Question

Some building materials contain small capsules filled with paraffin wax to improve the insulating properties of the materials. The melting and freezing of paraffin inside the capsules in the material helps to regulate temperature. Paraffin wax begins to melt at 37°C37°C.(a) While the wax is melting, is the net flow of thermal energy from the wax to the surroundings or from the surroundings to the wax? Justify your answer.(b) Calculate the amount of thermal energy, in kJkJ, that is required to melt 15.215.2 grams of solid paraffin wax when the temperature of the surroundings is above the melting point of paraffin. (The molar mass of paraffin is 282.62g/mol282.62g/mol, and its molar heat of fusion is 48.78kJ/mol)(c) When paraffin wax melts, its density decreases. Provide a particle-level explanation of this observation.

Answer 1

Answer:

(a)

From surrounding to wax

(b)

Q = 2.62 KJ

(c)

Density of a substance is defined as the no. of particles of the substance, that occur in a unit volume. So, when the substance melts, the inter-molecular attractive forces and bonds between molecules or atoms are weakened. This, increases the distance between the molecules or atoms. Hence, the no. of particles in a unit volume is decreased. As, a result of this, the density of the substance also decreases.

Explanation:

(a)

During the melting process, the solid material or substance requires energy, in order to break the bonds between its molecules or atoms.

Therefore, while the wax is melting, the net flow of thermal energy is from surrounding to the wax.

(b)

The amount of energy required to melt solid paraffin wax is given by the formula:

Q = nC

where,

Q = amount of energy

C = Molar Heat of Fusion = 48.78 KJ/mol

n = No. of Moles = Mass in gram/Molar Mass = (15.2 g)/(282.62 g/mol)

n = 0.0538 mol

Therefore,

Q = (0.0538 mol)(48.78 KJ/mol)

Q = 2.62 KJ

(c)

Density of a substance is defined as the no. of particles of the substance, that occur in a unit volume. So, when the substance melts, the inter-molecular attractive forces and bonds between molecules or atoms are weakened. This, increases the distance between the molecules or atoms. Hence, the no. of particles in a unit volume is decreased. As, a result of this, the density of the substance also decreases.