Chemical Equilibrium in Solution: Le Chatelier's Principle PDF

Chemical equilibrium in solution Application of Le Chatelier’s principle  Purpose To apply Le Chatelier’s principle for a reversible reaction using different stress conditions for example(increase and decrease concentration of reactants and products) and temperature ...

Chemical equilibrium in solution Application of Le Chatelier’s principle  Purpose To apply Le Chatelier’s principle for a reversible reaction using different stress conditions for example(increase and decrease concentration of reactants and products) and temperature  Introduction Le Chatelier’s principle states that when a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress  Effect of concentration In an aqueous solution, iron (⫴) ions will react with thiocyanate ions Fe3+ + 6SCN- ⇋ [Fe(SCN)6]3- Blood red color An equilibrium is established among these ions, such equilibrium can be changed by decreasing or increasing the conc. of one of reactants and products in solution  Procedure Fe3+ + 6SCN- ⇋ [Fe(SCN)6]3- Blood red color Prepare 5 test tubes containing 4ml (Fe)3+ and 3 drops of (SCN)-: A- In tube 1 add 0.5ml of (SCN)- : ↑ SCN- will shift reaction forward so ↑ the red color B- In tube 2 add 0.5ml of NH4Cl: disappearance of blood red color , so reaction shifted backward due to formation of ferric chloride C- In tube 3 add 0.5ml of AgNO3: AgNO3 + SCN- ➞ ↓AgSCN (white ppt), so reaction shifted backward D- In tube 4 add 0.5ml of oxalic acid: disappearance of blood red color , so reaction shifted backward due to formation of ferric oxalate E- In tube 5 for control  Fe3+ + 6SCN- ⇋ [Fe(SCN)6]3- Test tube number 1 NH4SCN ➝ ↑ red color  Fe3+ + 6SCN- ⇋ [Fe(SCN)6]3- Test tube (2): Test tube (3): Test tube (4): NH4Cl ➝ ↓ red AgNO3 ➝ ↓ red Oxalic acid ➝ ↓ color due to the color + ⤓ white red color due to formation of ppt. of silver the formation of ferric chloride thiocyanate ferric oxalate  Effect of temperature since reaction is exothermic (Δ H= -ve) Fe3+ + 6SCN- ⇋ [Fe(SCN)6]3- + heat A- Put one tube in hot water Reaction is shifted to backward Red color is faded (reaction is shifted to cold direction) B- Put one tube in ice Reaction is shifted to forward Red color become more intense (reaction is shifted to hot direction)