Pressure cooker reduces cooking time? What is the Science behind it?
According to the law of mass action, the quantitative effects of temperature, pressure, concentration, volume and other factors on the equilibrium of a chemical reaction can be studied. For the qualitative study of these factors on equilibrium, franchise science le chatelier introduced a generalized rule in 1884 called le chatelier’s Principle.
French chemist Henry Louis Le Chatelier,
According to this rule –
If a system in equilibrium is subjected to a charge of concentration, pressure, temperature, volume etc., the equilibrium shifts in the direction that tends to undo the effect of the change.
Vaporisation of water:
Heat is exploited in the evaporation of water and the volume increases.
The effect of change in heat and pressure on this equilibrium can be known on the basis of le chatelier’s law –
Water ⇋ water vapour — 540 cal/gram
Effect of heat: Due to the increase of heat, equilibrium is displaced towards which the heat is absorbed. Therefore, the speed of evaporation of water also increases with the increase of heat.
Pressure effect: There is a decrease in pressure in the opposite direction of the above equilibrium. Therefore, due to the increase in pressure, the equilibrium will be displaced in the opposite direction, that is, the evaporation of water will decrease. Therefore increase in pressure increases the boiling point of water. Pressure cooker increases the boiling point of water when cooking lentils, more heat is available to melt the lentils and the lentils cook quickly.
Read more about Le chatalier’s principle