I. Very Short Answer Type Questions
Question 1. What is the value of the gas constant in SI units?
Answer: 8.314 JK-1 mol-1.
Question 2. Define boiling point of a liquid.
The temperature at which the vapour pressure of a liquid is equal to external pressure is called boiling point of liquid.
Question 3. What is SI unit of
- (i) Viscosity
- (ii) Surface tension?
- (i) Unit of viscosity is Nsm-2
- (ii) Unit of surface tension is Nm-1
Question 4. What is the effect of temperature on
- (i) surface tension and
- (ii) Viscosity?
- (i) Surface tension decreases with increase of temperature.
- (ii) Viscosity decreases with increase of temperature.
Question 5. What is the unit of coefficient of viscosity?
Question 6. What do you understand by laminar flow of a liquid?
The type of flow in which there is regular gradation of velocity in passing from one layer to the next is called laminar flow.
Question 7. What do you mean by compressibility factor?
The deviation from ideal behaviour can be measured in terms of compressibility factor Z.
Question 8. What is Boyle Temperature?
The temperature at which a real gas obeys ideal gas law over an appreciable range of pressure, is called Boyle temperature or Boyle point.
Question 9. What is meant by elastic collision ?
Collision in which there is no loss of kinetic energy but there is transfer of energy, is called elastic collision.
Question 10. Define critical temperature of gas.
The temperature above which a gas cannot be liquefied.
Question 11. What are real gases ?
A gas which can deviate from ideal gas behaviour at higher pressure and lower temperature, is called a real gas.
Question 12. Define an ideal gas.
A gas that follows Boyle’s law, Charles’ law and Avogadro law strictly, is called an ideal gas.
Question 13. Name four properties of gases.
- Gases, have no definite shape and no definite volume.
- There is no force of attraction existing between the molecules of gases.
- Gases are highly compressible.
- Gases’can mix evenly and can spread in whole space.
Question 14. State Dalton’s law of partial pressure.
Daltons’ Law states that, total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases.
Question 15. What do you mean by aqueous tension?
Pressure exerted by saturated water vapour is called aqueous tension.
Question 16. Give mathematical expression for ideal gas equation.
PV = nRT
Where R is called Gas constant.
Question 17. Write van der Waals equation for n moles of a gas.
Where ‘a’ and ‘V are van der waals constants.
Question 18. How is compressibility factor expressed in terms of molar volume of the real gas and that of the ideal gas?
Question 19. Why liquids diffuse slowly as compared to gases?
In liquids, the molecules are more compact in comparison to gases.
Question 20. What is the effect of temperatures on the vapour pressure of a liquid?
Vapour pressure increases with rise in temperature.
Question 21. Why falling liquid drops are spherical?
Because of the property of surface tension, liquid tends to minimise its area.
II. Short Answer Type Questions
Question 1. A weather balloon has a volume of 175 dm3 when filled with hydrogen gas at a pressure of 1.0 bar. Calculate the volume of the balloon when it rises to a height where the atmospheric pressure is 0.8 bar. Assume that temperature is constant.
Question 2. A certain amount of a gas at 27°C and 1 bar pressure occupies a volume of 25 m3. If the pressure is kept constant and the temperature is raised to 77°C, what will be the volume of the gas?
From the available data: V1 = 25 m3, T1= 27 + 273 = 300 K
V2 = ? T2 = 77 + 273 = 350 K
Question 3. A flask was heated from 27°C to 227°C at constant pressure. Calculate the volume of the flask if 0.1 dm3 of air measured at 227°C was expelled from the flask.
Let the volume of the flask = V dm3 (after expelling the air)
V1 = V dm3, T1 = 27 + 273 = 300K
VT2 = (V + 0.1) dm3, T2 = 227 + 273 = 500 K
Question 4. A gas occupying a volume of 100 litres is at 20°C under a pressure of 2 bar. What temperature will it have when it is placed in an evacuated chamber of volume 175 litres? The pressure of the gas in the chamber is one-third of its initial pressure.
Question 5. At 25°C and 760 mm ofHg pressure a gas occupies 600 mL volume. What will be its pressure at a height where temperature is 10°C and volume of the gas is 640 mL?
Question 6. A 34.0 dm3 cylinder contains 212 g of oxygen gas at 21°C. What mass of oxygen must be released to reduce the pressure in the cylinder to 1.24 bar?
