Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Module 5 Physics > 5.1 > Flashcards

5.1 Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

Explain what is meant by thermal equilibrium?

A

Two bodies in thermal equilibrium have the same temperature and no net flow of thermal energy between them.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain how to convert degrees Celsius into kelvin.

A

Temperature in K=Temperature in °C+273 °C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain the difference between temperature and heat.

A

Temperature is a measure of the hotness of a substance, it is measured in °C or K. Heat is a measure of the thermal energy of a substance, it is measured in joules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What direction is the energy transfer?

A

High heat to low heat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define the triple point of water.

A

The triple point of water is defined as the temperature and pressure at which the three states of water (ice, water and steam) can exist at equilibrium. This is 273.16 K and 0.61 kPa.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Explain why the ‘absolute scale of temperature’ has this name.

A

The absolute scale of temperature, the kelvin, is not defined using the properties of any substance. It is defined using absolute zero – the lowest possible temperature which exists when a system has minimum energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain the importance of water in the Celsius scale of temperature.

A

The Celsius scale is defined by two fixed points – both of which use the properties of water:
The steam point – This is 100 °C. This is the temperature at which steam and liquid water are in
equilibrium at standard atmospheric pressure.
The ice point – This is 0 °C. This is the temperature at which ice and liquid water are in equilibrium at
standard atmospheric pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Convert 96 °C into kelvin.

A

Temperature in kelvin = 96 + 273 Temperature in kelvin = 369 K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Convert 203 K into Celsius.

A

Temperature in Celsius = 203 − 273 Temperature in Celsius = -70 °C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Convert 150 °C into K.

A

Temperature in kelvin = 150 + 273 Temperature in kelvin = 423 K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Compare solids, liquids and gases in terms of their spacing, order and motion.
Include a diagram in your answer.

A

Solids

The molecules are close to each other and vibrate around fixed positions in a random way. The molecules are regularly arranged in a 3D lattice structure. There are strong electrostatic attractions between molecules.

Liquids

The molecules are now free to move randomly but they are still in contact with other molecules and vibrating. There is only a weak attraction between the molecules.

Gases

The molecules are no longer in contact and move rapidly and randomly. The attraction between the molecules is negligible.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define internal energy.

A

Internal energy is the sum of the random distribution of kinetic and potential energies associated with the molecules of a system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe and explain what happens to the internal energy of a substance as the temperature decreases.

A

The internal energy will decrease. As the temperature decreases the particles vibrate less; this decreases the kinetic energy. As the internal energy is the sum of the kinetic and potential energies in a system, this decrease in kinetic energy decreases the internal energy.
Internal energy will not decrease to zero as electrostatic potential energy will always be stored in the particles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

State two factors that would
change the internal energy of a
system.

A
  • The input or removal of heat energy to or from the system.

- Doing work on the system, or the system doing work on the system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define absolute zero.

A

The temperature of a substance which has a minimum amount of internal energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

During a change in state from
gas to liquid explain what
happens to:

a) the temperature
b) the potential energy
c) the internal energy

A

a) The temperature stays constant. This is because all of the energy being removed from the system is being used to form forces of attraction between the gas molecules to change its state to liquid.
b) The potential energy decreases as the molecules are forming bonds and coming closer to each other.
c) The internal energy decreases. This is because the kinetic energy stays constant and the potential energy decreases. Internal energy is the sum of the potential and kinetic energies in a system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe Brownian motion, giving an example of it.

A

Brownian motion is the continuous random motion of small particles suspended in a fluid, visible under a microscope.

An example that shows Brownian motion is the motion of smoke particles in air or pollen grains in water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe what Brownian motion tells us about air molecules.

A

Air molecules are:

  • small (compared to smoke particles)
  • moving randomly
  • moving rapidly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Explain what causes Brownian motion.

A

Brownian motion is caused by the collisions of small particles with the particles of the fluid that contains them. These collisions are rapid, random and occur in all directions.
The net force on the particle determines the direction of motion of the particle.
At any given moment this net force may be in a different direction; this leads to the zigzag motion of the particles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Define the specific heat capacity.

A

The energy required to change the temperature of 1 kg of a substance by 1 K (or 1 °C).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

State an equation for the specific heat capacity.

State what each of the terms means.

A

E = mc∆θ

E − thermal energy
m − mass
c − specific heat capacity
∆θ − temperature change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Derive the units of specific heat

capacity.

A

E = mc∆θ

c =E/m∆θ
c =J/kg × K
c = Jkg^−1K^−1

Or
c = Jkg^-1°C^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

An object is heated up.

