Chapter 10 - Properties of Gases

Question 1

Gas

Answer 1

A substance that has no well-defined boundaries but diffuses rapidly to fill ant container in which it is placed

Question 2

Temperature

Answer 2

The measure of how hot or cold an object is

Question 3

What are the two scales used to measure temperature?

Answer 3

Celsius °C

Kelvin K

Question 4

What are the fixed points on the Celsius scale?

Answer 4

0°C and 100°C

Question 5

What is the fixed point on the Kelvin scale?

Answer 5

0K (absolute 0, i.e when a gas would occupy no volume

Question 6

State absolute 0 in Celsius and Kelvins

Answer 6

-273°C

0K

Question 7

State the freezing point of water in Celsius and Kelvins

Answer 7

0°C

273K

Question 8

State the boiling point of water in Celsius and Kelvins

Answer 8

100°C

373K

Question 9

Pressure (gas definition)

Answer 9

The force exerted by the gas on a unit area of its container

Question 10

What is the unit for pressure?

Answer 10

newtons per meter squared (N m⁻²)

a.k.a the Pascal (Pa)

(Pa is a very small unit so kilopascal (kPa) us also used)

Question 11

1 kPa = ….Pa

Answer 11

1 kPa = 1000 Pa

Question 12

What is normal atmospheric pressure?

Answer 12

1 x 10⁵ N m⁻² = 1 x 10⁵ Pa = 100 kPa

Question 13

How do you know the volume of a gas?

Answer 13

The volume of a gas is the same as the container it is held in

Question 14

What is the SI unit for volume?

Answer 14

cubic meter (m³)

Question 15

What other units do we use for volume?

Answer 15

cubic centimeters (cm³)
liters (L)
cubic decimeters (dm³)

1 liter = 1000cm³ = 1dm³

Question 16

What must we know in order to compare gases?

Answer 16

• temperature and pressure of the gas

- must be measured at the same temperature and pressure as each other

Question 17

What is standard temperature?

Answer 17

273K or 0°C (freezing point of water)

Question 18

What is standard pressure?

Answer 18

1 x 10⁵ Pa = 100 kPa

Question 19

Boyle’s Law

Answer 19

At a constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure

V ∝ 1/p

pV = k

Question 20

Explain the outcome of Boyle’s Law

Answer 20

When the volume of the container is decreased, the molecules of gas are moving in a smaller space and so will collide with each other more frequently, causing an increase in pressure

Question 21

Charles’ Law

Answer 21

At a constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale

V ∝ T (kelvin)

V/T = k

Question 22

Explain the outcome of Charles’ Law

Answer 22

As the molecules heat up, they have more kinetic energy to move around. They collide with each other and the container more frequently and, so as not to have an increase in pressure, the volume increases

Question 23

Combined Gas Law / General Gas Law

Answer 23

p₁V₁ p₂V₂
——- = ——–
T₁ T₂

Question 24

When is the Combined Gas Law / General Gas Law used?

Answer 24

In conversions of a gas from one set of conditions to another

Question 25

Gay-Lussac’s Law of Combining Volumes

Answer 25

In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in ratios of small whole numbers, provided that the volumes are measured at s.t.p

Question 26

Avogadro’s Law

Answer 26

Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure

Question 27

What is the consequence of Avogadro’s Law?

Answer 27

One mole of gas must have the same volume as one mole of any other gas, under the same conditions

Question 28

Molar volume

Answer 28

The volume occupied by one mole of a gas

Question 29

What is the volume of one mole of gas at s.t.p?

Answer 29

22.4L

Question 30

What is the volume of one mole of gas at room temperature?

Answer 30

24L

Question 31

Brownian Motion

Answer 31

The random movement of tiny particles suspended in a liquid or gas

Question 32

Volatile liquid

Answer 32

One with a low boiling point

Question 33

What are the possible points of error in the experiment to measure the relative molecular mass of a volatile liquid using a conical flask?

Answer 33

○ The lab balance is only accurate to one or two decimal placed
○ The graduated cylinder is not as accurate at measuring volume (as, say, a burette)
○ It is very difficult to cover the entire flask with the water. so the vapor may not be exactly the same temperature as the water
○ The outside of the flask may not be completely dry before reweighing

Question 34

What are the assumptions of the Kinetic Theory of Gases?

Answer 34

✔1. Gases consist of small particles in continuous motion
✘2. There are no attractive or repulsive forces between molecules of a gas
✘3. Gas molecules are so small that the actual volume is negligible compared with the space they occupy
?4. Collisions between molecules of a gas are perfectly elastic i.e there is no loss of kinetic energy
✔5. The kinetic energy of molecules in a gas is proportional to temperature measured on the kelvin scale

Question 35

Ideal gas

Answer 35

One that perfectly obeys all the assumptions of the Kinetic Theory of Gases under all conditions of temperature and pressure

Question 36

When do gases come closest to ideal gas behavior?

Answer 36

At low pressure and high temperature, when the particles are well separated

Question 37

Real gases

Answer 37

Real gases differ from ideal gases because:

i) forces of attraction do exist between molecules
ii) the volume of the molecules is not negligible

Question 38

What does the combination of Boyle’s, Charles’ and Avogadro’s Laws give?

Answer 38

Equation of State for an Ideal Gas

pV = nRT