JI
4. N.
2(g)
+O
2(g)
2NO
Nitrogen and oxygen react as illustrated by the equation above to form 1400 ml of nitric oxide gas. The volume
of oxygen which takes part in chemical reactions is :
(a) 800 ml
(b) 700 ml
(c) 600 ml
(d) 850 ml
Answers
Answer:
Explanation:
Chemical equilibrium occurs when a reaction and
its reverse reaction proceed at the same rate.
2
Concept of Equilibrium
• As a system approaches
equilibrium, both the
forward and reverse
reactions are occurring.
• At equilibrium, the
forward and reverse
reactions are proceeding
at the same rate. • Once equilibrium is
achieved, the amount of
each reactant and
product remains
constant.
The same equilibrium is reached whether we
start with only reactants (N2
and H2
) or with
only product (NH3 ).
Equilibrium is reached from either direction. 3
The Equilibrium Constant
• Consider the generalized reaction
The equilibrium expression for this
reaction would be
Kc =
[C]c
[D]d
[A]a
[B]b
aA + bB cC + dD
Since pressure is proportional to
concentration for gases in a closed
system, the equilibrium expression can
also be written
Kp
=
(PC
)c
(PD
)d
(PA
)a
(PB
)b
Chemical equilibrium occurs when
opposing reactions are proceeding at equal rates.
Since, in a system at equilibrium, both the forward
and reverse reactions are being carried out, we
write its equation with a double arrow.
Forward reaction:
N2O4 (g) 2 NO2 (g)
Rate Law:
Rate = kf [N2O4
]
N2O4 (g) 2 NO2 (g)
Reverse reaction:
2 NO2 (g) N2O4 (g)
Rate Law:
Rate = kr [NO2
]2
4
Equilibrium Constant
• Therefore, at equilibrium
Ratef = Rater
kf [N2O4
] = kr [NO2
]2
• Rewriting this, it becomes
kf
kr
[NO2
]2
[N2O4
] =
Keq
=
kf
kr
[NO2
]2
[N2O4
]
= = a constant
Example
N2
(g) + 3 H2
(g) ⇌ 2 NH3
(g)
Write the equilibrium constant expression of the
following reaction:
5
Relationship Between Kc and Kp
Plugging this into the expression for Kp
for each substance, the relationship
between Kc and Kp
becomes
where
Kp = Kc
(RT)n
n = (moles of gaseous product) - (moles of gaseous reactant)
From the Ideal Gas Law we know that:
PV = nRT and P = (n/V)RT = [A]RT
What Does the Value of K Mean?
• If K>>1, the reaction is
product-favored;
product predominates
at equilibrium.
• If K<<1, the reaction is
reactant-favored;
reactant predominates
at equilibrium.
*When 10-3 < K < 103, the reaction is considered to contain a
significant amount of both reactants and products at equilibrium.
6
Direction of Chemical Equation and K
The equilibrium constant of a reaction in the
reverse direction is the reciprocal of the
equilibrium constant of the forward reaction.
Kc = = 0.212 at 100 C
[NO2
]2
[N2O4
] N2O4
(g) 2 NO2
(g)
Kc = = 4.72 at 100 C
[N2O4
]
[NO2
] N2O4 2
2 NO (g) 2
(g)
⇌
⇌
Kc = = 0.212 at 100 C
[NO2
]2
[N2O4
]
Kc = = (0.212)2
at 100 C
[NO2
]4
[N2O4
]2
4 NO2
2 N (g) 2O4
(g)
N2O4
(g) 2 NO2 ⇌ (g)
⇌
The equilibrium constant of a reaction that has
been multiplied by a number, is the equilibrium
constant raised to a power that is equal to that
number.
Stoichiometry and K
7
2 NOBr ⇌ 2 NO + Br2 K1 = 0.014
Br2 + Cl2 ⇌ 2 BrCl K2 = 7.2
2 NOBr + Cl2 ⇌ 2 NO + 2 BrCl
K3 = K1 × K2 = 0.014 × 7.2 = 0.10
The equilibrium constant for a net reaction
made up of two or more steps is the
product of the equilibrium constants for the
individual steps.
Multiple equilibria and K
Example
Consider the following reactions at 1200 K.
CO(g) + 3H2
(g) ⇌ CH4
(