a)A calorimeter contains 22.0 mL of water at 14.5 C . When 1.80 g of X (a substa

Question

a)A calorimeter contains 22.0 mL of water at 14.5 C . When 1.80 g of X (a substance with a molar mass of 50.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 27.0 C . Calculate the enthalpy change, H, 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/(gC)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings.

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, E, for this reaction per mole of sucrose.

Express the change in internal energy in kilojoules per mole to three significant figures.

Explanation / Answer

a) we need to conserve the energy to get the results.so,
since the specific heat of the solution is same as that of water,
dEnergy = -(22+1.8)*4.18*(27-14.5)
=-1243.55 Joules
so dH= energy/moles
= -1.24355*(50/1.8)
=-34.54 kJ/mol

b)burning point of sucros = 186 C
heat capacity of sucrose = 0.3*4.18
energy change = 0.3*4.18*10*(186-22) + 7.5*1000*(186-22)
=1232.06 kJ
so the change in internal energy per moles =1232.06*(342.2/10)
=42161.1 kJ/mol

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