Question

Part A

A calorimeter contains 35.0 mL of water at 11.0 ∘C . When 1.30 g of X (a substance with a molar mass of 46.0 g/mol ) is added, it dissolves via the reaction

X(s)+H2O(l)→X(aq)

and the temperature of the solution increases to 29.0 ∘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

1.30 g of X (a substance with a molar mass of 46.0 g/mol ) is added.

The number of moles of X added.

The enthalpy change for the reaction

The specific heat of the solution is 4.18 J/ (g deg C)

The enthalpy change for the reaction

This is the enthalpy change for the dissolution of 0.02826 moles of X. For 1 mole of X, the enthalpy change is

Convert the unit from J to kJ

The answer to three significant figures is

Part B

10.0 g of sucrose (molecular weight 342 g/mol)

The heat capacity is 7.50 kJ/ deg C. The temperature increase is 22.0 deg C.

The change in internal energy for 0.02924 moles of sucrose combustion is

The change in internal energy for 1 mole of sucrose combustion is

To three significant figures, the answer is