State three factors that the object’s temperature rise will depend on.

A

The material that the object is made of / the material’s specific heat capacity.
The mass of the object.
The thermal energy supplied to the object.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Define specific latent heat of fusion.

A

The specific latent heat of fusion is the energy required to change 1 kg of a solid into a liquid at constant temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Define specific latent heat of vaporisation.

A

The specific latent heat of vaporisation is the energy required to change 1 kg of a liquid into a gas at constant temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

State an equation for specific latent heat.

A

E = mL
E − energy transferred
m − mass
L − specific latent heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Describe an electrical experiment to measure the specific heat capacity of a substance.

State the apparatus needed, and the equations required to calculate the specific heat capacity.

A
  • Measure the mass of the substance using a balance.
  • Put an electrical heater into the substance.
  • Put a thermometer into the substance.
  • Connect a voltmeter and ammeter to the circuit containing the electrical heater.
  • Measure the temperature of the substance before heating.
  • Switch on the electrical heater.
  • Use a stopwatch to measure the heating time.
  • Turn off the electrical heater.
  • Measure the temperature of the substance after heating.

Use these equations to calculate the specific heat capacity:
Q = IVt
- If there are no energy losses:
IVt = mcΔθ
- Therefore, we can find the specific heat capacity using:
c =IVt/mΔθ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Calculate the energy required to increase the temperature of 7 kg of water from 20 °C to 90 °C.

The specific heat capacity of water is 4200 J kg^–1 K^–1.

A

Q = mcΔθ
Q = 7 × 4200 × 70 = 2 058 000 J
The energy required is 2 058 000 J.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Give an example of a time when the high heat capacity of water is an important property.

A

The body – 70% water content of the body ensures that the body remains at a constant temperature.
Coolant in power stations – useful in transferring energy.
Car radiator – useful in transferring energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Explain why calculating the specific heat capacity experimentally may give an inaccurate measurement of the specific heat capacity.

A
  • Heat loss to the surroundings
  • Heat loss to the apparatus
  • The substance may continue to heat up for a while after you finish timing
  • The substance may not heat up uniformly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Describe an electrical experiment to measure the latent heat of vaporisation of water.

A
  • Put water of a known mass into a double container, the inner container of which contains a small hole.
  • Submerge an electrical heater.
  • Connect an ammeter in series and a voltmeter in parallel to the electrical heater.
  • The electrical heater is turned on and some of the water begins to boil, turning to steam and escaping through the hole.
  • The water then condenses and is collected in a beaker.
  • The experiment is carried out over a time t; the time is measured using a stopwatch.
  • The mass of water evaporated and collected in the beaker is measured using a balance.
  • The voltage and current are measured using the voltmeter and ammeter.
We use the fact that: E = mLv 
and: E = VIt
to say: mLv = VIt
Therefore:
Lv = VIt/t
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Suggest some possible sources of error that would need to be taken into account when measuring the specific latent heat of fusion and of vaporisation of water.

A
  • The apparatus may heat up, need to take their specific heat capacity into consideration.
  • The water may continue to change state after the electrical heater is turned off – this can be improved by finishing timing when it stops changing state rather than when the heater is turned off.
  • The water remaining in the container will have heated up – need to take its specific heat capacity into consideration.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Explain the difference between the specific latent heat of fusion and the specific latent heat of vaporisation.

A

The specific latent heat of fusion is the energy required to change 1 kg of a solid into a liquid, whereas the specific latent heat of vaporisation is the energy required to change 1 kg of a liquid into a gas.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

2 kg of material X requires 3.2 kJ to change state from a solid to a liquid.

Calculate the specific latent heat of fusion of material X.

A 
Q = mL
L = Q/m = 3200/2 = 1600 J kg −1
35
Q

A 1 kg block of ice of temperature –5 °C was melted and heated to 70 °C.

Calculate the energy required.

cICE = 2200 J kg−1K−1
cWATER = 4180 J kg−1K−1
LfICE= 334 kJ kg−1
A

This question has three stages:
First find how much energy is needed to increase the temperature of ice from –5 °C to 0 °C.
Q = mcΔθ
Q = 1 × 2200 × 5 = 11 000 J

Now, find how much energy is need to change the state of solid ice to liquid water.
Q = mL
Q = 1 × 334 000 = 334 000 J

Finally, find how much energy is need to increase the temperature of water from 0 °C to 70 °C.
Q = mcΔθ
Q = 1 × 4180 × 70 = 292 600 J

Total energy required:
11 000 + 334 000 + 292 600 = 637 600 J

36
Q

State an equation that links pressure with the mean square speed.

