Behaviour of Gases ~ PHYSICAL SCIENCE Chapter 2 (class 10 wbbse) ( Important Short questions & Notes )

 

MADHYAMIK  PHYSICAL SCIENCE 

  SUGGESTION

Behaviour of Gases  ~ PHYSICAL SCIENCE 

1) What is the value of normal temperature? 

Ans. 0°C

2) What is the relation between pressure and density of a gas at constant temperature? 

Ans. Directly Proportional 

3) In which instrument pressure can be measured?  
Ans. Manometer

4) What is the value of absolute zero temperature in Fahrenheit scale?  
Ans. 459.4°F

5) What is the relation between kelvin scale and Celsius Scale ? 
Ans. T = t+273
[ T = temperature in Kelvin scale, 
t = temperature in Celsius scale  ]

6) What is the value of melting point of ice in kelvin scale?  
Ans. 273 K

7) What is the value of Avogardro's number? 
Ans. 6.022×10^23

8) What is torr ?
Ans. 1mm of Hg pressure.

9) What is the full form of SATP ?
Ans. Standard ambient temperature and pressure.

10) What is the value of bar in dyne/cm^2 ?
Ans. 10^6 dyne/m^2

11) Under what conditions is Boyle 's law is applicable?  
Ans. Temperature remaining constant.

12) What is the value of gas constant in S.I units ?
Ans. 8.31 j/mole K

13) Which is greater 30.C or 300K ?
Ans. 30°C

14) What are the constants of Boyle's law ? 
Ans. Temperature and Mass.

15) A gas initially at 0°C is heated so that its pressure and volume are both doubled. What will be its final temperature? 
Ans. 1092K or 819°C

16) What is  Avogadro's number? 
Ans. The number of molecules present in a gram - molecular mass of a substance is called the Avogadro's number.

17) What is Mole ? 
Ans. The gram - molecular mass of an element or a compound is known as its mole.
A mole represents the numbers of molecules (or atoms ) whose total mass equals the molecular  (or atomic) mass of the substance.

18) What is Molar volume ?
Ans. The molar volume is the volume occupied by one mole of substance at a given temperature and pressure. Molar volume of an ideal gas is 22.4L at STP.

19)  What are the constants of Charles' law ?
Ans. Pressure and Mass.

20) What is gaseous diffusion? 
Ans. Gaseous diffusion is a natural phenomena in which gases spontaneously mix with one another,  when they are in contact,  irrespective of their densities. This spontaneous mixing occurs, even against the gravity.

21) What is Absolute temperature scale? 
Ans. The temperature scale which has been set up by taking -273°C as zero point and each degree equal in magnitude to one degree in Celsius scale is termed as absolute scale of temperature. The temperature in this scale is stated as K (Kelvin) after the name of Lord Kelvin. The temperature -273°C is called absolute zero because at -273°C the volume of any gas would become zero and any temperature below this would correspond to a negative volume of gas.

22) What is Boyle's law ?
Ans. The Boyle's law states that - At constant temperature,  the volume of a given mass of a gas is inversely proportional to the pressure of the gas.

23) What is Charles' law? 
Ans. The Charles' law states that - At constant Pressure,  the volume of a given mass of a gas increases by 1/273 of its volume at 0°C for every 1°C rise in temperature.

24) When does the speed of gas molecules increase? 

Ans. Speed of gas molecules increases when heat energy or some other energy is supplied to the gas. 

25) What happens if molecular speed increases at constant volume? 

Ans. In such a case pressure of the gas increases , since , speeded up molecules strike the walls of container with greater force.

26) At what temperature does the speed of gas molecules become zero ?

Ans. At -273°C or 0 k speed of gas molecules becomes zero. 

27) What will happen to a gas filled ballon when heated and why ?

Ans. The balloon will burst . because,  due to supply of heat volume of the gas inside the balloon increases.

28) Why are gases highly compressible? 

Ans. In absence of mutual force of attraction, the intermolecular spaces between gas molecules are very large, so they can be very easily brought close to each  other , which means gases are highly compressible.

29) What is the number of molecules in 1.8g water ? (H=1, O=16)

Ans. 6023×1023

30) What is the number of molecules in 22.4 litre of ammonia at STP ? 

Ans. 6.023×1023

31) If the number of molecules in V litre of hydrogen gas at STP is n , what is the number of molecules in V/10 litre of CO2 gas at STP ?

Ans. Number of molecules in V/10 Litre of CO2 gas =  n/10.

