Question

Part A A calorimeter contains 21.0 mL of water at 11.0 ∘C . When 1.60 g of X (a substance with a molar mass of 72.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 26.0 ∘C . Calculate the enthalpy change, ΔH, for this reaction per mole of X. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g⋅∘C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures. part b Consider the reaction C12H22O11(s)+12O2(g)→12CO2(g)+11H2O(l) in which 10.0 g of sucrose, C12H22O11, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/∘C. The temperature increase inside the calorimeter was found to be 22.0 ∘C. Calculate the change in internal energy, ΔE, for this reaction per mole of sucrose. Express the change in internal energy in kilojoules per mole to three significant figures.

Answer 1

PART A

mass of the mixture = v*d+mass of X

= 21.0*1+1.6 = 22.6 g

s = specific heat of mixture = 4.184 j/g.c

DT = 26-11 = 15c

heat released(q) = m*s*DT

     = 22.6*4.184*15

     = 1.418 kj

no of mol of X = w/mwt = 1.6/72 = 0.022 mol

DHrxn = -q/n

       = -1.418/0.022

       = -64.4 kj/mol

part B

heat released during combustion reaction(q) = C*DT

    = 7.5*22

     = 165 kj

No of mol of sucrose burned = w/mwt = 10/342.3 = 0.0292 mol

DUrxn = -q/n = -165/0.0292 = -5650.7 kj/mol

           answer: -5.65*10^3 kj/mol