Chapter-7 Study of Gas Laws Class-9 Concise Selina Solutions . Step by Step Selina Concise Solutions for ICSE Class-9 Chemistry of Chapter-7 Exercise Questions . The Solutions of Numerical Based on Boyel’s Law, (Page 119) , Numerical Based on Charles’ Law, (Page 122) , Exercise-7 for Selina Concise Chemistry ICSE Class-9. Visit official website cisce for detail information about icse class -9 Chemistry.

## Chapter-7 Study of Gas Laws Class-9 Concise Selina Solutions

–: Select Topics :–

Numerical Based on Boyel’s Law, (Page 119)

Numerical Based on Charles’ Law, (Page 122)

Exercise-7,

### Numerical Based on Boyel’s Law, (Page 119) Study of Gas Laws Chapter-7 Selina Chemistry Solutions Class 9

#### Question 1

Volume of certain amount of a gas at 25°C and 100 cm Hg pressure is 80 mL. The gas is expanded to 160 mL keeping the temperature constant. Calculate the pressure of the expanded gas. #### Question 2

At a particular temperature, a certain quantity of gas occupies a volume of 74 cm at a pressure of 760 mm. If the pressure is decreased to 740 mm, what will be the volume of the gas at the same temperature ? #### Questions 3

L A student performed an experiment to measure pressure and volume of a gas at constant temperature and noted the following :

……………

Calculate the value of x and y. Which law was used in the calculations ? Draw a suitable graph. #### Question 4.

At a constant temperature, volume of a gas was found to be 400 cm’ at a pressure of 760mm Hg. If the pressure of the gas is increased by 25%, find the new volume. #### Question 5.

A vessel of capacity 600 cm³ contains hydrogen gas at a pressure of 330 cm Hg. What will be the pressure of hydrogen gas, when the vessel is connected to another vessel of 300 cm capacity ? #### Questions 6

At constant temperature, a gas is at a pressure of 1080 mm Hg. If the volume is decreased by 40%, find the new pressure of the gas. ### Numerical Based on Charles’ Law, (Page 122) Study of Gas Laws Chapter-7 Selina Chemistry Solutions Class 9

Question 1.

Convert the following :
(i) 37 K to °C
(ii) 273 K to °C
(iii) -27°C toK
(iv) 27°C to K #### Question 2.

20 mL of hydrogen gas at -13°C is heated to 117°C at constant pressure. Find the new volume of hydrogen. Question 3.

At what temperature in degree centigrade will the volume of a gas, which is originally at 0°C, double itself, pressure remaining constant. Question 4.

Calculate the volume (in cm³) of air expelled from a vessel containing 0-4 litres of it at 250 K, when it is heated to 27°C at the same pressure. Question 5.

What will be the volume of a gas when 3 litres of it is cooled down from 27°C to -73°C at constant pressure. Question 6.

To what temperature must a gas at 300 K be cooled down in order to reduce its volume to 1/3rd of its original volume, pressure remaining
constant ? Question 7

Prove that the volume of a gas at 273°C is twice its volume at 273 K, at constant pressure. Question 8.

A gas occupies 3 litres at 0°C. What volume will it occupy at -20°C, pressure remaining Exe-7 Study of Gas Laws Chapter-7 Selina Chemistry Solutions Class 9

#### Question 1

What do you understand by gas?

Gas is a state of matter in which inter particle attraction is weak and inter particle space is so large that the particles become completely free to move randomly in the entire available space.

#### Question 2

Give the assumptions of the kinetic molecular theory.

1. Gases are made of tiny particles which move in all possible directions at all possible speeds. The size of molecules is small as compared to the volume of the occupied gas.
2. There is no force of attraction between gas particles or between the particles and the walls of the container. So, the particles are free to move in the entire space available to them.
3. The moving particles of gas collide with each other and with the walls of the container. Because of these collisions, gas molecules exert pressure. Gases exert the same pressure in all directions.
4. There is large inter particle space between gas molecules, and this accounts for high comprehensibility of gases.
5. Volume of a gas increases with a decrease in pressure and increase in temperature.
6. Gases have low density as they have large inter molecular spaces between their molecules.
7. Gases have a natural tendency to mix with one and other because of large inter molecular spaces. So, two gases when mixed form a homogeneous gaseous mixture.
8. The inter molecular space of a gas is reduced because of cooling. Molecules come closer resulting in liquefaction of the gas.

#### Question 3

During the practical in the lab when hydrogen sulphide gas having offensive odour is prepared for some test, we can smell the gas even 50 metres away. Explain the phenomenon.

The phenomenon is diffusion. In air, gas molecules diffuse to mix thoroughly. Hence, we can smell hydrogen sulphide gas from a distance in the laboratory.

#### Question 4

What is diffusion? Give an example to illustrate it.

Diffusion is the process of gradual mixing of two substances, kept in contact, by molecular motion.

Example:

If a jar of chlorine is opened in a large room, the odorous gas mixes with air and spreads to every part of the room. Although chlorine is heavier than air, it does not remain at the floor level but spreads throughout the room.

#### Question 5

How is molecular motion related with temperature?

Temperature affects the kinetic energy of molecules. So, molecular motion is directly proportional to temperature.

#### Question 6 State

(i) the three variables for gas laws and

(ii) SI units of these variables.

(i) Three variables for gas laws: Volume (V), Pressure (P), Temperature (T)

(ii) SI units of these variables:

For volume: Cubic meter (m3)

and For pressure: Pascal (Pa)

For temperature: Kelvin (K)

#### Question 7

(a) State Boyle’s Law.

(b) Give its

(i) Mathematical expression

(ii) Graphical representation and

(iii). Significance

##### (a) Boyle’s law:

At constant temperature, the volume of a definite mass of any gas is inversely proportional to the pressure of the gas.

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