Question

Why kerosene doesn't catch fire as petrol does. Explain

Answer 1

Hint: Kerosene and petrol are widely used as fuels or a component of fuel. These are chemically hydrocarbons. In this context,we need to consider their boiling points,vapour pressure,flash point and auto ignition temperature which would give a brief idea to answer this question.Some properties of kerosene makes it a safe fuel to handle and store as well when compared to petrol.

Complete answer:
Let us first understand the terms mentioned in the hint. Boiling point is the temperature at which a liquid turns into vapour state. Vapour pressure of any liquid is said as the pressure exerted by a vapour which is present above the liquid at equilibrium. Flash point is that temperature where flammable vapours are generated at the surface .Auto ignition is the temperature where a substance starts igniting spontaneously. For petrol the auto ignition temperature,vapour pressure and boiling point is low which makes it catch fire more easily than kerosene and hence it's more volatile. Hence, petrol ignites at a faster rate when compared to kerosene. Ignition is nothing but the process of burning. Hope you have understood the chemistry behind it.

Note:
Kerosene is actually extracted from petrol through a fractional distillation process. The principle in this process is that when two liquids are heated ,the one with low boiling point starts boiling and evaporates each fraction and gets condensed separately. This is the most important process in oil refining industries where liquids with different boiling points are extracted and then collected.