Increasing the concentration of a substance in a reversible reaction shifts the equilibrium to decrease the concentration of that substance. For example, adding more water to a reaction producing bismuth oxychloride and hydrochloric acid from bismuth chloride and water would shift the equilibrium right, producing more products. Similarly, adding more chlorine gas to a reaction producing iodine trichloride from chlorine and iodine chloride would make the mixture appear more yellow by shifting the equilibrium to the right.

1. Concentration and equilibrium

2. Concentration and equilibrium
Changing the concentration of a substance affects the
equilibrium of reversible reactions involving solutions.
increasing the equilibrium shifts to
concentration of = decrease the amount of
substance A substance A

3. Concentration and equilibrium
Changing the concentration of a substance affects the
equilibrium of reversible reactions involving solutions.
increasing the equilibrium shifts to
concentration of = decrease the amount of
substance A substance A
decreasing the equilibrium shifts to
concentration of = increase the amount of
substance A substance A

4. Opposing changes in concentration (1)
Bismuth chloride reacts with water to produce a white
precipitate of bismuth oxychloride and hydrochloric acid.

5. Opposing changes in concentration (1)
Bismuth chloride reacts with water to produce a white
precipitate of bismuth oxychloride and hydrochloric acid.
bismuth bismuth hydrochloric
chloride
+ water oxychloride
+ acid
BiCl3 (aq) + H2O (l) BiOCl (s) + 2HCl (aq)

6. Opposing changes in concentration (1)
Bismuth chloride reacts with water to produce a white
precipitate of bismuth oxychloride and hydrochloric acid.
bismuth bismuth hydrochloric
chloride
+ water oxychloride
+ acid
BiCl3 (aq) + H2O (l) BiOCl (s) + 2HCl (aq)
What will happen if more H2O is added?

7. Opposing changes in concentration (1)
Bismuth chloride reacts with water to produce a white
precipitate of bismuth oxychloride and hydrochloric acid.
bismuth bismuth hydrochloric
chloride
+ water oxychloride
+ acid
BiCl3 (aq) + H2O (l) BiOCl (s) + 2HCl (aq)
What will happen if more H2O is added?
 The equilibrium will shift to decrease the amount of
water, i.e. to the right.
 More BiOCl and HCl will be produced.

8. Opposing changes in concentration (1)
Bismuth chloride reacts with water to produce a white
precipitate of bismuth oxychloride and hydrochloric acid.
bismuth bismuth hydrochloric
chloride
+ water oxychloride
+ acid
BiCl3 (aq) + H2O (l) BiOCl (s) + 2HCl (aq)
What will happen if more H2O is added?
 The equilibrium will shift to decrease the amount of
water, i.e. to the right.
 More BiOCl and HCl will be produced.
If H2O is removed, more BiCl3 and H2O will be produced.

9. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.

10. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)

11. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)
pale green brown yellow

12. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)
pale green brown yellow
What effect will adding more Cl2
have on the colour of the mixture?

13. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)
pale green brown yellow
What effect will adding more Cl2 It will become
have on the colour of the mixture? more yellow.

14. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)
pale green brown yellow
What effect will adding more Cl2 It will become
have on the colour of the mixture? more yellow.
What effect will removing Cl2
have on the colour of the mixture?

15. Opposing changes in concentration (2)
Chlorine gas reacts with iodine chloride to produce
iodine trichloride.
iodine iodine
chlorine + chloride trichloride
Cl2 (g) + ICl (l) ICl3 (s)
pale green brown yellow
What effect will adding more Cl2 It will become
have on the colour of the mixture? more yellow.
What effect will removing Cl2 It will become
have on the colour of the mixture? more brown.