Gaseous State

Question 1

What are the assumptions for kinetic theory?

Answer 1

• gas particles are in constant random motion
  *** gas particles have negligible volume compared to the volume of the container
• gas particles exert negligible intermolecular forces on one another**
• collisions between gas particles are perfectly elastic
• average kinetic energy of particles is directly proportional to absolute temperature

Question 2

What does the pressure of gas depend on?

Answer 2

• frequency of collisions
• speed at which particles are colliding against the wall

Question 3

What is the pressure on earth at sea level?

Answer 3

• 1atm = 101325Pa or Nm⁻²
• 760mm Hg

Question 4

How to convert dm³ to m³?

Answer 4

1dm³ = 10⁻³ m³

Question 5

How to convert cm³ to m³?

Answer 5

1cm³ = 10⁻⁶ m³

Question 6

How to convert 1 bar to 1Pa?

Answer 6

1 bar = 100 000Pa

Question 7

What is Boyle’s law?

Answer 7

• At constant temperature, the volume of a fixed volume of gas is inversely proportional to its pressure
• V ∝ 1/p
• pV = constant, p1V1 = p2V2

Question 8

What does the V against p graph of a fixed mass of gas at constant temperature look like?

Answer 8

• curve downward sloping with decreasing gradient
• 1/x graph

Question 9

What does v against 1/p graph look like for a fixed mass of gas at constant temperature?

Answer 9

straight line that passes through origin

Question 10

What does pV against p graph look like for a fixed mass of gas at constant temperature?

Answer 10

horizontal straight line

Question 11

What is Charles’ law?

Answer 11

• At constant pressure, the volume of a fixed mass of gas is directly proportional to the absolute temperature
• V ∝ T
• V/T = constant, V1/T1 = V2/T2

Question 12

What does a V against T (in K) graph for a fixed mass of gas at constant pressure look like?

Answer 12

straight line that passes through origin

Question 13

What does a V against T (in °C) graph for a fixed mass of gas at constant pressure look like?

Answer 13

Straight line with x-intercept at -273°C

Question 14

What is Avogadro’s law?

Answer 14

• At constant temperature and pressure, the volume of gas is directly proportional to the number of moles of the gas
• V ∝ n
• V/n = constant, V1/n1 = V2/n2

Question 15

What is partial pressure?

Answer 15

Pressure that the gas would exert as if it occupied the container alone under the same conditions

Question 16

What is Dalton’s law of partial pressure?

Answer 16

The total pressure of a mixture of non-reacting gases equals the sum of partial pressures exerted by constituent gases

Question 17

What is Dalton’s law of partial pressure’s formula?

Answer 17

P(total) = Pa + Pb + Pc + …

Question 18

What is the formula for partial pressure?

Answer 18

pₐ = (nₐ/nₜₒₜₐₗ) × pₜₒₜₐₗ

Question 19

How do we know if a gas is “ideal”?

Answer 19

For 1 mol of ideal gas, n=pV/RT = 1 at all pressures

Question 20

At what condtions do real gas deviate more from ideal behaviour?

Answer 20

• high pressures
• low temperatures

Question 21

What kind of gas particles deviate more from ideal gas behaviour and why?

Answer 21

• large electron cloud
• polar

Question 22

How does gas particles with large electron cloud affect their ideal behaviour?

Answer 22

• strength (due to larger number of electrons) and extensiveness (due to larger surface area) of intermolecular forces between gas particles would be more significant
• volume of larger gas particles would be more significant when compared to the volume of the container

Question 23

How do polar molecules affect their ideal gas behaviour?

Answer 23

intermolecular forces (pd-pd or hydrogen bonding) would be stronger compared to weaker id-id between non-polar molecules of similar Mr

Question 24

Under what conditons do real gas approach ideal behaviour?

Answer 24

• low pressure
• high temperature

Question 25

Why does a real gas approach ideal behaviour at low pressure and high temperature?

Answer 25

• At low pressure, gas occupies a large volume and thus the volume of gas particles is negligible compared to the volume of the container, intermolecular forces of attraction would also be negligible as the particles are far apart
• At high temperature, particles have high kinetic energy and hence have sufficient energy to overcome the intermolecular forces of attraction

Question 26

Why is there differing speed for gas particles?

consider what happens at same temperature

Answer 26

• at the same temperature, all particles in a sample of gas have the same kinetic energy and hence average speed but the individual particles do not have the same speed
• due to collisions (between particles and wall of container), there will be a large range of speed at any given moment in a sample of gas

Question 27

What does the area under the curve for Maxwell-Boltzmann distribution represent?

Answer 27

total number of gas particles

Question 28

What does peak of each curve of Maxwell Boltzmann distribution curve represent?

Answer 28

most probable speed, v or most probable energy, E

Question 29

What happens to the Maxwell-Boltzmann distribution curve when temperature increases?

Answer 29

• peak of the curve shifts right (most probable speed increases)
• curve flattens (more particles have high energy and less have low energy)
• area under the curve is same for total number of particles is the same

Question 30

What is the axis of Maxwell-Boltzmann distribution curve?

Answer 30

• y-axis: Number of particles with energy, E
• x-axis: speed (or energy)

Question 30

What does the distribution of speed in Maxwell-Boltzmann distribution curve depend on?

Answer 30

• temperature
• mass of particle

Question 31

How does mass of particle affect the Maxwell-Boltzmann distribution curve?

Answer 31

• particles with lower masses have higher average speed
• most probable speed (peak will be higher)