A person living in Shimla observed that cooking food without using a pressure cooker takes more time. The reason for this observation is that at high altitude:

Question

Philoid · Accepted Answer

There are 2 conditions for liquefaction of gases:

• Low temperature

• High pressure

LOW TEMPERATURE: As the temperature of a gas is low, the kinetic energy of the molecule also decreases, which leads volume to get decrease. As the temperature decreases, molecules come close to each other and changes into a liquid.

HIGH PRESSURE: As the pressure increases, makes gas molecule come close to each other and convert into liquid. For each gas, there is a specific temperature above which gas never be liquefied, however, high pressure is applied.

Therefore the effect of temperature is more important than that of pressure.

The atmospheric pressure is very low at high altitudes, so at very low temperatures, vapour pressure of the liquid becomes equal to atmospheric pressure i.e. below boiling point. Liquid starts to boil much before the food is cooked. To avoid this situation, we use pressure cookers. Pressure cooker raises the pressure so that the boiling point of liquid increases. This helps in efficient cooking of food in a short time.