Meaning of heat of displacement and Experiment: To determine the molar enthalpy change in the reaction between #Cu^(2+)# ions and zinc or iron
Answer Text: 4. Heat of displacement.- This refers to the enthalpy change that occurs when one mole of a substance is displaced from a solution of its ions.Experiment: To determine the molar enthalpy change in the reaction between #Cu^(2+)# ions and zincor iron.(i) Procedure:- A plastic cup or glass beaker is wrapped with a newspaper leaf.- 25 #cm^3# of 0.2M copper (II) sulphate solution is transferred into the beaker.- The steady temperature of the solution is noted.- 0.5g of zinc powder are carefully transferred into the plastic cup and stirred with a thermometer.- The highest temperature attained by the solution is recorded.Observations:- The blue colors of copper(II) sulphate fades.- Brown deposits of copper metal are formed in the plastic cup.Explanation:- Zinc is higher in the electrochemical series than copper;- Zinc therefore displaces copper ions from itssolution.#equation:Zn(s)+CuSO(aq) to ZnSO_4(aq) +Cu(s)Ionically:Zn(s)+Cu^(2+)(aq) to Zn^(2+)+ Cu(s)#- During the reaction the blue #Cu^(2+)# in the solution are replaced by the colorless #Zn^(2+)#.- Consequently the blue colour of the solution fades, as brown deposits of copper metal are formed in the plastic cup.- Excess solid (zinc powder) was used to ensure complete displacement of #Cu^(2+)#.Results:- Initial temperature of copper sulphate solution, #T_1# = 23˚C- Highest temperature of the mixture T2 = 33ºC- Temperature change, ΔT; = T2-T1 =10ºC- Volume of copper sulphate solution used = 25.0 #cm^3#.- Mass of zinc powder taken = 0.6g- Density of the solution = #1gcm^-3#.- Specific heat capacity of the solution = #4.2Kjkg^-1k^-1#.Assumptions:- The volume of the solution remains unchanged after thereaction. (Cu = 63.5, S = 32, O =16, Zn = 65, Fe =56)Question:Using the above data,calculate, calculate the;(i). Heat change for the above reaction.(ii). The molar heat of displacement of copper (II) ions.- Since the final temperature of the mixture is higher than initial temperature; it means the Hproducts is lower than Hreactants.- The reaction is thus exothermic.- Thus molar heat of displacement of #Cu^(2+) = - 210Kjmol^-1##Zn(s)+Cu^(2+)(aq) to Cu(s)+Zn^(2+)(aq), DeltaH=-210Kjmol^(-1)#Note:- The experimental value for the heat liberated in this reaction is lower than the theoretical value of #216Kjmol^-1#.Reasons:- The heat lost to the surroundings and the heat absorbed by the apparatus is not accounted for in thecalculations.- This reaction is typically a Redox reaction.