Selina solutions concise chemistry class 9 icse Solutions for Chapter 7 chapter 7 study of gas laws

What do you understand by gas

Give the assumptions of the kinetic molecular theory

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

What is diffusion ? Give an example to illustrate

How is molecular motion related with temperature.

State

(i) the three variables for gas laws

ii) S.I units of these variables.

(a) State Boyle’s Law.

(b) Give its

(i) mathematical expression,

(ii) graphical representation and

(iii) significance

Explain Boyle’s law on the basis of the kinetic theory of matter.

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 temperature constant

(a) State Charles law

(b) Give its

(i) Graphical representation,

(ii) mathematical expression and

(iii) Significance

Explain Charles’s law on the basis of the kinetic theory of matter

Define absolute zero and absolute scale of temperature. Write the relationship between °C and K.

(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 a centigrade scale

(a) Define S.T.P.

(b) Why is it necessary to compare gases at S.T.P.?

Write the value of

a) Standard temperature in

i) °C ii) K

b) Standard pressure in

i) atm ii) mmHg iii) cm Hg iv) torr

State the laws which are represented by the following graphs.

Give reasons for the following

a) All temperatures in the absolute (Kelvin) 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 gas while stating its volume.

e) Inflating balloon seems to violate Boyle’s law.

f) Mountaineers carry oxygen cylinders with them.

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

How did Charles’s law lead to the concept of an absolute scale of temperature

What is meant by aqueous tension? How is the pressure exerted by a gas corrected to account for aqueous tension

State the following (a) Volume of a gas at 0 Kelvin.

(b) Absolute temperature of a gas at 7°C.

(c) Gas equation.

(d) Ice point in absolute temperature.

(e) S.T.P. conditions

Choose the correct answer (a) The graph of PV vs P for gas is

(i) parabolic

(ii) hyperbolic

(iii) a straight line parallel to X-axis

(iv) a straight line passing through the origin

(b) The absolute temperature value that corresponds t 27°C is

(i) 200K

(ii) 300K

(iii) 400K

(iv)246K

c) Volume-Temperature relationship is given by

(i) Boyle

(ii) Gay Lussac

(iii) Dalton

(iv) Charles

(d) If the pressure is doubled for a fixed mass of gas, its volume will become

(i) 4 times

(ii)1/2 times

(iii)2 times

(iv) No change

Correct the following statements.

(a) Volume of a gas is inversely proportional to its pressure at constant temperature.

(b) Volume of a fixed mass of a gas is directly proportional to its temperature, pressure remaining

constant.

(c) 0°C is equal to zero Kelvin.

(d) Standard temperature is 25°C.

(e) Boiling point of water is 273 K.

Fill in the blanks

(a) The average kinetic energy of the molecules of is proportional to the ………….

(b) The temperature on the Kelvin scale at which molecular motion completely ceases is called ……….

(c) If temperature is reduced to half, …….would, also reduce to half.

(d) The melting point of ice is ……….. Kelvin.

What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 temperature

remaining constant.

2 liters of agas is enclosed in a vessel at a pressure of 760 mm Hg. If the temperature remains constant,

calculate the pressure when the volume changes to 40 dm3.

At constant temperature, the effect of change of pressure on the volume of a gas was as given below:

(a) Plot the following graphs

1. P vs V 2. P vs 1/V 3. PV vs P

b) Assuming that the pressure values given above are correct, find the correct measurement of the volume

at 0.60 atmospheric pressure

800 cm3 of gas is collected at 654 mm pressure. At what pressure would the volume of the gas reduce by 40% of its original volume, the temperature remaining constant.

the cylinder of 20 liters capacity contains gas at atmospheric pressure. How many flasks of 200 cm3 capacity can be filled from it at 1 atmosphere pressure, temperature remaining constant ?

