Matter

Question 1

What is Boyle’s law?

Answer 1

It states that for a fixed mass (or moles) of gas at a constant temperature, the product of pressure and volume of the gas is constant.
𝑖. 𝑒.
𝑷𝑽 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕 (𝑎𝑡 𝑎 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒)

Or
The volume of a fixed mass of a gas is inversely proportional to its pressure at a constant temperature.

Question 2

What is Charles’ law?

Answer 2

It states that the volume of a fixed mass (or moles) of a gas at a constant pressure is directly proportional to its absolute temperature.

𝑖.𝑒.
𝑽 ∝𝑻(𝑎𝑡𝑎𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒)

𝑜𝑟

𝑽/𝑻 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕 (𝑎𝑡 𝑎 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒)

Question 3

What is Avogadro’s law

Answer 3

It states that equal volumes of gases at the same temperature and pressure contain the same number of molecules.

Question 4

Define Partial pressure

Answer 4

This is the pressure that a gas in a mixture would exert if it were to occupy the whole volume of the container alone at the same temperature as the mixture.

Question 5

What does Dalton’s law of partial pressure state?

Answer 5

When two or more gases which do not chemically react are present in a container, the total pressure exerted by the mixture is the sum of the partial pressures of the individual gases

Question 6

Define mole fraction

Answer 6

The number of moles of a component divided by the total number of moles in the mixture

Question 7

True or false
The sum of mole fractions is always equal to 1

Answer 7

True

Question 8

Define Diffusion

Answer 8

This is the movement of molecules of a substance from where they are more concentrated to where they are less concentrated until a homogeneous mixture is formed.

Question 9

What is Graham’s law of diffusion?

Answer 9

It states that the rate of diffusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure i.e.

𝑹𝒂𝒕𝒆 ∝ √1/𝝆

or 𝑹𝒂𝒕𝒆√𝝆 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕;

Where 𝜌 = density of the gas

𝑹𝒂𝒕𝒆 ∝ √1/ 𝑴r

Question 10

Explain the factors affecting rate of diffusion of gases

Answer 10

a) Temperature of the system since average kinetic energy of gas molecules is proportional absolute temperature

b) Concentration/pressure of the gas; rate of diffusion increases with concentration/pressure

c) Density/ relative molecular mass of the gas; rate of diffusion is inversely proportional to the density/relative molecular mass of the gas

Question 11

What is Effusion?

Answer 11

Effusion is the escape of a gas through a small hole.

Question 12

What Factors affect effusion

Answer 12

1. Density of a gas
2. Temperature of the surrounding
3. Size of the hole

Question 13

Define an Ideal gas

Answer 13

This is a gas that obeys gas laws and the ideal gas equation at all temperatures and pressure.

Question 14

What are the characteristics of ideal gases?

Answer 14

• They have no intermolecular forces of attraction or repulsion
• Their molecules occupy zero volume
• Their molecules have very high kinetic energy
• Their compressibility factor is 1

Question 15

What are Real gases?

Answer 15

These are gases that do not obey the gas laws and the ideal gas equation at all temperatures and pressure.

This is due to presence of intermolecular forces of attraction and their molecules occupying a considerable volume relative to that of the container.

Question 16

Give characteristics of real gases

Answer 16

• They experience intermolecular forces of attraction (Van der waal forces of attraction or hydrogen bonding).
• Their molecules are big enough to occupy reasonable space/volume
• Their molecules do not have very high kinetic energy
• Their compressibility factor is not always 1

Question 17

Why can’t real gases obey gas laws at every temperature and pressure?

Answer 17

a) Co-volume of a gas
Real gas molecules are big enough to occupy some considerable volume of the container and this is called the co-volume

(b) Intermolecular forces of attraction
At low temperatures and high pressure the intermolecular forces of attraction become significant.

Under these conditions gas molecules attract each other strongly and this may cause the gas to liquefy or even to solidify.

For a gas molecule moving towards the walls of the container will experience two attractive forces; one from other molecules in the bulk of the gas and another from the particles that constitute the walls of the container.

Question 18

Define compressibility factor

Answer 18

This is the ratio of the molar volume of a gas compared to the molar volume of the ideal gas at the same conditions.

Question 19

What factors affect liquefaction of gases?

Answer 19

a) Decrease in temperature
- Decrease in temperature favors liquefaction of gases.
- This is because the kinetic energy of the gas molecules is reduced, the molecules come closer and the intermolecular force of attraction between them increases.

b) Increase in pressure
- Increase in pressure favors liquefaction of gases.
- This is because increases in pressure brings the molecules closer thereby increasing the intermolecular forces of attraction between them.

Question 20

Define critical temperature

Answer 20

This is the temperature above which a gas cannot be liquefied by increase in pressure alone without further cooling.

Question 21

What is critical pressure?

Answer 21

The minimum pressure required to liquefy a gas at its critical temperature

Question 22

Define critical volume

Answer 22

This is the volume occupied by one mole of a gas at its critical temperature and pressure

Question 23

Define critical point of a gas

Answer 23

The point on a phase diagram at which the gaseous state and liquid state become indistinguishable.