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 ?
a)
A body with large reflectivity is a poor emitter of heat because large reflectivity makes the body a poor absorber of heat radiations and hence, a poor emitter of radiations.
Thus, a body with a large reflectivity is a poor emitter.
b)
Since, brass is a good conductor of heat therefore, when someone touches the brash tumbler, heat is conducted from human body to the tumbler easily. So, the temperature of the human body reduces to a lower value and consequently tumbler appears colder.
Since, wood is a insulator of heat therefore, when someone touches the wooden tray, heat does not flow from human body to the tray. So, the temperature of the body does not reduces and it appear comparably hotter.
c)
An optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.
According to black body radiation equation
E = σ ( T 4 − T 0 4 )
Where, E is the energy radiation from a black body, T is the temperature of optical
Pyrometer and T 0 is the temperature of open space.
An increase in temperature of open space reduces the radiation energy.
When the same piece of iron is placed in a furnace, the radiation energy is given as
E = σ T 4
Thus, the optical pyrometer gives the correct reading inside the furnace but not in the open.
d)
The earth without its atmosphere would be inhospitably cold because in the absence of atmospheric gases no extra heat will be trapped. All the heat received from the sun would be radiated back from earth’s surface to the space.
e)
Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water because steam contains extra heat in the form of latent heat. Thus, when the exchange of heat takes place between the cooler building and the hot steam, it can supply more heat by condensing to liquid water state therefore, proving to be more efficient in warming the building.
a)
A body with large reflectivity is a poor emitter of heat because large reflectivity makes the body a poor absorber of heat radiations and hence, a poor emitter of radiations.
Thus, a body with a large reflectivity is a poor emitter.
b)
Since, brass is a good conductor of heat therefore, when someone touches the brash tumbler, heat is conducted from human body to the tumbler easily. So, the temperature of the human body reduces to a lower value and consequently tumbler appears colder.
Since, wood is a insulator of heat therefore, when someone touches the wooden tray, heat does not flow from human body to the tray. So, the temperature of the body does not reduces and it appear comparably hotter.
c)
An optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.
According to black body radiation equation
Where,
Pyrometer and
An increase in temperature of open space reduces the radiation energy.
When the same piece of iron is placed in a furnace, the radiation energy is given as
Thus, the optical pyrometer gives the correct reading inside the furnace but not in the open.
d)
The earth without its atmosphere would be inhospitably cold because in the absence of atmospheric gases no extra heat will be trapped. All the heat received from the sun would be radiated back from earth’s surface to the space.
e)
Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water because steam contains extra heat in the form of latent heat. Thus, when the exchange of heat takes place between the cooler building and the hot steam, it can supply more heat by condensing to liquid water state therefore, proving to be more efficient in warming the building.