32) How many atoms are present in one molecule of sulphuric acid ? 

Ans. 7 (H=2, S=1, O=4 )

33) How many molecules of carbon dioxide are present in 11 grams of carbon dioxide?  

Ans. 1.50575×1023

34) What would be the volume of 22 gram of carbon dioxide at standard temperature and pressure?  (C=12, O=16)

Ans. 11.2 litres. 

35) What is the mass of 1gm mole CO2? 

Ans. 1 mole CO2 = gm molecular mass of CO2 = Molecular mass expressed in gram = 44 gram

36) What is the atomic mass of oxygen?  

Ans. Atomic mass of oxygen is 16 a.m.u.

37) What is the relation between one mole and gram molecular mass? 

Ans. One mole of a molecule means its gram molecular mass.

38) a.m.u. stands for what ? 

Ans. a.m.u. is the abbreviation of atomic mass unit.

39) Name the element which is taken as the standard for measurement of atomic mass.

Ans. Carbon -12 isotope is taken as the standard for measurement of atomic mass. 

40) What is the volume of 1 gram mole of any gas at S.T.P.?

Ans. The volume of one gram mole of any gas at S.T.P is 22.4 litres.

41) What is Berzillus' hypothesis?  

Ans. Under same condition of temperature and pressure,  equal volumes of all gasses contain the same number of atoms. 

42)What is the relation between molecular weight and vapour density?  

Ans. Molecular weight is twice the vapour density. 

42) Write the equation formed by combining Boyle's law and Charles law. What do the symbols used in this equation indicate?  

Ans. The ideal gas equation is given by PV = nRT 

Where 

P= Pressure of the gas ( in atm)

V  = Volume of the gas  (in litres)

 T = Temperature of gas (in kelvin )

  n  = number of moles of the gas 

 R  = Universal Gas constant = 0.0821 l atm k-1 mol-1

43) When a balloon is inflated the volume increases with the increase of pressure. Does it contradict Boyle's law ? Explain.

Ans. When a balloon is inflated the volume increases with the increase of pressure. But simultaneously mass of the gas also increases as more air is pumped into the balloon.  But according to the Boyle's law , mass of the gas must be constant. Hence,    it doesn't violate Boyle's law.

44) The size of weather balloon becomes larger as it ascends into higher altitudes.  Why? 

Ans. At higher altitudes,  the atmospheric pressure is less. Therefore,  the gas filled in the balloon expands more and more as the balloon goes higher. This explains Boyle's law. 

45) Why the tyre of an automobile is inflated to a lesser pressure in summer than in winter ? 

Ans. In summer,  the room temperature is much higher as compared to winter. Consequently , the same volume of air will exert greater pressure in summer. Therefore, it is always advisable to inflate the tyre to lesser extent in summer as compared to winter to avoid the bursting of tyres.

46) What is effusion of a gas ? 

Ans. It is the passage of a gas under pressure through a tiny hole in a container. Process of effusion is used to separate the isotopes of an element. During effusion,  the lighter isotopes escape first from the pores of the container leaving behind the heavier isotopes.

47)Why are aerated bottles kept under water during summer?  

Ans. Aerated water bottles contain carbon dioxide gas dissolved in aqueous solution under pressure.  In summer,  the solubility of the gas in solution decreases with rise in temperature.  Consequently,  the amount of free gas in bottles increases.  This leads to increase in pressure.  Thus , the bottles may explode. To avoid explosion,  bottles are kept under cold water in summer.

48) When air bubbles rise from the lower level to upper level of water in a pond their volume increases. Why ? 

Ans. When an aur bubble rises up from water,  then the pressure of water on the bubble gradually decreases. According to Boyle's law , at constant temperature,  pressure on the gas in inversely proportional to its volume. Hence , assuming that the temperature throughout the water remains constant,  the volume of the bubble goes on increasing due to gradual decrease of pressure on it. For this reason, volume of a bubble gradually increases when it rises up through water in pond. 

49) Explain the practical significance of Charles law.

Ans. The working of hot air balloons used in sports and for meteorological observations is based on Charles law. These balloons are filled with hot air which takes up in the sky. This is because the gases expand on heating. The hot air is less dense and displaces the cooler air of atmosphere. This causes the balloon to rise up in the sky.

50) Why does a gas exert pressure?  

• Ans . Pressure is exerted due to the collision of the gaseous molecules with the walls of the vessel or with any other surface in contact with the gas. The pressure of the gas is defined as the force exerted by the gas molecules per unit area of the wall.