Topic 1: Chemical equilibrium systems
SYLLABUS: NOTES: EXAMPLES & TIPs & EVERYTHING THAT IS HELPFUL:
Science Chemical Equilibrium:
understanding: Open system exchange energy and matter with the surroundings.
The following
subject matter Closed systems exchange only energy and NOT MATTER.
can be assessed
in the external The two arrows shows that the reaction is reversible:
assessment. H 2 O ( l) ⇌ H 2 O ( g )
Chemical
equilibrium Reversible reactions are reactions that can go either in the forward
direction or the reverse direction:
• Discriminate N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 ( g)
between open
or closed Equilibrium: Understanding of the graph:
chemical In a closed system a reversible reaction When the concentration of the reactant is
systems. will eventually reach a situation where decreasing and the product increasing, this process
no further change can be observed. was required as there were none of the products
• Identify that The system is described as having produced and now at equilibrium, we have enough
physical reached equilibrium. products to turn back into reactants.
changes are
usually
reversible, Equilibrium established is when the concentration of both products
whereas only and reactants is constant.
some chemical N 2 ( g) +2 H 2 (g ) ⇌ 2 N H 3 ( g)
reactions are
reversible. Dynamic Equilibrium:
At dynamic equilibrium, macroscopic properties are constant:
• Symbolise concentration of reactants and products remains constant.
equilibrium
equations using The rate of the forward reaction is equal to the rate of the reverse
⇋ in balanced reaction.
chemical
equations. Activation energy: minimum energy required for colliding particles to
possess in order for a reaction to occur, energy required to break the
• Explain
,observable bonds of the reactants and allow formation of product. Calculate the mole of N 2 O4:
properties and Since concentration of N O2 increased from 0 to
the n
0.08 mol/L, [ N O2 ]=
characteristics V
of physical and n=[ N O2 ] V
chemical ¿ 0.08 ×1
systems in a ¿ 0.08 mol N O2
state of 1
n N O =0.08 ×
equilibrium. 2 4
2
¿ 0.04 mol
• Explain that, Also, initial [N 2 O4 ] is 0.07mol/L, and final [N 2 O4 ] is
over time, 0.03mol/L:
physical change 0.07−0.03
and reversible ¿ 0.04 mol L
−1
chemical n=0.04 ×1
If the product particles collide with enough energy to break the bonds,
reactions reach ¿ 0.04 mol 😊
then it is possible to re-form the original reactants.
a state of
H 2 ( g) + I 2( g ) ⇌ 2 H I (g )
dynamic
equilibrium in a
closed system,
with the relative
concentrations
of products and
reactants
defining the
position of
equilibrium.
What did the scientist do at 15min?
• Explain the You can see that there is a really steep drop with F 2
reversibility of Rate of forward reaction starts At the start, many reactants which means that concentration of F 2 is lowered.
chemical off fast and begins to slow as the (H 2∧I 2) and no products (2 HI ). This unbalances the ratio of the equation (e.g. as
reactions by concentration of the reactants the ratio of the equation is 1:1:1 and decreasing F 2
considering the decrease make it 2:1:2 so unbalanced), therefore, more
activation After equilibrium reached; rate No longer a change in the CO F 2 was formed into the products as seen in the
energies of the of forward = rate of reverse. amounts of reactants and graph.
forward and products.
, reverse
reactions.
Factors that affect equilibrium:
• Analyse data Le Chatelier’s Definition: What happens when the temperature is increased
and interpret If a closed system at equilibrium is disturbed, then the system adjusts in a system of equilibrium?
graphical itself so as to minimise the disturbance.
representations N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
of relative Temperature:
changes in the N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
Using this example:
concentration In forward reaction, heat is given to the
of reactants and This rection is exothermic (heat is a product) environment (exothermic).
product against
time, to ∴ N 2( g) +3 H 2(g ) ⇌ 2 N H 3( g) + Heat In reverse reaction heat is taken from the
determine the environment (endothermic).
position of This means that as it proceeds from left to right when heat is liberated
equilibrium. and removed from the system. Increasing the temperature increases the heat
Factors that (product). Therefore, more heat results in higher
affect If we increase the temperature at constant pressure the equilibrium rate of reverse reaction.
equilibrium moves to the left, because that is the direction that absorbs heat and
so tends to counteract the temperature increase. Therefore, more products will reform back into
• Determine the reactants then the number of reactant particles will
effect of This graph shows a increase, resulting in increased rate of forward
temperature decrease in reaction (exothermic).
change on temperature as the
chemical concentration changes However, increase in rate of forward reaction is not
systems at without any steep directly caused by increase in temperature. This
equilibrium by increase to reach a new causes the system to reach a new equilibrium.
considering the equilibrium
enthalpy
change for the What happens when the concentration is increased
forward and in a system of equilibrium?
reverse
reactions. At higher temperatures, the rates of both the forward and reverse N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
reactions increase.
