Question

Explain how $C{ O }_{ 2 }$ is able to control fires.

Answer 1

Hint: Try to think about the gases which support a flame. And how does carbon dioxide cease gases supporting fire? Due to the heavier weight of carbon dioxide, it displaces other flame supporting gases.

Complete step by step answer: We know that carbon dioxide is used as a fire extinguisher. Fire burns in presence of flammable gases. And in the air, we have oxygen as the second most abundant element. So flame continues to burn in the presence of oxygen. When there is no oxygen present in surroundings of fire then the fire will stop burning. So many times during fire accidents we need to cut down oxygen supply for the fire to control it. Carbon dioxide has more atomic weight than oxygen gas. We know the phenomenon of diffusion of gases. The diffusion of a gas is inversely proportional to the square root of the molecular weight of the gas.
 So, oxygen diffuses more rapidly compared to carbon dioxide. Hence when we spray carbon dioxide gas on to fire it remains there for more time and it forms thick blankets around the fires and decreases the oxygen supply to the fire. Carbon dioxide also shows a cooling effect which helps in reducing temperature around fires rapidly. Because of the cooling effect of carbon dioxide, it is used as a coolant widely.

Note: Though there are many heavier gases they are not effective in controlling fires. Carbon dioxide shows a cooling effect and rapidly spreads over the fires. Though the diffusion principle is applicable for all gases other factors affect gases in the air.