Question 7. The values of the van der Waal’s constants for a gas are a = 4.10 dm6 bar mol-2 and b = 0.035 dm3 bar mol-1. Calculate the values of the critical temperature and critical pressure for the gas.
Question 8. The pressure of a mixture of H2 and N2 in a container is 1200 torr. The partial pressure of nitrogen in the mixture is 300 torr. What is the ratio of H2 and N2 molecules in the mixture?
- (a) What do you mean by’Surface Tension’of a liquid?
- (b) Explain the factors which can affect the surface tension of a liquid.
(a) Surface tension: It is defined as the force acting per unit length perpendicular to the line drawn on the surface. It’s unit is Nnr1.
(b) Surface tension of a liquid depends upon following factors.
(i) Temperature: Surface tension decreases with rise in temperature. As the temperature of the liquid increases, the average kinetic energy of the molecules increases. Thus, there is a decrease in intermolecular force of attraction which decreases the surface tension.
(ii) Nature of the liquid: Greater the magnitude of intermolecular forces of attraction in the liquid, greater will be the value of surface tension.
Question 10. A neon-dioxygen mixture contains 70.6 g dioxygen and 167.5g neon. If pressure of the mixture of gases in the cylinder is 25 bar. What is the partial pressure of dioxygen and neon in the mixture?
III. Long Answer Type Questions
Question 1. State and explain Boyle’s law. Represent the law graphically.
It states that, the pressure of a fixed mass of a gas is inversely proportional to its ‘ volume if temperature is kept constant.
Question 2. Give an expression for the van der Wools equation. Give the significance of the constants used in the equation. What are their units?
When n is the no. of moles present and ‘a’ and ‘V are known as van der Waals constants.
Significance of van der Waals constants
van der Waals constant ‘a’ : ‘a’ is related to the magnitude of the attractive forces among the molecules of a particular gas. Greater the value of V, more will be the attractive forces.
Unit of ‘a’ = L2 mol-2
van der Waals Constant ‘b’: ‘b’ determines the volume occupied by the gas molecules which depends upon size of molecule.
Unit of ‘b’ = L mol-1.
Question 3. What are ideal and real gases? Out of CO2 and NH3 gases, which is expected to show more deviation from the ideal gas behaviour?
Ideal Gas: A gas that follows Boyle’s law, Charles’ law and Avogadro law strictly, is called an ideal gas. It is assumed that intermolecular forces are not present between the molecules of an ideal gas.
Real Gases: Gases which deviate from ideal gas behaviour are known as real gases. NH3 is expected to show more deviation. Since NH3 is polar in nature and it can be liquified easily.
Question 4. State and explain Dalton’s law of partial pressures. Can we apply Dalton’s law of partial pressures to a mixture of carbon monoxide and oxygen?
Dalton’s law of partial pressure: When two or more non-reacting gases are enclosed in a vessel, the total pressure of the gaseous mixture is equal to the sum of the partial pressures that each gas will exert when enclosed separately in the same vessel at constant temperature.
P= P1 + P2 + P3
Where, P is the total pressure of the three gases A, B, and C enclosed in a container. P1 , P2 and P3 are the partial pressures of the three gases when enclosed separately in the same vessel at a given temperature one by one.
No, the law cannot be applied. Carbon monoxide and oxygen readily combine to form carbon dioxide. The law can be applied only to the non-reacting gases.
IV. HOTS Questions
- (a) Why aerated water bottles kept under water during summer?
- (b) Which property of liquid is responsible for spherical shape of drop?
- (c) Why is moist air lighter than dry air?
- (d) Define aqueous tension.
- (e) What are units of a and b which are van der Waals constants?
- (a) To reduce temperature, so as to reduce pressure, otherwise bottle may burst.
- (b) Surface Tension.
- (c) Moist air has water vapours which lowers vapour density, so it is lighter.
- (d) It is pressure of water vapours at given temperature.
- (e) Unit of a is L2 mol-2, b is L mol-1.
Question 2. Why does sharpened edge becomes smooth on heating up to melting point?
On heating the glass, it melts and take up rounded shape at edges which has minimum surface area b/c of surface tension.
Question 3. Arrange the following in order of increasing density:
Question 4. An O2 cylinder has 10 LO2 at 200 atm. If patient takes 0.50 ml of O2 at 1 atm in one breath 37°C, how many breaths are possible?