(Calcutta University) BSc (Chemistry) II Practice questions

Chemistry Gen: Course Description Year 2 [PART II]

Practice questions

 Unit I. Basic physical chemistry I

1. When you place ice cubes on the table on a hot summer day, they melt and the liquid water then evaporates. What happens to dry ice (solid carbon dioxide) if it is left on the table? (2)
2. Explain using kinetic molecular theory, why pressure exerted by gases is in all directions? (2)
3. A sample of nitrogen gas has a volume of 10L at 101.3kPa and 20⁰C. To preserve biological tissue, the nitrogen gas is cooled to -190⁰C, almost the temperature of liquid nitrogen, at a pressure of 101.3kPa. What volume will the nitrogen occupy at this temperature? (2)
4. A stone is dropped from the top of a cliff and is found to travel 44.1m diving the last second before it reaches the ground. What is the height of the cliff? g = 9.8m/s² (2)
5. If an 8g sample of a gas occupies 12.3L at 400 torr, what volume will the gas occupy at the same temperature and 600 torr? (2)
6. If a 9.3g sample of a gas occupies 12.3 L at 750 torr and 450K, what volume will the gas occupy at the same pressure and 25⁰C? (2)
7. Evaluate R if 1 mole of an ideal gas occupies 22.4L at 1 atm and 0⁰C. (2)
8. A 40L sample of N2 is collected over water at 220C and an atmospheric pressure of 727 torr. Calculate the volume that the dry N2 will occupy at 1 atm and 0⁰C. The vapor pressure of water is 20 torr at 22⁰C. (2)
9. A 1 mole sample of argon exerts a pressure of 64.2 atm in a 0.25 L container at 223K. Calculate the pressure, P_ideal assuming ideal gas behavior. (2)
10. Why is the molar heat capacity of molecular hydrogen not [7/2 R] at all temperatures? (2)
11. Why classical mechanics fails and quantum mechanics succeeds in correctly predicting the observed heat capacities of gases. (2)
12. Why is ice less dense than liquid water while H₂S (s) is more dense than H₂S (l)? (3)
13. Why does water have a high specific heat? (2)
14. A vessel is filled with gas at some equilibrium pressure and temperature. Can all gas molecules in the vessel have the same speed? (2)
15. An ideal gas is contained in a vessel at 300K. If the temperature is increased to 900K, by what factor does each one of the following change? (a) the average kinetic energy of the molecules. (b) the rms molecular speed. (c) the average momentum change of one molecule in a collision with a wall. (d) the rate of collisions of molecules with walls. (e) the pressure of the gas. (5)