Transcript Slide 1

Equilibrium – Chapter 15
Equilibrium is achieved when forward and
reverse reaction rates are equal.
aA + bB ↔ cC + dD
Watch this animation
http://www.youtube.com/watch?v=LMIbJ-B92Ho
[X] = concentration of species X in molarity
Px = pressure of gas X in atmospheres
ex Write the equilibrium constant for the
following reaction:
2NO(g) + Cl2(g) ↔ 2NOCl(g)
ex The reaction of N2 with O2 to form NO might
be considered a means of "fixing" nitrogen:
N2(g) + O2(g) ↔ 2NO(g)
Determine the K for:
2NO ↔ N2 + O2
for
4NO ↔ 2N2 + 2O2
Kp is the equilibrium expression in terms of
pressure for a reaction involving only gases. It is
not necessarily equal to Kc.
Kp = Kc(RT)Δn
Δn = sum of the coefficients of the gas products sum of the coefficients of the gas reactants.
ex SnO2(s) + 2CO(g) ↔ Sn(s) + 2CO2(g)
Applications of K
K >> 1
K << 1
equilibrium lies to the right,
products favored
equilibrium lies to the left,
reactants favored
Important:
The size of K and the time to reach
equilibrium are NOT related.
Link to simulation
http://www.mhhe.c
om/physsci/chemist
ry/animations/chang
_7e_esp/kim2s2_5.s
wf
Prediction of the direction of a reaction
Reaction quotient, Q, takes the same form
as K but is the expression at a given time, not
necessarily at equilibrium.
Q>K
Q=K
Q<K
←
equilibrium
→
Ex - At 448oC the equilibrium constant for the
following reaction, Kc, is 50.5.
H2(g) + I2(g) ↔ 2HI
Predict the direction in which the reaction will
proceed to reach equilibrium at 448oC if we start
with 0.020 mol of HI, 0.010 mol of H2 and 0.030
mol of I2 in a 2.0 L container.
Calculation of Equilibrium Concentrations
ex For the Haber process,
N2(g) + 3H2(g) ↔ 2NH3(g)
Kp = 1.45x10-5 at 500oC. In an equilibrium mixture
of the three gases at 500oC, the partial pressure
of H2 is 0.928 atm and that of N2 is 0.432 atm.
What is the partial pressure of NH3 in the
equilibrium mixture?
ex A 1.000 L flask is filled with 1.000 mol of H2
and 2.000 mol of I2 at 448oC. The value of Kc at
this temperature is 50.5. What are the
equilibrium concentrations of H2, I2, and HI?
Here is the quiz
https://docs.google.com/spreadsheet/embeddedform?formkey=dDM4ODY2LWJKVGdX
M2dnQXdkTjBrbUE6MQ