Question

Part A

A calorimeter contains 16.0 mL of water at 12.5 ∘C . When 1.70 g of X (a substance with a molar mass of 54.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 30.0 ∘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. Hints ΔH = kJ/mol SubmitMy AnswersGive Up

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

no of mol of x dissolved = 1.7/54 = 0.0315 mol

mass of mixer = 16+1.7 = 17.7 g

specific heat of solution (s) = 4.184 j/g.c

DT = 30-12.5 = 17.5 C

heat liberated(q) = m*s*DT

                   = 17.7*4.184*17.5

                   = 1296 joule

DHdiss = -q/n

        = -1.296/0.0315

        = - 41.1 kj/mol

part B

no of mol of sucrose burned = 10/342 = 0.02924 mol

heat released(q) = C*DT

                  = 7.5*22

                  = 165 kj

DHcomb = -q/n

        = -165/0.02924

        = -5.64*10^3 kj/mol