Question

Dry ice is used in fire extinguishers. The dry ice is stored in the cylinder in a solid form. When sprayed on a fire it quickly changes into the gas known as carbon dioxide $\left( \text{C}{{\text{O}}_{2}} \right)$. What is the change of state called?
(A) Sublimation
(B) Condensation
(C) Distillation
(D) Evaporation

Answer 1

Hint: The dry ice is a solid form of carbon dioxide. Carbon dioxide is a molecule in which a single carbon atom forms double bonds with two oxygen atoms $\left( \text{O}=\text{C}=\text{O} \right)$. This is non-flammable and colourless. When it is sprayed it gets converted into gaseous carbon dioxide. So, it means that solid is directly converted into the gaseous phase. Check out in which method, solid gets converted to gas.

Complete step by step solution:
Let us now discuss the options one-by-one to know the conversion of states behind every method:
A. Sublimation: Sublimation is a type of phase transition, in which solid substance gets directly converted into gaseous substance. Moreover, in this process, the substance does not pass through the liquid state. It is an endothermic process. When a gaseous substance gets converted into a solid substance, it is called de-sublimation or reverse of sublimation.
B. Condensation: It is a type of phase transition, in which gaseous substances are converted into liquid substances. In the water cycle, this process takes place. The process is initiated by gaseous volume forming the molecular clusters. When the liquid phase gets converted into a gaseous phase, it is called vaporization or reverse of condensation.
C. Distillation: The process of separation of components from a liquid mixture by condensation and boiling is called distillation. Distillation process works on the principle of differences in the relative volatility of the components. It is highly used in industrial processes.
D. Evaporation: This process is the same as that of vaporization, in this also liquid substances are converted into gaseous substances on the surface of the liquid. But it is a little different, in this method, liquid gets evaporated by transferring the energy of collision of liquid molecules to each other. When they have enough energy, the molecules escape in the air.

The change of state is called sublimation, which is option ‘A’.

Additional information:
Applications of dry ice are:
(1) It can be used to prevent and arrest the insects in closed containers as it completely displaces the oxygen gas, without altering the taste of the foods.
(2) It is mainly used for preserving the refrigerated foods when mechanical cooling is not available. The cold and frozen foods include ice creams and biological samples also.

Note: The states of matter are interconvertible. That is one form that can be changed into another form through a method. The liquid, gas and solid are the main three states of matter. The processes by which they can easily convert into each other are shown by the diagram: