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physics ncert solutions class 11th Physics Class 11th Thermal Properties of Matter

11.21 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 15 °C under 56 atm ?

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Payal Gupta | Contributor-Level 10

4 months ago

11.21

(a) The P-T phase diagram for CO₂is shown here. O is the triple point of the CO₂phase diagram. This means that at the temperature and pressure corresponding to this point, the solid, liquid and vaporous phases of CO₂exists in equilibrium.

(b) The fusion and the boiling points of CO₂decreases with a decrease in pressure.

(c) The critical temperature and critical pressure of CO₂ are 31 $?$ 72.9 atm respectively. Even if it is compressed to a pressure greater than 72.9 atm, CO₂ will not liquefy above the critical temperature.

(d) It can be concluded from the P-T phase diagram of CO2 that:

CO₂ is gaseous at -70 $?$ , under 1 atm pr

...more

11.21

(b) The fusion and the boiling points of CO₂decreases with a decrease in pressure.

(d) It can be concluded from the P-T phase diagram of CO2 that:

CO₂ is gaseous at -70 $?$ , under 1 atm pressure.

CO₂ is solid at -60 $?$ , under 10 atm pressure.

CO2 is liquid at 15 $?$ , under 56 atm pressure.

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A glass full of hot milk is poured on the table. It begins to cool gradually. Which of the following is correct?

(a) The rate of cooling is constant till milk attains the temperature of the surrounding

(b) The temperature of milk falls off exponentially with time

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This is a multiple choice answer as classified in NCERT Exemplar

(b), (c), (d) When the hot milk in the table is transferred to the surroundings by conduction, convection and radiation.

According to newton's law of cooling temperature of the milk falls of exponentially. Heat also will be transferred from surroundings to the milk but will be lesser than that of transferred from milk to surroundings. So option b, c, d satisfy.

Refer to the plot of temperature versus time (Fig) showing the changes in the state of ice on heating (not to scale) Which of the following is correct?

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This is a multiple choice answer as classified in NCERT Exemplar

(a), (d) During the process AB temperature of the system is 0⁰C . hence it represents phase change that is transformation of ice into water while temperature remains 0⁰C.

BC represents rise in temperature of water from 0⁰C to 100⁰C. now water starts converting into steam which is represented by CD.

Which is only represents by a, d options

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