Chemical Equilibrium: [Concentration] vs. Time

Chemical Equilibrium: Rate vs. Time

CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

Stress: [CO]

( CO is added to the system)

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• Sharp increase in CO; then decreases due to shift right (some of the added CO is consumed)
• Cl₂ is consumed( [ ] decreases) as the reaction shifts right
• COCl₂ is produced( [ ] increases) as the reaction shifts right
• System returns to equilibrium (Kc constant because temperature is constant)

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One spike!

Stress: [CO]

( CO is added to the system)

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• Sharp increase in the forward reaction as the system shifts right
• Reverse reaction shoes a slow increase due to the increase in [ ] (rate of any chemical reaction increases with an increase in [ ] and/or temperature
• Equilibrium is reestablished; rate of forward and reverse are equal at a higher rate

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CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

One spike!

Stress: increase [CO] (CO is added)

One spike!

One spike!

CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

Stress: Temperature

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• All of reactants and products have a gradual change
• Reactions shifts right
• [CO] and [Cl₂] decrease as they are consumed
• [COCl₂] increases as it is produced
• System returns to equilibrium (Kc has increased because temperature changed and there are now more products)

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All change

CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

Stress: Temperature

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• Both the forward and reverse reactions decrease due to a decrease in temperature
• The reaction shifts right so the forward reaction begins to increase (recovers some of its speed due to the shift)
• Equilibrium is reestablished at a lower rate ( rate of forward and reverse reactions are again equal)

Both Change!!

Stress: Temperature is decreased

All change!!

Both Change!!

CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

All sharp change!!

Stress: Decrease in Volume

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• A decrease in volume causes all concentrations to increase
• Reaction shifts right
• [CO] and [Cl₂] decrease
• [COCl₂] increases
• Equilibrium is reestablished
• Kc is constant ( temperature has not changed)

CO_(g) + Cl_{2 (g)} → COCl_{2 (g)}+ energy

Both sharp change!!

Stress: Decrease in Volume

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• A decrease in volume causes all rates to increase (a decrease in volume increases the concentration of all; rate increases when concentration increases.
• Reaction shifts right
• Rate of forward reaction increases more (due to shift right)
• Rate of the reverse reaction increases less (due to shift right)
• Equilibrium is reestablished (rates are equal at a higher rate due to higher concentration)

Stress: Decrease in Volume

** For volume changes when the number of gas moles of reactants and products are equal….. There is no shift; so the graphs would look as follows:

All sharp change!!

Then equilibrium is reestablished with no shift

All sharp change!!

Then equilibrium is reestablished with no shift

Stress: Volume

Stress: Catalyst is added

A system already at equilibrium will not have its concentrations affected by a catalyst

A system already at equilibrium will have the rate of both the forward and reverse reactions increase at the same rate; equilibrium is reestablished at a higher rate

Practice Problems:

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1. What stress happened at the 4 minute mark?

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• What stress happened at the 10 minute mark?

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• What stress happened at the 14 minute mark?

Practice Problems:

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• What stress happened at the 4 minute mark?

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Temperature increased; reaction shifts left

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• What stress happened at the 10 minute mark?

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[ CO ] decreased (was removed); reaction shifted left

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• What stress happened at the 14 minute mark?

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Volume increased; shift left

Practice Problems:

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• What stress happened at the 4 minute mark? Draw the rate vs time plot change at the 4 minute mark.

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• What stress happened at the 10 minute mark? Draw the rate vs time plot change at the 4 minute mark.

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• What stress happened at the 14 minute mark? Draw the rate vs time plot change at the 4 minute mark.

4 minute mark stress:

Increase in temperature

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10 minute mark stress:

CO was removed

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14 minute mark stress:

Volume was increased