Molecules and Ideal Gases

Question 1

what is the motion of molecules in a gas?

Answer 1

move quickly in any direction (random)

Question 2

what did Brownian motion note about particles in a fluid?

Answer 2

particles in fluids move around continualy and bump into each other

collisions cause the particles to change direction and speed

Question 3

what is absolute zero (give a value)?

Answer 3

0 Kelvin

(equivalent to -273^oC)

Question 4

what is the temperature below which it is not possible to cool a gas further?

Answer 4

absolute zero

Question 5

what is kelvin temperature?

Answer 5

kelvin temperature is proportional to the average kinetic energy of its molecules

Question 6

why is 0 Kelvin describes as absolute zero?

Answer 6

because the pressure of a gas is 0 when cooled to 0K

it cannot become less than this

Question 7

what is the Celcius equivalent to absolute zero (0K)

Answer 7

-273^oC

Question 8

how do you work out the temperature in Kelvin given the Celcius temperature?

Answer 8

temperature in Kelvin = temperature in Celcius + 273

Question 9

how do you work out the temperature in Celcius given the Kelvin temperature?

Answer 9

temperature in Celcius = temperature in Kelvin - 273

Question 10

work out the Kelvin if Celcius = 0

Answer 10

273K

Question 11

work out the Kelvin if Celcius = 100

Answer 11

373K

Question 12

work out the Kelvin if Celcius = 39

Answer 12

312K

Question 13

work out the Kelvin if Celcius = -200

Answer 13

73

Question 14

work out the Kelvin if Celcius = -273

Answer 14

0K

Question 15

work out the Celcius if Kelvin = 0

Answer 15

-273^oC

Question 16

work out the Celcius if Kelvin = 100

Answer 16

-173^oC

Question 17

work out the Celcius if Kelvin = 373

Answer 17

100^oC

Question 18

work out the Celcius if Kelvin = 300

Answer 18

27^oC

Question 19

work out the Celcius if Kelvin = 73

Answer 19

-200^oC

Question 20

A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the volume of the gas?

Answer 20

the volume becomes larger as the particles move more so there is more space between them

Question 21

A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the pressure of the gas?

Answer 21

the pressure would get higher as the particles would collide more often

Question 22

A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the temperature of the gas?

Answer 22

the temperature would get higher

it would double (300K to 600K)

Question 23

A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the speed of the molecules of the gas?

Answer 23

the speed of the molecules would increase as the particles have more kinetic energy (converted from thermal energy)

Question 24

define the pressure law

Answer 24

for a fixed mass of gas at a constant volume, temperature (measured in Kelvin) is directly proportional to pressure

P ∝ Temperature (Kelvin)

or P = constant x T

P/T = constant

Question 25

draw a diagram for the apparatus used in an investigation about pressure law

Answer 25

Question 26

what apparatus is used to investigate the pressure law?

Answer 26

iced water pressure sensor data logger temperature sensor computer electric heater round bottom flask 'ideal' gas (air) note: the combination of a heater and a container of water is known as a 'heat bath'

Question 27

what is a water bath?

Answer 27

the combination of a heater and a container of water

Question 28

the pressure of a gas is **...**

Answer 28

the pressure of a gas is **proportional to its Kelvin temperature**

Question 29

what is the pressure law equation?

Answer 29

if V₁ = V₂ (constant) then P₁ ÷ T₁ = P₂ ÷ T₂ V = volume P = pressure (Pa) T = Kelvin

Question 30

A gas is trapped inside a container with a fixed size (its volume cannot change). What will happen to the gas and pressure if it is heated?

Answer 30

the particles will gain kinetic energy which will make them move faster this means they will collide with each other and the walls more frequently per second this causes the force on the walls of the container to increase and so the pressure increases

Question 31

rearrange the pressure equation P₁ ÷ T₁ = P₂ ÷ T₂ so P₂ is the subject

Answer 31

P₂ = P₁ x (T₂ ÷ T₁)

Question 32

A car tyre contains air at 1.25 × 10⁵ Pa when at a temperature of 27°C. Once the car has been running for a while the temperature of the air in the tyre rises to 42°C. If the volume of the tyre does not change what is the new pressure of the air in the tyre?

Answer 32

First convert the temperatures into kelvin: T₁ = 27 + 273 = 300K, T₂ = 42 + 273 = 315K Now calculate the new pressure: P₁ ÷ T₁ = P₂ ÷ T₂ so P₂ = P₁ x (T₂ ÷ T₁) P₂ = 1.25 x 10⁵ x (315 ÷ 300) P₂ = 131250 Pa = new pressure of the air in the tyre

Question 33

what happens to the particles in a gas when the temperature is decreased?

