume increases?
1. Left
2. Right
3. No shift will occur
Q11. How will the equilibrium position shift if NH3 is removed?
1. Left
2. Right
3. No shift will occur
Q12. How will the equilibrium position shift if N2 is added?
1. Left
2. Right
3. No shift will occur
Q13. How will the equilibrium position shift if some Ar(g) is added?
1. Left
2. Right
3. No shift will occur
Homework
All homework problems that accompany Chapter 13 should be completed for class tomorrow.