Physical matter states|9th class chemistry|tutoronlines

chapter # 5



Table of contact:

Sr. No Name of Topics
1 Pressure and it unit
2 Diffusion and Effusion
3 Density of Gas and Liquid
4 Intermolecular forces
5 Charle’s law
6 Boyle’s law
7 Evaporation
8 Condensation
9 Evaporation causes

Give the answer these following question.

Q.No.1. Define pressure? Write down its unit.
Ans. Pressure:

The force exerted per unit surface area ( A ) is called pressure. That the force which is exerted by a gas on per unit area is called its pressure. The pressure is represented by P.
P= F/A
The S.I unit of force is Newton, and unit of area is m2, So the unit of pressure is N/m2, it is also known as Pascal. P=1N/m2

Q.No.2. Define standard atmospheric pressure?

Ans. A pressure exerted by atmosphere at the sea level. It can be defined as. The pressure exerted by a mercury column of 760mm height at sea level.
1atm = 760mm of Hg
= 760 torr (1mm of Hg = One torr)
101325 N/m2
= 101325 Pa

Q.No.3. Define the term effusion and give one example?

Ans. The escaping of gas molecules through a tiny hole into a space toward area of low pressure. e.g when a tyre get punctured, air effuse out.

Q.No.4. Differentiate between diffusion and effusion?

Spontaneous mixing up of gas molecules by random motion and collision is called diffusion. Diffusion depends upon the molecular mass of gases. Lighter gases diffuse rapidly.


Escape of gas molecule through a tiny hole to an evacuated space.” e.g. when a tyre gets punctured, all the air effuses out. Effusion also depends upon molecular mass.

Q.No.5. Why the gases are compressible?

Ans. The molecule of gases are farther apart. There is blank spaces among them, so by compressing, these spces reduced.

Q.No.6. Why the density of gases is lesser than that of liquid?

Ans. Because the gas molecules have very large spaces among them. Hence their light mass and more volume; gases have low densities.

Q.No.7. When the density of gases is lesser than that of liquids?

Ans. On cooling the molecules have very large spaces among them. Hence their light mass and more volume; gases have low densities.

Q.No.8. Which factors affect diffusion of liquids?

Ans. The diffusion of liquid depend upon following factors.

1. Intermolecular forces:

The rate of diffusion is high in those molecules who have weak intermolecular forces.

2. Size of molecules:

Large size molecules have slow rate of diffusion.

3. Shape of molecules:

The molecules of proper shape can be easily diffused.

4. Temperature:

Higher the temperature higher the diffusion will be.

Q.No.9. What is meant by freezing point?

Ans. That temperature at which vapour pressure of liquid phase is equal to vapour pressure of solid phase. At this temperature liquid and solid coexist in dynamic equilibrium with one another.

Q.No.10. Why is the density of gas measured in g/dm3 while that of liquid in g/cm3?

Ans. The density of gas is less than that of liquid, that is why density of gas is expressed in g/dm3 and that of liquid in g/cm3.

Q.No.11. On which two factor evaporation depends on?

Ans. Evaporation depends upon following factors;

1. Surface area
2. Temperature

Q.No.12. What do you mean by pascal? How many pascal is equal to 1 atm?

Ans. If one Newton force exerted perpendicular to area of 1 meter square, then the pressure exerted on a body is equal to one pascals.
1 atm = 101325 Pa

Q.No.13. Define charle’s Law?
Ans. Charle’s law:

The law was put forward by a French scientist J. Charles in 1787. This is law states that,
The volume of given mass of a gas is directly proportional to the absolute temperature at constant pressure.
V = kT, k= V/T

Q.No.14. Differentiate between Boyle’s law and Charle’s law?


Sr. No Boyle’s law Charle’s law
1 Boyles studies the relation between gas volume and pressure at constant temperature. Charles studies the relation between gas volume and temperature at constant pressure.
2 He observed “If temperature is kept constant the volume of mass of gas is inversely proportional to its pressure.” He observed “If Pressure is kept constant the volume of mass of a gas is directly proportional to it temperature.

Q.No.15. Define Boyle’s law and write down its mathematical expression?

Ans. In 1662, Robert Boyle studies the relation between gas volume and pressure at constant temperature.

According to law:

If temperature is kept constant the volume of mass of gas is inversely proportional to its pressure.
VP = k

Q.No.16. What is absolute zero temperature?

Ans. That temperature at which the volume of an ideal gas become zero. Its value is negative 273.15 degree.

Q.No.17. Convert 50C into Kelvin scale?

Ans. K = TC + 273
= 50C + 273
K = 323k

Q.No.18. Why vapour pressure is higher at high temperature?

Ans. At high temperature vapour pressure is higher than at low temperature. Because at elevated temperature, the kinetic energy of the molecules increases enough to enable them to vaporize and exert pressure.

Q.No.19. What is meant by evaporation?

Ans. The process in which liquid state changes in vapour state is called evaporation. This process occurs only at liquid surface. Greater the surface of liquid greater will be evaporation.

Q.No.20. What is meant by condensation?
Ans. Condensation:

A process in which gaseous phase changes into liquid phase is called condensation.

Q.No.21. Why are the rates of diffusion in liquids slower than that of gasses?

Ans. In gases, the molecules moves freely and have less force of attraction among them. So they occupy all the available space. Instead in liquids molecules have strong force of attraction as compared to gases so they are less mobile, that’s the reason why liquid diffuse slowly.

Q.No.22. Why does evaporation increase with increase of temperature?

Ans. At high temperature, rate of evaporation becomes fast, because at high temperature, the kinetic energy of molecules become very high and over come the intermolecular forces. For example water level in hot water container decreases earlier than than that of cold water. This is because the hot water evaporate earlier.

Q.No.23. Why are the liquids are mobile?

Ans. Among the molecules of liquid intermolecular forces are not much strong, to keep them stationary, instead the molecules keeps on moving freely under the surface of liquid. That’s why liquid have not definite shape but have definite volume.

Q.No.24. Why is the boiling point of water higher than that of alcohol?

Ans. The intermolecular forces in water are much strong than that of alcohol, that is the reason why water has high boiling point.

Q.No.25. Why evaporation causes cooling?

Ans. Evaporation is a cooling process when the high kinetic energy molecules evaporation the temperature of remaining molecule fall down. To compensate this deficiency of energy, molecules of liquid absorb energy from surrounding . As a result temperature of surrounding decreases and we cool effect.

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