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H2(g) + I2(g) <--> 2HI(g)
• Write the K expression
• [H2] = 0.106 M
• [I2] = 0.022 M
• [HI] = 1.29 M
H2(g) + I2(g) <--> 2HI(g)
• What is the equilibrium
conc of [HI] if:
• [H2] = 0.81 M
• [I2] = 0.035 M
Solve for K if:
• It is the reverse rxn
• The eqn is 1/3 of the
original
• The eqn is reversed and
is 4 times the original.
Equilibria with pressures?
• So far, we’ve only used
concentration
• gases can be described
in terms of pressures
PV = nRT
• P =(n/V]RT = CRT
• C= molar conc of gas
• Kp is the equilibrium in
terms of partial
pressures of the gases
N2(g) + 3H2(g) <--> 2NH3(g)
• Write the Kp expression
• How do K and Kp relate?
• Let’s try it for this rxn…
2
• K= Kp(RT)
H2(g) + F2(g) <--> 2HF(g)
• Try it for this rxn…
• K = Kp
• b/c sum of coefficients
on either side is equal
General relationship
• Kp
n
= K(RT)
• n= the sum of the
coefficients of the gaseous
products minus the sum of
the coefficients of the
gaseous reactants
CH3OH(g) <-> CO(g) + 2H2(g)
• At 25oC
-4
• PCH3OH = 6.10 x 10 atm
• PCO = 0.387 atm
• PH2 = 1.34 atm
• What is K?
So far...
• Our systems have only
involved gases!
• Homogeneous equilibriawhere phases are all the
same
Heterogeneous equilibria
• Equilibria involving more
than one phase
• Take for instance…
• CaCO3(s) <-> CaO(s) + CO2(g)
• Write the K
However...
• Experiments show that the
position of heterogeneous
equilibrium does not depend
on the amounts of pure
solids or liquids present!!
Why??
• Concentrations of pure
solids and liquids can
NOT change!!
• So… LEAVE THEM OUT of K!!
• Let’s try…
Homework
• P 640 (WOW!)
• 22, 25, 28, 29, 31
To do now…
• Learn how to use
“assignments” folder
• set groups for presentations
• set up chem olympics teams
• start homework!