1. What is the differences between Vapour and Gas?
Vapour Gas
Vapours are in solid or liquid state in ordinary Gases are in gaseous state under ordinary
conditions, but change into gaseous state under conditions (at room temperature and one
specific conditions. atmospheric pressure).
Vapour is not a state of matter. Gas is a state of matter.
Vapours experience a phase change, i.e., from Gases do not experience a phase change. Any
liquid to vapour form or from solid to vapour change in phase will change the state of gas
form. into liquid.
Vapour has a definite shape of the gaseous Gas does not a definite shape when it is
particles when observed under a microscope. observed under a microscope.
Natural state of vapour is not gaseous, but can
Natural state of a gas is the gaseous form.
be solid or liquid.
Vapour is a substance that is a combination of
Gas is a substance that has a single
gaseous and liquid phase in ordinary
thermodynamic state in ordinary conditions.
conditions.
Vapour is made of atoms and molecules that Gases are made of atoms and molecules that
move randomly. move randomly.
Vapours of water are around us all the time at Gases are usually formed above its critical
temperatures below the boiling point of water. temperature, but below critical pressure.
All vapour are gases. All gases are not vapour.
Gas cannot be liquefied by the application of
Vapour can be liquefied by pressure alone.
pressure alone.
Vapour may be visible. Gas is invisible.
Vapour settle down on the ground. Gases do not settle down on the ground.
2. Write the dimension of Shear stress and compare with that of Pressure.
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3. Explain that the different change of dynamic viscosity for gas and liquid with
temperature.
Viscosity is caused by the cohesive forces between the molecules in liquids and by the molecular
collisions in gases and it varies greatly with temperature.
In a liquid, the molecules possess more energy at higher temperatures and they can oppose the
large cohesive intermolecular forces more strongly. As a result, the energized liquid molecules can
move more freely.
In a gas, the intermolecular forces are negligible and the gas molecules at high temperatures move
randomly at higher velocities. This results in more molecular collisions per unit volume per unit
time and therefore in greater resistance to flow.
4. Determine the dynamic viscosity of a gas mixture which includes O2, N2, H2, CO2 with
molar ratio are 0.5, 0.4, 0.3 and 0.8 at 30oC.
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5. Calculate the dynamic viscosity of an emulsion containing 20 volume percent of cooking
oil in water at 20oC. Given the dynamic viscosity of oil equal 1.3 times for dynamic
viscosity of water at the same condition.
6. Calculate the dynamic viscosity of a suspension at 25oC including 25 volume percent of
solid particle dispersed phase in water.
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7. Calculate the density of the above gas mixture. Given the density of gas component we
can find out on Internet.
8. If the air is concerned as an ideal gas then determine the density of the air at 1 atm and
30oC.
9. Calculate the density of the above emulsion. Given the density of the oil is 900 kg/m3.
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10. Calculate the density of the above suspension. Given the specific gravity of the solid
particle dispersed phase is 1.5.
11. When you got the dynamic viscosity and the density of the above mixture. Let calculate
the kinetic viscosity.
