CHAPTER-18
Behaviour of Gases
Text Book Question and Answers
I. Answer the following
1. Define Charles law.
“At constant pressure, the volume of a fixed mass of a gas is directly proportional to its absolute temperature”– This is Charles law.
2. Caution “store in cool and dry place” is printed on medicine bottles. Why?
When the bottle is exposed, due to heat, it expands as the gas inside the bottle expands as temperature rises. To increase the volume the bottle explodes.
3. Define Boyle’s law.
“At constant temperature, the volume of a given mass of dry gas is inversely proportional to its pressure” – This is Boyles law.
4. What do you mean by Diffusion?
Random movement of gaseous molecules from the region of higher concentration to the region of lower concentration is called diffusion.
5. Define rate of diffusion?
The volume of gas diffusing per unit time is called rate of diffusion.
6. What is the relation between diffusion and mass?
The rate of diffusion is inversely proportional to square root of mass
r = K
Where m = mass, r = rate of diffusion, v = volume.
7. The volume of the gas found to be at a pressure of 2500 Pa. when the pressure was decreased by 500 Pa the gas occupied a volume of 2400 litres. Calculate the initial volume occupied by gas before the change was done at constant temperature?
Data:
P_{1} = 2500,
P_{2} = 2500-500 = 2000
V_{2} = 2400
V_{1} =?
Solution:
According to Boyle’s law
P_{1} V_{1 }= P_{2} V_{2} (at constant temperature)
2500 x V_{1} = 2000 x 2400
V_{1} = 1920 litres
8. About 6 litres of oxygen gas is collected at 300K. If for a particular use, the volume has to be reduced to 1/3 of its original volume, find the gas has to be cooled? (pressure is kept constant)
Data:
V_{1} = 6 litre
V_{2} = 1/3 x 6 = 2 litre
T_{1} = 300K,
T_{2} =?
Solution:
According to Charles law (at constant pressure)
V_{1}/T_{1} = V_{2}/T_{2}
6/300 = 2/ T_{2}
T_{2} = 100K.
The gas has to be cooled to 100k,
II. For each of the following statements or questions four alternatives are given. Choose the most appropriate alternative:
1. The expression which do not says relation between volume and temperature at constant temperature is -------
a. V = KT b. T = KV c. V/T = K d. V = K/T
2. The temperature which is also called Absolute zero is ------
a.0^{0}C b. 0^{0}F c. -273 ^{0}C d. -273 ^{0}K
3. The expression for relation between volume and pressure at constant temperature is
a. P/V = K b. T = PV c. V/ P = K d. PV = K
III. Fill in the blanks with right answer
1. Under constant pressure , per degree rise in temperature , the volume of gas is increased by ------- of the original volume at 0^{0}C. ( 1 / 273)
2. The S.I unit of temperature is --------- (kelvin)
3. The volume of gas diffusing per unit time is --------- ( rate of diffusion )
IV. Match the followings
A | B | C |
1.Charle’s law | i)Volume of gas diffused / Time(3) | a) TV= PK |
2. Boyle’s law | ii) constant volume | b) V = KT (1) |
3. Rate of diffusion | iii) constant temperature (2) | c) PV = K (2) |
| iv) Constant pressure (1) | d) r = k √v / √m (3) |
Additional Questions and Answers:
1. List the main features of gases.
a) Gases are highly compressible.
b) Gases excerts pressure equally in all directions
c) Gases mix evenly in all proportions without any mechanical aid
d) Gases are least dense than other two states of matter.
2. Give the formula for Charles law.
Volume α temperature
V α T
V = KT here V= volume T= temperature K = proportionality constant
3. List the applications of Charles law.
a) Soda bottles should store in cool and dry place.
b) Air balloons pops out during hot summer than in winter.
4. Give the formula for Boyle’s law.
V α 1 / P
V α K / P
PV =K here V= volume , P= Pressure , K = proportionality constant
5. List the applications of Boyle’s law.
a)Popping of balloon when squeezed due to increase in the pressure.
b) Deep sea fishes die when suddenly they brought to surface due to low pressure.
c) Scuba driver’s life is under threat when he suddenly comes to surface quickly.
6. State Graham’s law of diffusion.
“The rate of diffusion of gas is inversely proportional to the square root of its density”- This is called Graham’s law of diffusion
7. Give the formula for Graham’s law of diffusion
r α 1 / √d
r = K / √d
K = r x √d
here r = rate of diffusion, d = density of gas, K = proportionality constant
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