Q12.29P - Chemistry: Molecular Nature Of Matter And Change

Question

Use the Figure to answer the following: 

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a) Carbon dioxide is sold in steel cylinders under pressures of approximately 20atm. Is there liquid  ${\mathbf{CO}}_{\mathbf{2}}$ in the cylinder at room temperature ($\mathbf{~}{\mathbf{20}}^o\mathbf{C}$ )? At ${\mathbf{40}}^o\mathbf{C}$?At$\mathbf{-}{\mathbf{40}}^o\mathbf{C}$  ? At $\mathbf{-}{\mathbf{120}}^o\mathbf{C}$ ? 

b) Carbon dioxide is also sold as solid chunks, called dry ice, in insulated containers. If the chunks are warmed by leaving them in an open container at room temperature, will they melt? 

c) If a container is nearly filled with dry ice and then sealed and warmed to room temperature, will the dry ice melt? 

d) If dry ice is compressed at a temperature below its triple point, will it melt?                 

 

Step-by-Step Solution

Answer

(a) The  will exists in a gas state at  $~{20}^{o}C$and  ${40}^{o}C$ temperature at 20 atm and the$C{O}_2$  exist as a liquid state $-{40}^{o}C$at  and the$C{O}_2$  exist as a solid-state at  $-{120}^{o}C$.

(b) The dry ice solid is converted into the gas phase after sublimation $C{O}_2$  (s) into$C{O}_2$   (g).

(c) Yes, the dry ice will melt but because of the lack of oxygen in a closed container, it will convert into carbon monoxide.

(d) The dry ice will start melting as soon as it reaches the triple point.

Step 1: Enthalpy of Vaporization

The phase diagram is the diagram which shows the change in phase. It tells about the change into all phases – Solid, Liquid and Gaseous.

It represents all the phases and transition are shown by the lines and the area between lines show the whole phase of the molecule.

 

The critical point can be explained as the point where the density of the different phases becomes equal. The critical point in which the volume of the two phases are the same at certain pressure and temperature.

 

The point can be said as the ‘Triple Point’ where  all the three phases are in equilibrium and the phases co-exist with each other.

 

Step 2: Phases of Carbon dioxide

From the graph, the${\mathbf{CO}}_2$ will exist in a gas state at$\mathbf{~}{\mathbf{20}}^o\mathbf{C}$  and  ${\mathbf{40}}^o\mathbf{C}$temperature at 20atm and the${\mathbf{CO}}_2$  exist as a liquid state at $\mathbf{-}{\mathbf{40}}^o\mathbf{C}$ and the ${\mathbf{CO}}_2$ exist as a solid-state at  $\mathbf{-}{\mathbf{120}}^o\mathbf{C}$. The molecule also exists in three phases at different temperatures. At temperature near room temperature, it exists as a gaseous state whereas as temperature goes lesser the molecule started bonding and the molecule converts into a liquid state and changes into a strong bond in the solid phase.

 

Step 3: Sublimation Process

The dry ice solid is converted into the gas phase after sublimation ${\mathbf{CO}}_2$  (s) into ${\mathbf{CO}}_2$  (g). The dry ice is warmed by leaving them in an open container and it melts into gas as a dry fog.

 

Step 4: Conversion into poisonous gas

If the dry ice is melted into gas in a closed container it will start melting into gas but due to the lack of oxygen, it will convert into carbon monoxide which is a poisonous gas. The lack of oxygen in the melting of ${\mathbf{CO}}_2$  (s) into  ${\mathbf{CO}}_2$ (g) will lead to CO.

 

Step 5: Triple Point Explanation

The dry ice will start melting after the triple point is reached. As the gas is compressed by applying the pressure on it so the pressure is increased but at a temperature lower than triple point it will start melting and exert pressure as the temperature increases.