Study of Gas Laws Exe-7 Short Answer Chemistry Class-9 ICSE Selina Publishers

Study of Gas Laws Exe-7 Short Answer Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-7. Step By Step ICSE Selina Concise Solutions of Chapter-7 Study of Gas Laws with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

Study of Gas Laws Exe-7 Short Answer Chemistry Class-9 ICSE Concise Selina Publishers

Board ICSE
Publications Selina Publication
Subject Chemistry
Class 9th
Chapter-7 Study of Gas Laws
Book Name Concise
Topics Solution of Exercise – 7 Short Answer Type
Academic Session 2023-2024

C. Exercise – 7 Short Answer Type

Study of Gas Laws Class-9 Chemistry Concise Solutions  

Page-132

Question 1.

What do you understand by gas?

Answer:

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.

What is diffusion? Give an example to illustrate it.

Answer:

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 3.

How is molecular motion related with temperature?

Answer:

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

Question 4. 

Define absolute zero and absolute scale of temperature.

Answer:

Absolute zero

The temperature -273°C is called absolute zero.

absolute zero

Absolute or Kelvin scale of temperature

The temperature scale with its zero at -273°C and each degree equal to one degree on the Celsius scale is called Kelvin or the absolute scale of temperature.

Question 5.

(a) Define STP.

(b) Why is it necessary to compare gases at STP?

Answer:

(a) Standard or Normal Temperature and Pressure (STP or NTP)

The pressure of the atmosphere which is equal to 76 cm or 760 mm of mercury and the temperature is 0°C or 273 K is called STP or NTP. The full form of STP is Standard Temperature  and Pressure, while that of NTP is Normal Temperature and Pressure.

Value: The standard values chosen are 0°C or 273 K for temperature and 1 atmospheric unit (atm) or 760 mm of mercury for pressure.

stp

The standard values chosen are 0°C or 273 K for temperature and 1 atmospheric unit (atm) or 760 mm of mercury for pressure.

Standard temperature = 0°C = 273 K

Standard pressure = 760 mmHg

= 76 cm of Hg

= 1 atmospheric pressure (atm) 

(b) The volume of a given mass of dry enclosed gas depends on the pressure of the gas and the temperature of the gas in Kelvin, so to express the volume of the gases, we compare these to STP.

Question 6.

State the laws which are represented by the following graphs.
State the laws which are represented by the following graphs.

Answer:

(a) Charles’ law

(b) Boyle’s law

Question 7.

What is the relationship between the Celsius and the Kelvin scales of temperature?

Answer:

The size of 1 degree on the Kelvin scale is the same as the size of 1 degree on the Celsius scale i.e., unit size on Kelvin scale is equal to the unit size on Celsius scale.
The value on the Celsius scale can be converted to Kelvin scale by adding 273 to it. Kelvin scale values can be converted to degree Celsius values by subtracting 273 from it.

Question 8.

The molecular theory states that the pressure exerted by a gas in a closed vessel results from the gas molecules striking against the walls of the vessel. How will the pressure change if

(a) The temperature is doubled keeping the volume constant

(b) The volume is made half of its original value keeping the T constant

Answer:

(a) Pressure will double.

(b) Pressure remains the same.

Question 9.

(a) What is the need for the Kelvin scale of temperature?

(b) What is the boiling point of water on the Kelvin scale? Convert it into centigrade scale.

Answer:

(a) The behavior of gases shows that it is not possible to have temperature below 273.15°C. This act has led to the formulation of another scale known as the Kelvin scale. The real advantage of the Kelvin scale is that it makes the application and the use of gas laws simple. Even more significantly, all values on the Kelvin scale are positive.

(b) The boiling point of water on the Kelvin scale is 373 K. Now, K = °C + 273 and °C = K – 273.

The Kelvin scale can be converted to the degree Celsius scale by subtracting 273 So, the boiling point of water on the centigrade scale is 373 K – 273 = 100°C.

Question 10.

Give reasons for the following:

(a) All temperature in the absolute (Kelvin) scale are in positive figures.

(b) Gases have lower density compared to 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 them.

(g) Gas fills the vessel completely in which it is kept.

Answer:

(a) The advantage of the Kelvin scale is that it makes the application and use of gas laws simple. Of more significance is that all values on the scale are positive, removing the problem of negative (-) values on the Celsius scale.

(b) The mass of a gas per unit volume is small because of the large intermolecular spaces between the molecules. Therefore, gases have low density. In solids and liquids, the mass is higher and intermolecular spaces are negligible.

(c) At a given temperature, the number of molecules of a gas striking against the walls of the container per unit time per unit area is the same. Thus, gases exert the same pressure in all directions.

(d) Because the volume of a gas changes remarkably with a change in temperature and pressure, it becomes necessary to choose a standard value of temperature pressure.

(e) When a balloon is inflated, the pressure inside the balloon decreases, and according to Boyle’s law, the volume of the gas should increase. But this does not happen. On inflation of a balloon along with reduction of pressure of air inside the balloon, the volume of air also decreases, violating Boyle’s law.

(f) Atmospheric pressure is low at high altitudes. The volume of air increases and air becomes less dense because volume is inversely proportional to density. Hence, lesser volume of oxygen is available for breathing. Thus, mountaineers have to carry oxygen cylinders with them.

(g) Interparticle attraction is weak and interparticle space is large in gases because the particles are completely free to move randomly in the entire available space and takes the shape of the vessel in which the gas is kept.

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