Question

Give reasons for the following:
(a) all temperatures in the absolute (Kelving) scale are in positive figures.
(b) Gases have lower density compared to that of solids or liquids.
(c) Gases exert pressure in all directions.
(d) It is necessary to specify the pressure and temperature of a gas while stating its volume.
(e) inflating a balloon seems to violate Boyle's law.
(f) Mountaineers carry oxygen cylinders with theml.
(g) gas fills completely the vessel in which it is kept.

Answer 1

a)The lowest temperature on the Kelvin scale is taken as 0 Kelvin or -273⁰ C. It is supposed that at this temperature, the volume of any gas becomes zero which is not possible. Thus any temperature taken in Kelvin scale is always positive.
b)As the volume of the substance increases, its density decreases. Gases havehigher intermolecular space compared to solids and liquids. As the molecules in agas are spread apart, they have comparatively lesser number of molecules in a given volume , as compared to solids and liquids
c)The molecules are continually colliding with each other and with the walls of the container. When a molecule collides with the wall, they exert small force on the wall The pressure exerted by the gas is due to the sum of all these collision forces.The more particles that hit the walls, the higher the pressure
d)It is necessary to specify the temperature and pressure of the gas while stating its volume because volume of gas changes by varying temperature andpressure. When we increase the pressure on the gas, volume of gas decreases and on decreasing pressure, reverse happens.
e)When we squeeze the inflated balloon the volume decreases and simultaneously pressure inside it increases. Thus Boyle's law is not violated actually which says PV= constant or Pressure and volume are inversely proportional at constant temperature.
f)As we go higher and higher the pressure and the oxygen decrease so as due to less oxygen content they carry oxygen cylinders. Mountaineer's carry oxygen cylinders because when they go high the the altitude decrease and the level ofoxygen goes down so they carry oxygen cylinders.
g)The force of attraction between particles of gas is negligible. Because of this, particles of gas move in all directions. Thus, a gas fills the vessel completelyin which it is kept. ... Because of this a gas exerts pressure on the walls of the container in which it is kept.