Module 3 - Chemical Equilibrium Flashcards
What does dynamic
equilibrium mean?
It occurs when the rate of forward reaction equals
the rate of reverse reaction and the concentration of
reactants and products remain constant in a closed
system
Changing what factors can
alter the position of
equilibrium?
● Concentration of reactants or products
● Pressure
● temperature
Explain the Le Chatelier’s
principle
If a system at equilibrium is disturbed,
the equilibrium moves in the direction
that tends to reduce the disturbance.
In the equation:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol -1
What effect would increasing the temperature have
on the position of equilibrium?
The equilibrium position shifts to the right.
(This is because the forward reaction is
endothermic. Yield of hydrogen increases.)
In the equation:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol-1
What effect would increasing the pressure
have on the position of equilibrium?
The equilibrium position shifts to the left.
This is because the forward reaction is produces
more moles of gas than the reverse reaction (4
moles of product, 2 moles of reactant). Therefore
the yield of hydrogen decreases.
The reaction:
CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol-1
Suggest and explain why an industrial chemist may
use a high pressure for this production of hydrogen
from the above reaction?
The high pressure increases the collision frequency
thus increasing the rate of reaction.
This is a compromise pressure between an
economically viable rate of reaction and a slightly
lower yield of hydrogen
What effect does a catalyst
have on the position of
equilibrium?
No effect.
(because catalyst affects rate of forward
and reverse reactions equally)
What condition affects the value of Kc?
❑ Concentration
❑ Catalyst
❑ Pressure
❑ Temperature
❑ Temperature
For the reaction below, deduce an
expression for Kc .
2[A] + 3[B] + [C] ⇌ [D]+ 4[E]
kc= [D][E]^2 / [A]^2[B]^3[C]
Deduce units for the value of kc= [D][E]^2 / [A]^2[B]^3[C]
mol-1 dm-3
What type of system is Kc
relevant for?
Homogeneous systems in equilibrium
What does Kc
being greater
or less than 1 suggest for
the position of equilibrium?
Greater than 1 = over to the right
Less than 1 = over to the left
What effect does decreasing
the temperature of an
endothermic reaction have on
Kc ?
Kc decreases
What effect does increasing
the temperature of an
endothermic reaction have on
Kc ?
Kc
increases
What effect does decreasing
the temperature of an
exothermic reaction have on
Kc ?
Kc
increases
