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Physics > Molecules and Ideal Gases > Flashcards

Molecules and Ideal Gases Flashcards

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1
Q

what is the motion of molecules in a gas?

A

move quickly in any direction (random)

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2
Q

what did Brownian motion note about particles in a fluid?

A

particles in fluids move around continualy and bump into each other

collisions cause the particles to change direction and speed

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3
Q

what is absolute zero (give a value)?

A

0 Kelvin

(equivalent to -273oC)

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4
Q

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

A

absolute zero

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5
Q

what is kelvin temperature?

A

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

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6
Q

why is 0 Kelvin describes as absolute zero?

A

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

it cannot become less than this

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7
Q

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

A

-273oC

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8
Q

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

A

temperature in Kelvin = temperature in Celcius + 273

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9
Q

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

A

temperature in Celcius = temperature in Kelvin - 273

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10
Q

work out the Kelvin if Celcius = 0

A

273K

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11
Q

work out the Kelvin if Celcius = 100

A

373K

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12
Q

work out the Kelvin if Celcius = 39

A

312K

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13
Q

work out the Kelvin if Celcius = -200

A

73

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14
Q

work out the Kelvin if Celcius = -273

A

0K

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15
Q

work out the Celcius if Kelvin = 0

A

-273oC

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16
Q

work out the Celcius if Kelvin = 100

A

-173oC

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17
Q

work out the Celcius if Kelvin = 373

A

100oC

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18
Q

work out the Celcius if Kelvin = 300

A

27oC

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19
Q

work out the Celcius if Kelvin = 73

A

-200oC

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20
Q

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?

A

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

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21
Q

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?

A

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

22
Q

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?

A

the temperature would get higher

it would double (300K to 600K)

23
Q

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?

A

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

24
Q

define the pressure law

A

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

25
Q

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

A
26
Q

what apparatus is used to investigate the pressure law?

A

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’

27
Q

what is a water bath?

A

the combination of a heater and a container of water

28
Q

the pressure of a gas is …

A

the pressure of a gas is proportional to its Kelvin temperature

29
Q

what is the pressure law equation?

A

if V1 = V2 (constant) then P1 ÷ T1 = P2 ÷ T2

V = volume

P = pressure (Pa)

T = Kelvin

30
Q

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?

A

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

31
Q

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

A

P2 = P1 x (T2 ÷ T1)

32
Q

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?

A

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

33
Q

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

A

the gas particles move more slowly and the collisions are less hard and less frequent

this means that the pressure also decreases

34
Q

P1 = 100kPa

T1 = 20oC

T2 = 50oC

Calculate P2

A

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)

35
Q

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

A

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

36
Q

define Boyle’s Law

A

for a fixed mass of gas at a constant temperature, pressure is inveresly proportional to volume

p ∝ 1 ÷ V

p ∝ constant ÷ V

37
Q

rearrange p ∝ constant ÷ V to make constant the subject

A

constant = pV

38
Q

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

A

p ∝ constant ÷ V

constant = pV

= 5.0 x 105 x 0.02

= 10,000 Pa/m3

39
Q

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

A

p ∝ constant ÷ V

pressure = 10,000 ÷ 0.06

= 16666.7 Pa

40
Q

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

A

p ∝ constant ÷ V

V = constant ÷ p

= 10,000 ÷ 120,000

= 0.083m3

41
Q

draw a graph for Boyle’s law (P/V)

A

pressure is inversely proportional to volume

42
Q

draw a graph for Boyle’s law (P/ 1÷V)

A

pressure is inversely proportional to volume

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

43
Q

what is the equation for Boyle’s law?

A

when T1 = T2 then P1V1 = P2V2

T = temperature

P = pressure

V = volume

44
Q

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?

A

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

45
Q

rearrange P1V1 = P2V2 to make P2 the subject

A

P2 = P1V1 ÷ V2

46
Q

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

A

pressure law

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

47
Q

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

A

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

48
Q

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

A

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

49
Q

What is Brownian motion?

A

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

50
Q

What is Kelvin temperature proportional to?

A

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

Physics (24 decks)

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