11th Class Chemistry Chapter 3 Gases Short Question Answers

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11th Class Chemistry Chapter 3 Gases Short Question Answers Below

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1.Why is the Boyle’s law applicable only to the ideal gases?
Boyle’s law is applicable to those gases which have no forces of attraction among the molecules.Such gases are ideal.So Boyle’s law is applicable to only ideal gases.Its formula is PV=K when n and T are constant.
2.When a gas obeys the Bolye’s law the isotherms for the gas can be plotted?
Isotherms are the graphs between pressure and volume at constant temperature and number of moles.This condition is fulfilled by Boyle’s law.The word isotherm means same temperature.They are curves.At higher temperature the curves go away from the axis.
3.What are isotherms?What happens to the position of isotherms when they are plotted at high temperature for a particular gas?
Isotherms are the graphs between pressure and volume when temperature is constant.These graphs are plotted keeping in view the Boyle’s Law.There are curves.When the isotherms are plotted at higher temperatures then they go away from the axis.The reason is that the volumes of the gases increase at high temperatures.In this way the points in the graph paper go away from the axis.
4.The product of pressure and volume at constant temperature and number of moles is a constant quantity.Why?
When the temperature and number of moles of a gas are constant then the increase of pressure decreases the volume in such a way that PV remains constant.By doubling the pressure the volume becomes half.We can say that,
P1V1 = P2V2 = P3V3 at constant temperature and number of moles.
5.Why do we get a straight line when pressures are plotted against inverse of volumes?This straight line changes its position in the graph by varying the temperature.justify it?
6.The plot of PV versus P is a straight line at constant temperature and with a fixed number of moles of an ideal gas.Why?
The product PV is a constant quantity when temperature and the number of moles are constant.So when we plot a graph between pressure on x-axis and PV on y-axis then a straight line paralllel to the pressure axis is obtained.This is verification of Boyle’s law.
7.What are various unit of pressure?
8.Greater the temperature of the gas closer the straight line of P versus 1/vto the pressure axis.justify it?
9.Charles’s law is not obeyed when the temperature is measured on celsius scale.Justify it?
10.What is absolute zero?What happens to real gases while approaching it?
It is the lowest possible temperature which would have been achieved if the substance remains in the gaseous state.All the real gases are converted to liquids above this temperature.This -273.16ᵒC is called zero absolute or zero kelvin.
11.A gas occupies 100 dm3 at 283 K.what will be its volume at -273ᵒC at constant pressure?
All the gases are converted into the liquid state before reaching -273ᵒC.It means that the concerned gas is liquid at 273ᵒC so volume of this gas at -273ᵒC cannot be predicted.
12.Throw some light on the factor 1/273 in Charles’s law?
13.Justify that the volume of given mass of a gas becomes theoretically zero at -273ᵒC?
14.How do you explain that -273ᵒC is theoretical temperature and is not attainable?
Actually gases becomes liquids before reaching -273ᵒC.Hence -273ᵒC is not an attainable temperature.We reach this temperature theoretically.If the volume of a gas would have been zero in the laboratory at -273ᵒC then law of conservation of mass would have been violated.
15.What are various scales of thermometer?Convert 80ᵒC to Fahrenheit?
16.How the value of the general gas constant’R can be derived with the help of Avogadro’s law?
17.Calculate the S.I.unit of R?
18.How the density of an ideal gas doubles by doubling the pressure or decreasing the temperature on Kelvin scale by ½?
19.What is Avogadro’s law of gasses?
20.Justify that 1 cm3 of H2 and 1 cm3 of CH4 at STP will have same number of molecules.When one molecule of CH4 is 8 time heavier that of hydrogen?
According to Avogadro’s law equal volumes of all the ideal gases at same temperature and pressure have equal number of molecules.So 1cm3 of H2 and 1cm3 of CH4 at STP will have an equal number of molecules.No doubt the molecule of methane is eight times heavier than H2 but the sizes of the gas molecules and their masses don’t disturb the volumes.The reason is that at STP one molecule of the gas is at a distance of three hundred time than its diameter.
21.Why pilots feel uncomfortable breathing at high altitude and divers cannot use normal air?
It is due to low partial pressure of O2 in the upper atmosphere.The pressure inside the lungs is greater than the partial pressure of O2 in the air.The pilots feel suffocation all attitudes.At the deoth of water the pressure is high so the partial pressure of O2 increases below water.The % of O2 in diver tank should be less than normal.
22.State Dalton’s law of partial pressures.Why is it necessary that no forces of attractions should be there to obey this law?
23.How do you say that the pressure of the dry gas is equal to the difference of total pressure and aqueous tension of H2O?
Some gases prepared in the laboratory are to be collected over water.So water vapor  join the gas.In order to get the pressure of the pure gas we have to subtract the vapor pressure of water  from the total pressure.
Pt  = Pgas+ aqueous tension
Pgas = Pt– aqueous tension
24.Lighter gases diffuse more rapidly than heavier gases.Give reason?
25.Gases deviate more from the general gas equation at 0ᵒC and deviate to less extent at 100ᵒC.Why?
Actually in kinetic molecular theory of gas we suppose that there are forces of attraction.At 0ᵒC the force of attractions are dominant and gases become non-ideal.At high temperature attractive forces become less dominant and gases behave ideally.
26.The actual volume of O2 gas at room temperature and 1 atm.Pressure is negligible as compared to volume occupied by one mole of this gas.But this actual volume is not negligible at high pressures.justify it?
At ordinary temperature and  pressure there are almost no forces of attractions among the molecules of O2.The actual volume of the gas molecules is negligible as compared to the volume of vessel.When the pressure is increased for O2,then molecules come close to each other.Collisions become move  frequent.Force of attraction start dominating actual volume remains no more negligible.
