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CGP PHYSICS > Chapter 13 - gas laws > Flashcards

Chapter 13 - gas laws Flashcards

1
Q

What is the lowest possible temperature called?

A

Absolute zero

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2
Q

What are the units of the absolute temperature scale?

A

Kelvin

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3
Q

What is absolute zero in kelvin?

A

0K

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4
Q

What is absolute zero in °C?

A

-273°C

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5
Q

What is the symbol for kelvin?

A

K

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6
Q

What is the kinetic energy of particles at zero kelvin?

A

The minimum possible energy

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7
Q

What does a change of one K equal in °C?

A

A change of one °C

one degree in kelvin = one degree in °C

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8
Q

What units do all equations in thermal physics use?

A

kelvin, K

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9
Q

How do you convert from °C to kelvin?

A

Add 273

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10
Q

How do you convert from kelvin to °C?

A

subtract 273

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11
Q

What is Boyle’s law?

A

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

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12
Q

What is Charles’ law?

A

At a constant pressure, the volume of a gas is directly proportional to its absolute teperature

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13
Q

What is the pressure law?

A

At a constant volume, the pressure of a gas is directly proportional to its absolute temperature

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14
Q

What are the three gas laws as equations?

A 
p = k/V
V = kT
p = kT
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15
Q

What is the ideal gas equation?

A

pV = nRT

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16
Q

When does a real gas approximate an ideal gas (so that the ideal gas equation can be used) ?

A

At low pressure and high temperature

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17
Q

What is the amount of gas measured in?

A

moles

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18
Q

What is the symbol for number of moles?

A

n

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19
Q

What is R?

A

The molar gas constant

8.31

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20
Q

What are the units of the molar gas constant?

A

Jmol^-1K^-1

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21
Q

What is k?

A

Boltzmann’s constant

1.38 x10^-23

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22
Q

What are the units of Boltzmann’s constant, K?

A

JK^-1

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23
Q

How could Boltzmann’s constant be described?

A

The molar gas constant for one particle of gas

as R is the gas constant for one mole of gas

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24
Q

What is Boltzmann’s constant equivalent to?

A

R/NA

NA = avagadro’s number

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25
Q

What is Avagadro’s number?

A

The number of particles in one mole of gas

6.02 x10^23

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26
Q

What is the symbol for Avagadro’s number?

A

NA

with subscript A

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27
Q

What is N?

A

The number of particles in a particular mass of gas

28
Q

What is the equation for the number of particles in a mass of gas?

A

N = nNa

number of moles x avagadro’s number

29
Q

What is the equation of state?

A

pV = NKT

30
Q

What is kinetic theory used for?

A

Explaining the gas laws on a microscopic level by modelling particles as hard balls which obey Newton’s laws

31
Q

Why is particle velocity proportional to pressure?

A

A faster particle has a larger momentum
A larger momentum means a larger impulse force on the wall
pressure is proportional to force, so pressure is greater
+ a higher velocity means less time taken to travel across the container, so more collisions and more force total

32
Q

Why is number of particles, N, proportional to pressure?

A

More particles means more collisions, so a greater total force and a greater pressure

33
Q

Why is the volume of the container inversely proportional to pressure?

A

A smaller container means less distance to travel between the walls, so a shorter travel time and more collisions
More collisions per second means a larger total force and a greater pressure
+ a lower volume means sides have a lower area. pressure = force/area so the same force on a smaller area means a greater pressure

34
Q

How do gas particles travel?

A

In random directions at different speeds

35
Q

How many particles can be estimated to be travelling in one dimension (x/y/z) at any given time?

A

a third

36
Q

What is the mean square speed?

A

The mean average of the squares of the velocities

37
Q

How is mean square speed represented?

A

c^2 with a bar on top

38
Q

What is the gas equation using mean square speed?

What does m represent in this equation?

A 
pV = 1/3Nm(mean square speed)
m = the mass of one particle
39
Q

What is the root mean square speed?

A

The typical speed of particles

the root of the mean of the squared velocities

40
Q

How is root mean speed commonly written?

A

r.m.s speed

41
Q

What are the units of the mean square speed?

A

m^2s^-2

42
Q

What are the seven assumptions made about gases in kinetic theory?

A
  • There is a large number of particles
  • Particle move rapidly and randomly (no preferential motion, no fields)
  • Particles obey Newton’s laws
  • Collisions between particles and walls are, on average, perfectly elastic
  • No attractive forces between particles
  • Any forces which act during collisions are instantaneous
  • Particles have a negligible volume compared to the volume of the container
43
Q

What is a gas which obeys all assumptions called?

A

An ideal gas

44
Q

How is the motion of a single gas particle modeled?

A

With a RANDOM WALK

The particle starts in one place, moves N steps in random directions, and ends up somewhere else

45
Q

What causes a particle to change direction during a random walk?

A

collisions with other particles

46
Q

What is the distance moved on a random walk proportional to?

A

the square root of the total number of steps

47
Q

What is the symbol for the number of steps in a random walk?

A

N

48
Q

How far can a gas particle usually move per step of a random walk (ie distance traveled between collisions)?

A

10^-7 m

49
Q

What is the thermodynamic scale?

A

The temperature scale in kelvin

50
Q

From what regions is thermal energy transferred to and from?

A

Always from areas of higher thermal energy to areas of lower thermal energy

51
Q

When will the exchange of thermal energy stop?

A

When thermal equilibrium is reached

All regions have the same thermal energy (all at the same temperature) so the net flow of energy stops

52
Q

What is a rule of thermal equilibrium?

A

If body A and body B are in thermal equilibrium with body C, then body A and body B must be in thermal equilibrium with each other

53
Q

What is specific thermal capacity?

A

The amount of energy needed to raise 1kg of a substance by 1K

54
Q

What is the symbol for specific thermal capacity?

A

c

55
Q

What is the formula for change in thermal energy?

A

energy change = mass x specific thermal capacity x change in temperature
ΔE = mcΔθ

56
Q

What is Δθ?

A

Change in temperature in K or °C

57
Q

What are the units of c?

A

Jkg^-1K^-1 or Jkg^-1°C^-1

58
Q

What does the speed distribution of gas particles depend on?

A

The temperature of the gas

59
Q

What happens to the speed of gas particles as the temperature increases?

A
  • Average particle speed increases
  • maximum particle speed increases
  • The speed distribution curve becomes more spread out (flatter)
60
Q

What is internal energy?

A

The total energy of a system

61
Q

What is the formula for internal energy?

A

kinetic energy of particle + potential energy of particles

62
Q

How is total kinetic energy of particles in a gas found?

A

Taking the average kinetic energy and multiplying it by the number of particles

63
Q

What is the formula for the average kinetic energy of an individual particle in a gas?

A

1/2m(mean square speed)

1/2 x m x v^2

64
Q

What is the equation for the average kinetic energy of a gas particle?

A

1/2m(mean square speed) = 3nRT/2N

65
Q

What affect on the energy will a rise in absolute temperature have on a gas?

A

The kinetic energy will increase and so the internal (total) energy will increase

CGP PHYSICS (8 decks)

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