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__CHAPTER-18__

__CHAPTER-18__

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__Behaviour of Gases__

__Behaviour of Gases__

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__Text Book Question and Answers__

__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

**d. -273**

__c. -273__^{0}C^{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 /__
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273)

2. The S.I unit of temperature is ---------

3. The volume of gas diffusing per unit time is ---------

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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.

Volume α temperature

V α T

V = KT

a) Soda bottles should store in cool and dry place.

b) Air balloons pops out during hot summer than in winter.

V α 1 / P

V α K / P

PV =K

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.

“The rate of diffusion of gas is inversely proportional to the square root of its density”- This is called Graham’s law of diffusion

r α 1 / √d

r = K / √d

K = r x √d

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) |

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__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