IMAT 2012 Q72 [Paraffin Wax]

At the melting point, which of the following are correct about paraffin wax?

  1. The substance becomes more disordered.
  2. The wax takes in heat but its temperature stays the same.
  3. Bonds between the carbon and hydrogen atoms are broken.

A. 1, 2 and 3
B. 2 and 3 only
C. 2 only
D. 1 and 3 only
E. 1 and 2 only

For 1, we know that entropy, the disorder of particles of a substance, increases when the amount of motion within a system increases. Since we are supplying the Paraffin with heat, the kinetic energy increases. Therefore making this statement true.

For 2, we also know that in changes of state (melting, boiling, freezing, etc.) the temperature does not change, increasing nor decreasing. Instead, the energy is used to break intermolecular bonds. Hence making this statement true.

For 3, the only bonds that break when melting are the intermolecular bonds of the paraffin (Van der Waal forces)- the carbon-hydrogen bonds remain. And so this statement is false.

Our answer should be 1 and 2 only, option E.