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

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

Demonstration The chemical equation for the reaction was Co(H2O)62+ + 4Cl - CoCl42- (aq) + 6H2O 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!

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

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

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

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’

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

Comments Most chemical reactions of biochemical systems are at equilibrium