chemical equilibrium q, k, and calculations chapter 16
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Chemical Equilibrium Q, K, and Calculations Chapter 16. Equilibrium. the forward and reverse reactions proceed at equal rates the concentrations of reactants and products are constant = Can be reached from either direction (starting with either “reactants” or “products” has the same result). - PowerPoint PPT PresentationTRANSCRIPT
Chemical Equilibrium Q, K, and
Calculations Chapter 16
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Equilibrium• the forward and reverse reactions proceed at
equal rates• the concentrations of reactants and products
are constant =• Can be reached from either direction
(starting with either “reactants” or “products” has the same result)
CO + 3H2CH4 + H2O
Example Reaction
CO + 3 H2 CH4 + H2O
Q and K
• Reaction Quotient: Q– Describes a rxn at _____________
• Equilibrium Constant: K– Describes a rxn at _____________
• Both values are calculated from the same expression
K =[C]c [D]d
[A]a [B]b
conc. of products
conc. of reactantsequilibrium constant
c
a A(aq) + b B(aq) c C (aq) + d D(aq)
For a general reaction occurring __________:
[ ] = molarity
Equilibrium Constant Expression
Equilibrium Constant Expressions
• The exponents are based on the __________!!
• ________ OVER _______
• There are no _____ for Q or K
When writing the expressions
• Include only these phases: ___ + ____
• Omit these phases: ____+ ____
• For reactions of __________:
Kp = PC PD
PA PB
c d
a b
P = partail pressure of the gas
a A(g) + b B(g) c C (g) + d D(g)
Q and K
• If concentrations or partial pressures represent the reaction at equilibrium, you can calculate ______.
• If concentrations or partial pressures represent the reaction at any time, you can calculate ______.
Write the equilibrium expression
1) N2(g) + 3H2 (g) <----> 2NH3 (l) (Kp)
2) CO(g) + 3H2(g) <----> CH4(g) + H2O(g) (Kc & Kp)
2 Red(g) <----> Blue (g)
• Write the expression for Kc and Kp
• Applet
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PCl3(g) + Cl2(g) <--> PCl5(g) Kc = [PCl5] [PCl3][Cl2]
Different amounts of R & P are mixed at 546 K to determine K
Calculating K
Comment on the equilibrium position.
Calculating K
H2(g) + I2(g) <---> 2HI
• At equilibrium, the concentration for both H2 and I2 = 0.0037 M and HI = 0.0276. Write the expression for K and calculate its value? What this value mean?
• K > 1 the reaction is ________ favored• K< 1 the reaction is ________ favored
Calculating Q
• H2(g) + I2(g) <---> 2HI
• 2 moles each of H2 and I2 and 3 moles of HI are placed in a 0.5 L flask. Determine if the rxn is at equilbrium? If not will it move forward or reverse?
• Q = K the reaction _______________
• Q < K the reaction ________________
• Q > K the reaction ________________
Kc and Kp are related
• Kp = Kc(RT)∆n
• R= 0.08206 Liter atm mol K
• ∆n = # product gases - # reactant gases
• H2(g) + I2(g) <---> 2HI
• If Kc = 56, calculate Kp at 25 °C.
Kp = Kc(RT)∆n
A real one! Kp = Kc(RT)∆n
• N2(g) + 3 H2(g) <---> 2NH3(g)
• The Kp = 5.8 x105, calculate Kc at 25 °C.
MORE ABOUT K!!!!
• K values for various forms of a balanced equation relate to the coefficients
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The K value for the reverse rxn is the ______________
Multiplying a reaction by a # _______________
MORE ABOUT K!!!!
at 298 K
C(s) + 1/2 O2(g) <---> CO(g) K1 = 4.6 X 1023
2 C (s) + O2 (g) <--> 2CO(g) K2 = ?
MORE ABOUT K!!!!
• When adding reactions to produce a net equation, ________ K values.
• For a 2 reactions, with K1 and K2, Knet = K1K2