Answer 33

the gas particles move more slowly and the collisions are less hard and less frequent this means that the pressure also decreases

Question 34

P₁ = 100kPa T₁ = 20^oC T₂ = 50^oC Calculate P₂

Answer 34

First convert the temperatures into kelvin: T₁ = 20 + 273 = 293, T₂ = 50 + 273 = 323K Now calculate the new pressure: P₁ ÷ T₁ = P₂ ÷ T₂ so P₂ = P₁ x (T₂ ÷ T₁) P₂ = 100kPa x (323 ÷ 293) P₂ = 110.24kPa (2 d.p)

Question 35

Explain how the motion of particles exert a pressure on the walls of a container referring to force and collisions

Answer 35

the particles in a gas move quickly in all directions and collide with each other and the walls of their container when gas particles hit the walls of their container they exert a tiny force the more collisions per second the greater the exerted force and thus a greater pressure

Question 36

define Boyle’s Law

Answer 36

for a fixed mass of gas at a constant temperature, pressure is inveresly proportional to volume p ∝ 1 ÷ V p ∝ constant ÷ V

Question 37

rearrange p ∝ constant ÷ V to make constant the subject

Answer 37

constant = pV

Question 38

if the volume is 0.02m³ and the pressure is 5.0 x 10⁵Pa, calculate the constant

Answer 38

p ∝ constant ÷ V constant = pV = 5.0 x 10⁵ x 0.02 = 10,000 Pa/m³

Question 39

given that the constant is 10,000 and the volume is 0.06m³, calculate the pressure

Answer 39

p ∝ constant ÷ V pressure = 10,000 ÷ 0.06 = 16666.7 Pa

Question 40

given that the constant is 10,000 and the pressure is 1.2 x 10⁵ Pa, calculate the volume

Answer 40

p ∝ constant ÷ V V = constant ÷ p = 10,000 ÷ 120,000 = 0.083m³

Question 41

draw a graph for Boyle's law (P/V)

Answer 41

pressure is inversely proportional to volume

Question 42

draw a graph for Boyle's law (P/ 1÷V)

Answer 42

pressure is inversely proportional to volume (inverse is on x-axis so line is directly proportional - straight line through the origin)

Question 43

what is the equation for Boyle's law?

Answer 43

when T₁ = T₂ then P₁V₁ = P₂V₂ T = temperature P = pressure V = volume

Question 44

A sealed syringe contains 10 x10^-6 m³ of air at 1 × 10⁵ Pa. The plunger is pushed until the volume of trapped air is 4 x 10^-6 m³. If there is no change in temperature what is the new pressure of the gas?

Answer 44

P₁ = 1 × 10⁵ Pa V₁ = 10 x10^-6 m³ V₂ = 4 x 10^-6 m³ P₁V₁ = P₂V₂ P₂ = P₁V₁ ÷ V₂ = (1 × 10⁵ x 10 x10^-6) ÷ 4 x 10^-6 m³ = 2.5 × 10⁵ Pa

Question 45

rearrange P₁V₁ = P₂V₂ to make P₂ the subject

Answer 45

P₂ = P₁V₁ ÷ V₂

Question 46

describe the relationship between pressure and temperature for a fixed mass of gas at a constant volume

Answer 46

pressure law the pressure of the gas is directly proportional to the Kelvin temperature of the gas

Question 47

is it safer to leave scuba tanks in the hot sun or in water? why?

Answer 47

it is safer in the water left in the hot sun, the tanks will get ot and the pressure will increase because the gas expands - the tanks could explode left in the water, tanks are cooler because water has a high heat capacity - the tanks are safe

Question 48

explain using a gas law what you would expect to happen to a bubble released by a SCUBA diver as it rises to the surface you may assume that the temperature of the gas does not change

Answer 48

because the mass and temperature are constant, the pressure will decrease because as the bubble rises, pressure decreases therefore, the volume will increase because Boyle's law states that pressure and volume are inversely proportional for a fixed mass of gas at a constant temperature

Question 49

What is Brownian motion?

Answer 49

particles move in zigzap, random motion this type of movement of any particles in a suspension is known as Brownina motion large, heavy particles (e.g. smoke) can be mved by Brownian motion by smaller, lighter particles (e.g. air) travelling at high speeds - which is why smoke particles in air appear to move around randomly when you observe them in the lab

Question 50

What is Kelvin temperature proportional to?

Answer 50

Kelvin temperature is proprotional to the average kinetic energy of the molecule of gas