1. Solution Equilibrium A pink solution is warmed and becomes blue
Upon cooling it becomes pink again,
demonstrating a reversible chemical change

2. Purpose To shift a chemical equilibrium by temperature alone
To observe the color change which occurs and relate it to the chemical reaction for the demonstration

3. Demonstration The chemical equation for the reaction was
Co(H2O) Cl CoCl42- (aq) H2O
Higher temperatures shift the equilibrium to the blue
CoCl42- specie
Lower temperatures favor the pink
Co(H2O)62+ specie
Thus, the reaction adjusted to its environment!

4. Concepts 1. Reversible Chemical Reactions 2. Chemical Equilibria
3. Hydrated Ions

5. 1. Reversible Chemical Reactions
Not all chemical reactions convert reactants completely to products
A + B C + D
Many reactions will contain ALL species rather than converting completely
The double arrow indicates the reaction is reversible and both A and B as well as C and D are simultaneously present when the reaction is finished

6. 2. Chemical Equilibrium In a reversible chemical reaction A + B C + D
reactants are said to be
“in equilibrium” with their products
Equilibria may lie
more toward products
A + B C + D or
more toward reactants

7. 3. Hydrated Ions
Ions in aqueous solution are surrounded by a shell of water
Such ions are said to be hydrated
Hydrated ions such as sodium ion are written as Na+(aq) where aq is Latin for aqua, meaning ‘water’

8. Conclusions
The equilibrium of a solution at a given temperature shifted when the temperature was changed
The change was noted by the color change from the pink, hydrated ion to the blue, anhydrous ion
The change was reversible

9. Comments Most chemical reactions of biochemical systems are at
equilibrium