Afew pieces of dry ice, co2(s), at -78°c are placed in a flask that contains air at 21°c. the flask is sealed by placing an uninflated balloon over the mouth of the flask. as the balloon inflates, the dry ice disappears and no liquid is observed in the flask.

80 state the direction of heat flow that occurs between the dry ice and the air in the flask.
81 write the name of the process that occurs as the dry ice undergoes a phase change in the flask. [1]
82 compare the entropy of the co2 molecules in the dry ice to the entropy of the co2 molecules in the inflated balloon.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.