Q16 of 26 Page 294

Answer the following questions based on the P-T phase diagram of carbon dioxide:

(a) At what temperature and pressure can the solid, liquid and vapour phases of CO2 co-exist in equilibrium?


(b) What is the effect of decrease of pressure on the fusion and boiling point of


CO2?


(c) What are the critical temperature and pressure for CO2? What is their significance?


(d) Is CO2 solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60 °C under 10 atm, (c) 15 °C under 56 atm?

The P-T phase diagram of CO2 is as follows:


(a) The solid, liquid and vapour phase of carbon dioxide exist in equilibrium at the triple point, i.e., the point corresponding to the temperature value of - 56.7° C and pressure value of 5.1 atm.


(b) With the decrease in pressure, both the fusion and boiling point of carbon dioxide will decrease.


(c) For carbon dioxide, the critical temperature is 31°C and critical pressure is 72.9 atm. If the temperature of carbon dioxide is more than 31° C, it cannot be liquified irrespective of the applied pressure.


(d) Carbon dioxide will be a vapour at 70°C under 1 atm, a solid at -6°C under 10 atm and a liquid at 15°C under 56 atm.


More from this chapter

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14

In an experiment on the specific heat of a metal, a 0.20 kg block of the metal at 150 °C is dropped in a copper calorimeter (of water equivalent 0.025 kg) containing 150 cm3 of water at 27 °C. The final temperature is 40 °C. Compute the specific heat of the metal. If heat losses to the surroundings are not negligible, is your answer greater or smaller than the actual value for specific heat of the metal?

 15

Given below are observations on molar specific heats at room temperature of some common gases.































Gas



Molar specific heat (Cv) (cal mo1–1 K–1)



Hydrogen



4.87



Nitrogen



4.97



Oxygen



5.02



Nitric oxide



4.99



Carbon monoxide



5.01



Chlorine



6.17



The measured molar specific heats of these gases are markedly different from those for monatomic gases. Typically, molar specific heat of a monatomic gas is 2.92 cal/mol K. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine?

 17

Answer the following questions based on the P – T phase diagram of CO2:

(a) CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally.


Does it go through a liquid phase?


(b) What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure?


(c) Describe qualitatively the changes in a given mass of solid CO2 at 10 atm pressure and temperature –65 °C as it is heated up to room temperature at constant pressure.


(d) CO2 is heated to a temperature 70°C and compressed isothermally. What changes in its properties do you expect to observe?

 18

A child running a temperature of 101°F is given an antipyrin (i.e. a medicine that lowers fever) which causes an increase in the rate of evaporation of sweat from his body. If the fever is brought down to 98 °F in 20 min, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is 30 kg. The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about 580 cal g–1.