Transcript Catalyst

Catalyst
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Drill Baby Drill
• Quiz in 45 minutes
• Integrated Practice will by
homework
Quiz
1. Two moles of SO2(g) and seven moles of O2(g) are
introduced into a 1.00 L reaction vessel and allowed to
react to form SO3(g). At equilibrium, the vessel contains
four moles of SO3(g). Calculate Keq for this reaction
2 SO2(g) + O2(g) ⇌ 2 SO3(g)
2. Hydrogen and iodine gases react to form hydrogen
iodide gas. If 6.00 mol of H2 and 3.00 mol of I2 are
placed in a 3.00 L vessel and allowed to come to
equilibrium at 250°C calculate the equilibrium
concentrations of all species. The Keq for the reaction is
4.00 at 250 °C.
H2 (g) + I2 (g) ⇌ 2 HI (g)
Cobalt Chloride Again!
Justify – TPS
• The cobalt chloride equilibrium is as follows:
Co(H2O)62+ + 4 Cl- ⇌ CoCl42- + 6 H2O
Pink
Purple
• Based on this do you believe the heating/cooling
of cobalt chloride indicates that the reaction is
endothermic or exothermic? Justify your
reasoning.
Lecture 7.3 – Le Chatelier’s Principle
Today’s Learning Targets
• LT 7.7 – I can describe and calculate the shift of a chemical
reaction using the reaction quotient (Q)
• LT 7.8 – I can describe the shift of a chemical reaction using
Le Chatelier’s principle. Furthermore, I can explain this shift
in terms of the reaction quotient and common ion effect.
Predicting the Direction of
Reactions
• Oftentimes, we examine reactions prior to them achieving
equilibrium.
• How do we know the direction a reaction needs to move in
order to achieve equilibrium?
• We use the reaction quotient (Q) to determine this
• Q is calculating the equilibrium constant prior to equilibrium:
a A + b B ⇌c C + d D
c
d
[C] [D]
Qc 
a
b
[A] [B]
Value of Q and Direction
• There are three possible results of our Q
calculation:
 Q = K: Reaction is at equilibrium
 Q > K: Amount of products is too large, reaction
needs to shift towards reactants
 Q < K: Amount of reactants is too large, reaction
needs to shift towards products
Class Example
• At 1000 K the value of Kp for the reaction:
2 SO3 (g) ⇌2 SO2 (g) + O2 (g)
• is 0.338. Calculate the value for Qp and predict the direction in
which the reaction proceeds toward equilibrium if the initial
partial pressures are PSO3 = 0.16 atm; PSO2 = 0.41 atm; PO2 =
2.5 atm.
Table Talk
• At 100 oC the equilibrium constant for the reaction:
COCl2 (g)⇌CO (g) + Cl2 (g)
• has the value Kc = 2.19 x 10-10. Are the following mixtures of COCl2,
CO, and Cl2 at 100 oC at equilibrium? [COCl2] = 2.00 x 10-3 M;
[CO] = 3.3 x 10-6 M; [Cl2] = 6.62 x 10-6 M
Le Chatelier’s Principle
• “If a system at equilibrium
is disturbed by a change in
temperature, pressure, or a
component concentration,
the system will shift its
equilibrium position so as to
counteract the effect of the
disturbance”
• When you calculate Q you
are doing the math behind
Le Chatelier’s Principle
Le Chatelier’s Principle and
Concentration
• If we add more of a product/reactant, then our
reaction will shift to the other side in order to
compensate for this new amount.
• Think back to the relationship between Q and K as
the reasoning for this.
Le Chatelier’s Principle and
Volume/Pressure
• Changes in pressure can alter the side of the
reaction that is favored.
• If we increase pressure, the reaction will shift to
the side that produces less molecules
• If we decrease pressure, the reaction will shift to
the side that produces more molecules
Le Chatelier’s Principle and Temperature
• When a reaction is endothermic, heat is listed as a reactant.
Heat + Reactants  Products
• When a reaction is exothermic, heat is listed as a product.
Reactants  Products + Heat
• Therefore we can treat heat like a reactant or a product
depending where it is listed.
Class Example
 Consider the equilibrium:
 In which direction will the equilibrium shift when:
N2O4 (g)⇌2 NO2 (g) ΔHo = 58.0 kJ
(a)N2O4 is added
(b)NO2 is removed
(c)The pressure is increased by addition of N2 (g)
(d)The volume is increased
(e)The temperature is decreased
Table Talk
 For the reaction:
PCl5 (g)⇌PCl3 (g) + Cl2 (g) ΔHo = 87.9 kJ
 In which direction will the equilibrium shift when:
(a)Cl2 (g) is removed
(b)The temperature is decreased
(c)The volume of the reaction system is increased
(d)PCl3 (g) is added
Le Chat. and Catalysts
• A catalyst increases the rate of reaction, but does
not impact final concentrations.
• Therefore, a catalyst does not impact the value
of the equilibrium constant
Relay Race
Relay Race Questions
1. Calculate the reaction quotient for the following equilibrium given that [SO2Cl2]
= 0.108 M, [SO2] = 0.052 M, and [Cl2] = 0.052 M. Given that K = 0.078.
Which direction must the reaction shift in order to achieve equilibrium?
2 SO2 (g) + O2 (g)
2 SO3 (g)
2. For the same equation in problem 1, calculate the reaction quotient given that
that [SO2Cl2] = 0.218 M, [SO2] = 0.52 M, and [Cl2] = 0.042 M. Given that K =
0.078. Which direction must the reaction shift in order to achieve
equilibrium?
State whether it will shift to the left, right, or stay the same based on the given
conditions
NaOH (aq) + HCl (aq)  NaCl (s) + H2O (l)
(1) Add HCl
(2) Remove NaOH
(3) React NaOH with HNO3
State whether it will shift to the left, right, or stay the same based on the given
conditions
NaCl (aq)  Na+ (aq) + Cl- (aq) + 426 kJ
(1) Decrease the temperature
(2) Increase the pressure
(3) Add HCl
⇌
Exit Ticket
1. At 448 oC the equilibrium constant Kc for the
reaction:
H2 (g) + I2 (g)  2 HI (g)
is 50.5. Predict in which direction the reaction
proceeds to reach equilibrium if we start with
2.0 x 10-2 mol of HI, 1.0 x 10-2 mol of H2, and
3.0 x 10-2 mol of I2 in a 2.00 L container.
2. Using the equilibrium in question 1, if the
reaction above is exothermic, then in which
direction will it shift when the reaction vessel is
heated.
Closing Time
• Read: 15.5, 15.6, and 15.7
• Homework: Integrated Free Response Questions