27.Hydrogen and helium are ideal at room temperature but SO2 and CI2 are non-ideal.How do you explain it?
H2 and he have very low boiling points.So at room temperature they are far away from their boiling points.At room temperature the attractive forces are absent.So they behave ideally.SO2and CI2 have boiling points close to room temperature but are below 0ᵒC.At room temperature they are not far away from their boiling points.Sufficient attractive forces are present at room temperature.So they are non-ideal.
28.How the critical temperature is an essential criteria to be considered for the liquefaction of gases?
Gases can be liquefied by increasing the pressure and decreasing the temperature.The temperature of a gas should reach the critical temperature on or below that to make the gas liquid.Gas can never be liquefied how much the pressure is applied if the gas is above the critical temperature.
29.Why the non-polar gases like H2 and he have a very low critical temperatures while polar gases like NH3 and SO2 have critical temperatures sufficiently above room temperature?
H2 and He are consisted of small-sized molecules and have low polarities.They have least forces of attractions among themselves.In order to liquefy them their  temperature have to bring close to absolute zero.NH3 and SO2 have attractive forces even at room temperature.In order to liquefy them their temperature may be above the room temperature.
30.In joule-Thomson effect sudden expansion of th e gas molecules needs energy.Why?
In the compressed state there are sufficient attractive forces among the molecules of the gas.During sudden expansion the energy is required to overcome the inter molecular attractions.Moreover the molecules need extra energy to run away in vacuum.
31.Joule-Thomson effect is operative in the Linde’s method of liquefaction of air.How?
In Licde’s method the gas is compressed to 200 atmospheric pressure.These compressed gases are suddenly allowed to expand through a nozzle.This sudden expansion of the gas and the consequent cooling is called joule-Thomson effect and this effect is operative in Linde’s method of liquefaction.
32.Why the gases deviate from ideal behavior at high pressure and low temperature?
When the temperature of the gases are low the attractive forces become dominant so gases don’t obey the gas laws.When the pressure of the gases are high,collisions become more frequent and force of attraction are created.Moreover the actual volume of the gas molecules are no more negligible as compared to the volume of the vessels.So two postulates of this theory are faulty.
33.Water vaporous do not behave ideally at 273 K.Why?
When wear vaporous are present at 273K (0 ᵒC) there are sufficient forces of attractions among its molecules at 0 ᵒC.Due to this reason water vaporous behave non-ideally at 273K.
34.Give two causes for deviation of gases from ideality?
The causes are due to two faulty assumptions. (i)Actual volume of the gas molecules is negligible as compared to the volume of vessel. (ii)There are no forces of attraction among the molecules of gases. These two postulates are correct when the temperature is high or pressure is low.
35.So2 is comparatively non-ideal at 273 K but behaves ideally at 327 K.Why?
SO2 gas is close to its boiling point at 273 K. So,at 273K attractive forces are dominating and make the gas non-ideal.But when the temperature of the gas is 327 K,then forces of attractions are less dominant and gas behaves ideally.
36.How the behavior of real gases is given by van Der waal’s equation?
The constant ‘a’and ‘b’ called van der waal’s constants give the qualitative measurements of attractive forces and sizes of the gas molecules.These parameters are very important for the real gases.
37.Why the pressure correction is done by van der waal?
The pressure is exerted due to collisions on the walls of vessel.Attractive forces decrease the intensity of collisions.SO the observed pressure on the walls is less than the ideal pressure.Lessened pressure is added in observed pressure to get ideal pressure.
38.Why the volume correction is done by van der wall?
The molecules of a gas do occupy certain volume which is not available to the gas molecules in the vessel.This is called excluded volume  and should be subtracted from the volume of vessel to get the free volume available to gas molecules.
Vfree =Vvessl –b
39.Why the excluded volume (b) is more than volume (Vm) of the gas?
Excluded volume ‘b’ is the volume of one mole of the real gas in the highly compressed state.But molar volume (Vm) is that volume when the same gas is liquefied and molecules are touching each other every moment.
So b= 4Vm
40.Why some amount of pressure should be added in the measured pressure of the non-ideal gas to get the ideal pressure of gas?
The forces of attractions hinder the molecules to collide the walls of the vessel with that force which should have been in the absence of attractive forces.It means that certain amount of pressure should be added in the measured pressure to get the ideal pressure.
So        Pi = P+P’
41.Pressure of NH3 gas at given conditions is less when calculated by Van der Wall’s equation than that calculated by general gas equation.Why?
NH3 is a polar gas and has forces of attractions in its molecules when the pressure is high.It show non-ideal behavior at high pressures.The factors ‘a’and ‘b’ become dominant at this pressure and van der Waal’s equation gives less pressure than calculated by general gas equation.
42.What is the Physical significance of van der wall’s constants ‘a’ and ‘b’?
43.What are characteristics of plasma?
The motions of particles in the plasma generate electrical currents from within plasma density.In this way the plasma is a unique fascinating and complex state of matter.The plasma is neutral overall.
44.Where is Plasma found?
It is the most abundant form of matter in the universe.It is stuff of stars.Our sun is 1.5. million km ball of plasma.On earth it occurs in flames auroras and fluorescent tubes.
45.What are application of Plasma?
(i)Glowing plasma inside the bulb. (ii)Neon signs (iii) Processing of semi-conductors. (iv) Sterilization of medical products.
46.Densities of gases are given in g dm-3 but not in g cm-3.Why?
Densities of gases are very low as compared to liquids and solids.To avoid the quantity of density to be written as negative power of 10 it is better to used bigger unit of vol.as dm3 in place of cm3 to keep the values which are easily understandable and comparable.

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