• Explain the In this case: Increased concentration of N 2 will increase the rate
effect of N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol of forward reaction which increases the number of
SYLLABUS: NOTES: EXAMPLES & TIPs & EVERYTHING THAT IS HELPFUL:
Science Chemical Equilibrium:
understanding: Open system exchange energy and matter with the surroundings.
The following
subject matter Closed systems exchange only energy and NOT MATTER.
can be assessed
in the external The two arrows shows that the reaction is reversible:
assessment. H 2 O ( l) ⇌ H 2 O ( g )
Chemical
equilibrium Reversible reactions are reactions that can go either in the forward
direction or the reverse direction:
• Discriminate N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 ( g)
between open
or closed Equilibrium: Understanding of the graph:
chemical In a closed system a reversible reaction When the concentration of the reactant is
systems. will eventually reach a situation where decreasing and the product increasing, this process
no further change can be observed. was required as there were none of the products
• Identify that The system is described as having produced and now at equilibrium, we have enough
physical reached equilibrium. products to turn back into reactants.
changes are
usually
reversible, Equilibrium established is when the concentration of both products
whereas only and reactants is constant.
some chemical N 2 ( g) +2 H 2 (g ) ⇌ 2 N H 3 ( g)
reactions are
reversible. Dynamic Equilibrium:
At dynamic equilibrium, macroscopic properties are constant:
• Symbolise concentration of reactants and products remains constant.
equilibrium
equations using The rate of the forward reaction is equal to the rate of the reverse
⇋ in balanced reaction.
chemical
equations. Activation energy: minimum energy required for colliding particles to
possess in order for a reaction to occur, energy required to break the
• Explain
,observable bonds of the reactants and allow formation of product. Calculate the mole of N 2 O4:
properties and Since concentration of N O2 increased from 0 to
the n
0.08 mol/L, [ N O2 ]=
characteristics V
of physical and n=[ N O2 ] V
chemical ¿ 0.08 ×1
systems in a ¿ 0.08 mol N O2
state of 1
n N O =0.08 ×
equilibrium. 2 4
2
¿ 0.04 mol
• Explain that, Also, initial [N 2 O4 ] is 0.07mol/L, and final [N 2 O4 ] is
over time, 0.03mol/L:
physical change 0.07−0.03
and reversible ¿ 0.04 mol L
−1
chemical n=0.04 ×1
If the product particles collide with enough energy to break the bonds,
reactions reach ¿ 0.04 mol 😊
then it is possible to re-form the original reactants.
a state of
H 2 ( g) + I 2( g ) ⇌ 2 H I (g )
dynamic
equilibrium in a
closed system,
with the relative
concentrations
of products and
reactants
defining the
position of
equilibrium.
What did the scientist do at 15min?
• Explain the You can see that there is a really steep drop with F 2
reversibility of Rate of forward reaction starts At the start, many reactants which means that concentration of F 2 is lowered.
chemical off fast and begins to slow as the (H 2∧I 2) and no products (2 HI ). This unbalances the ratio of the equation (e.g. as
reactions by concentration of the reactants the ratio of the equation is 1:1:1 and decreasing F 2
considering the decrease make it 2:1:2 so unbalanced), therefore, more
activation After equilibrium reached; rate No longer a change in the CO F 2 was formed into the products as seen in the
energies of the of forward = rate of reverse. amounts of reactants and graph.
forward and products.
, reverse
reactions.
Factors that affect equilibrium:
• Analyse data Le Chatelier’s Definition: What happens when the temperature is increased
and interpret If a closed system at equilibrium is disturbed, then the system adjusts in a system of equilibrium?
graphical itself so as to minimise the disturbance.
representations N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
of relative Temperature:
changes in the N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
Using this example:
concentration In forward reaction, heat is given to the
of reactants and This rection is exothermic (heat is a product) environment (exothermic).
product against
time, to ∴ N 2( g) +3 H 2(g ) ⇌ 2 N H 3( g) + Heat In reverse reaction heat is taken from the
determine the environment (endothermic).
position of This means that as it proceeds from left to right when heat is liberated
equilibrium. and removed from the system. Increasing the temperature increases the heat
Factors that (product). Therefore, more heat results in higher
affect If we increase the temperature at constant pressure the equilibrium rate of reverse reaction.
equilibrium moves to the left, because that is the direction that absorbs heat and
so tends to counteract the temperature increase. Therefore, more products will reform back into
• Determine the reactants then the number of reactant particles will
effect of This graph shows a increase, resulting in increased rate of forward
temperature decrease in reaction (exothermic).
change on temperature as the
chemical concentration changes However, increase in rate of forward reaction is not
systems at without any steep directly caused by increase in temperature. This
equilibrium by increase to reach a new causes the system to reach a new equilibrium.
considering the equilibrium
enthalpy
change for the What happens when the concentration is increased
forward and in a system of equilibrium?
reverse
reactions. At higher temperatures, the rates of both the forward and reverse N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol
reactions increase.
• Explain the In this case: Increased concentration of N 2 will increase the rate
effect of N 2 (g) +3 H 2(g ) ⇌ 2 N H 3 (g) ∆ H=−92 kJ /mol of forward reaction which increases the number of