A steel cylinder of internal volume 20 litres is filled with hydrogen at 29 atmospheric pressure. If hydrogen is used to fill a balloon at 1.25 atmospheric pressure at the same temperature, what volume will the gas occupy

561 dm3 of gas at S.T.P. is filled in a 748 dm3 Container. If the temperature is constant, calculate the\ percentage change in pressure required.

88 cm3 of nitrogen is at a pressure of 770 mm of mercury. If the pressure is raised to 880 mm Hg, find by

how much the volume will diminish, the temperature remains Constant.

A gas at 240 K is heated to l27°C. Find the Percentage change in the volume of the gas (pressure remaining constant).

A certain amount of a gas occupies a volume of 0.4 liters at 17o c. To what temperature should it be heated so that its volume gets (a) doubled (b) reduced to half, pressure remaining constant

given mass of a gas occupies 143 cm3 at 27°C and 700 mm Hg pressure. What will be its volume at 300 K and 180 mm Hg pressure

gas occupies 500 cm3 at normal temperature. At what temperature will the volume of the gas be

reduced by 20% of its original volume, pressure being constant?

Calculate the final volume of a gas ‘X’, if the original pressure of the gas, at S.T.P. is doubled and its temperature is increased three times.

A sample of carbon dioxide occupies 30 cm3 at 15°C and 740 mm pressure. Find its volume at S.T.P.

15. What temperature would be necessary to double the volume of a gas, initially at S.T.P., if the pressure is

decreased to 50%.

At 0oc and 760 mm Hg pressure, a gas occupies a volume of 100 cm3. Kelvin temperature of the gas is increased by one-fifth and the pressure is increased one and a half times. Calculate the final volume of the gas.

It is found, on heating a gas, its volume increases by 50%, and pressure decrease to 60% of its original value. If the original temperature was-15’C, find the temperature to which it was heated

A certain mass of a gas occupies 2 liters at 27oC and 100 pascals. Find the temperature when volume and pressure become half of their initial values

2500 cm3 of hydrogen is taken at S.T.P.The pressure of this gas is further increased by two and a half times (temperature remaining Constant). What volume will hydrogen occupy now?

Taking the volume of hydrogen as calculated in Q.19, what change must be made in Kelvin( absolute) temperature to return the volume to 2500 cm3 ( pressure remaining constant)

A given amount of gas A is confined in a chamber of constant volume. When the chamber is immersed in a bath of melting ice, the pressure of the gas is 100 cm Hg.

(a) What is the temperature, when the pressure is 10 cm Hg

(b) What will be the pressure, when the chamber is brought to 100°C?

Agas is to be filled from a tank of capacity 10,000 liters into cylinders each having capacity of 10 liters.

The condition of the gas in the tank is as follows

(a) pressure inside the tank is 800 mm of Hg.

(b) the temperature inside the tank is —3°C.

When the cylinder is filled, the pressure gauge reads 400 mm of Hg and the temperature is 270 K. Find the

a number of cylinders required to fill the gas.

Calculate the volume occupied by 2 g of hydrogen at 27°C and 4-atmosphere pressure, if at S.T.P. it occupies 22.4 liters

50 cm3 of hydrogen is collected over water at 17°C and 750 mm Hg pressure. Calculate the volume of dry gas at S.T.P. The water vapor pressure at 17°C is 14 mm Hg.

Which will have greater volume when the following gases are compared at S.T.P

a) 1.2 l N2 at 25oc and 748 mm Hg

b) 1:25 l O2 at S.T.P

Calculate the volume of dry air at S.T.P. that occupies 28 cm3 at 14°C and 750 mm Hg pressure when saturated with water vapour. The vapor pressure of water at 14°C is 12 mm Hg

L.P.G. cylinder can withstand a pressure of 14.9 atmospheres. The pressure gauge of the cylinder indicates 12 atmospheres at 27°C. Due to a sudden fire in the building the temperature rises. At what

temperature will the cylinder explode.

22.4 liters of gas weighs 70 g at S.T.P. Calculate the eight of the gas if it occupies a volume of 20 liters

at 27oC and 700 mm Hg of pressure.