Aim # 25: What is chemical equilibrium?
H.W. # 25
Study pp. 543-547 (sec. 17.4-17.5)
pp. 548-551 (sec. 17.6)
Ans. ques. p. 570 # 11-15,18
p.571 # 22
p. 567 # 2
2H2 + O2 → 2H2O
H2 + I2 ↔ 2HI
I Reversible Reaction - a reaction in which the
products can react, under suitable conditions, to
produce the original reactants.
e.g. 2SO2(g) + O2(g) → 2SO3(g)
BUT, when SO3(g) is placed in a container
by itself,
2SO3(g) → 2SO2(g) + O2(g)
II In the container below, count the number
of each type of molecule.
= O2
= SO2
= SO3
A. SO2(g) + O2(g) → SO3(g)
or
SO3(g) → SO2(g) + O2(g)
Which reaction will be faster?
B. How will the quantities of each
gas change over time?
C. How will the rates of the two
reactions change over time?
Equilibrium- a state of balance between two
opposing reactions occurring at the same time.
e.g. 2SO2(g) + O2(g) ↔ 2SO3(g)
forward rate = reverse rate
III For a reaction at equilibrium at constant
temperature,
the balanced equation is
aA + bB ↔ cC + dD
and the equilibrium constant is defined as
Keq = [C]c x [D]d
[A]a x [B]b
Where
Keq = is the equilibrium constant
[A] and [B] are reactant concentrations
[C] and [D] are product concentrations
a,b,c, and d are the coefficients of the
balanced equation for the reaction
For the reaction
N2(g) +3H2(g) ↔ 2NH3
Keq = [NH3]2
[N2][H2]3
Write equilibrium constant expressions for
each of the following equations:
1. 2SO2(g) + O2(g) ↔ 2SO3(g)
2. PCl5(g) ↔ PCl3(g) + Cl2(g)
3. N2O4(g) ↔ 2NO2(g)
IV The magnitude of Keq predicts the
position of the equilibrium for the reaction.
A. A large value for Keq favors the
production of products.
B. A small value of Keq favors the
production of reactants.
V A change in temperature will cause a
change in the value of Keq.
e.g. For H2(g) + I2(g) ↔ 2HI(g)
at 4900C Keq = 45.9
at 4000C Keq = 54.5