Question

Paraffin wax contracts on solidification. So change in melting point with pressure
A) Increases
 B) Decreases
 C) Remain the same.
D) We can’t say.

Answer 1

Hint: Solidification of a substance is the process of changing its state from liquid to solid. Usually the substances contract during freezing. In a solid substance, atoms are more closely arranged than in a liquid. Hence, more energy is needed to break the force between the atoms.

Complete answer:
The change of state of a substance from liquid to solid is called solidification of casting or freezing. A pure substance freezes at a temperature that is equal to its melting point. In most of the substances, freezing causes contraction and melting causes expansion. We know that all substances are made up of tiny particles, which are always moving. The distance between them is different in gas, liquid and gaseous forms. When a substance expands or contracts, the space between the particles that change, but particle size remains the same. Freezing a substance will cause its particles to closely arrange, hence its volume reduces. While melting, its volume increases, because liquids take up more space than solids. And if you increase the pressure, it becomes harder to change into a state that needs more volume. So, more energy is needed, thus temperature, to melt. Hence, the melting point of paraffin wax is increased with pressure.

Therefore, the answer is option A.

Note:
Abnormal solids, like bismuth and ice contract on melting into liquids. Water freezes to ice cause expansion and ice melt to water causes contraction. The density of water is the highest at 4 °C. At this temperature, water reaches its minimum volume. This is why ice floats on water.