State what each of the terms means.

A

pV =1/3NmCrms^2

p − pressure
V − volume
N − number of molecules
m − mass
c2̅ − mean square speed
37
Q

Explain what Avogadro’s constant tells us.

A

Avogadro’s constant tells us that there are 6.02x10^23 particles in one mole of a substance.

38
Q

State an equation to find the number of moles of a known substance given its mass.

A

n =m/Mr

n − number of moles
m − mass
Mr − molar mass (relative atomic/formula mass)

39
Q

State an equation to find the number of molecules in a substance given the number of moles.

A

N = nNA
N − number of molecules
n − number of moles
NA − Avogadro′s constant (6 × 1023 mol−1)

40
Q

Show that:

pV = NkT

A

We know that:
pV = nRT

and that:
k =R/NA

Combining these two equations:
R = kNA
pV = nNAkT

We also know that:
nNA = N
Finally:
pV = NkT

41
Q

Derive the equation:

1/2mc̅̅2̅ =3/2kT

A

We know that:
pV = NkT

and that:
pV =1/3Nmc̅̅2̅

Equating these two equations gives us:
NkT =1/3Nmc2̅

Cancel N:
kT =1/3mc2̅

Multiply each side by 3/2:
1/2mc̅̅2̅ =3/2kT

42
Q

Explain what is meant by the internal energy of an ideal gas.

A

The internal energy of an ideal gas is the sum of the mean kinetic energies of all the moleules in the gas.

For an ideal gas we assume potential energy is negligible (Ep=0), and so the internal energy is the sum of the mean kinetic energies.

43
Q

State Boyle’s law.

A

For a fixed mass of a gas at a constant temperature, pressure is inversely proportional to volume.

44
Q

What is the graph of P against V, at a constant temperature?

What does it look like at a higher temperature?

A

Inversely proportional.

Shift to the right.

45
Q

Define Pressure.

A

The force exerted per unit area.

46
Q

What causes pressure to be exerted in terms of Newtonian theory?

A

For a gas in a container, we assume that the gas particles will undergo perfectly elastic collisons with the walls of the container.

During the collisions, the particles have a change in momentum. By obeying Newton’s second law:
F=∆p/∆t

This means that the wall has exerted a force on the gas particle to cause this change in momentum.

Newton’s third law, which states that for every body that exerts a force, a force of equal magnitude and opposite direction is exerted back on that body. Therefore, as the wall of the container exerts a force on the gas particle, the gas particle also exerts a force on the walls of the container.

The force causes the pressure experienced on the walls of the container:
P= F/A

47
Q

What is meant by the absolute zero of temperature?

A

The temperature at which the particles have zero kinetic energy. This is the lowest possible temperature as 0 K on the kelvin scale.

48
Q

(Graph showing pV against Temperature, straight line through the origin)

What does the gradient tell us?

A

We know that:
pV = nRT

This can be compared to:
y = mx + c

Therefore,
gradient(m) = nR

49
Q

A gas ov volume 100cm^3, with constant pressure, expands to a volume of 200cm^3.

Given that the final temperature of the gas is 27C, calculate the intial temperature of the gas.

A

V/T = constant

V1/T1 = V2/T2

All temperature must be converted into kelvin and volumes into m^3

100 x 10^-6 / T1 = 200 x 10^-6 / 300

T1 = 150K

The initial temperature of the gas was 150K (-123C).

50
Q

A gas has a pressure of 6x10^4 Pa, a temperature of 30C and a volume of o.1m^3.

a) calculate the number of molecules in the gas.
b) Given that the gas is nitrogen gas N2, calculate the mass of the gas.

The molar mass of a nitrogen atom is 0.014kg.

A

pV = NkT

Convert temperatures to kelvin.
a)
N = pV/kT = (6x10^4x0.1)/(1.38x10^23 x 303) = 1.43 x 10^24 molecules

b) to find the number of moles n:

n = N/Na == (1.43 x 10^24)/(6.02x10^23) = 2.38 moles
n = m/Mr

Therefore, m =Mr x n = 0.028 x 2.38 = 0.067 kg

51
Q

A piston contains 0.5 m3 of air at a pressure of 7x104 Pa.

If the piston is compressed, decreasing the volume of air to 0.2 m^3, find the new pressure of the gas in the piston.

A

pV = constant
p1V1 = p2V2
7 × 10^4 × 0.5 = p2 × 0.2
p2 = 1.75 × 10^5 Pa

52
Q

Oxygen atoms have a molar mass of 0.016 kg.

a) Calculate the number of molecules in 5 moles of oxygen gas O2.
b) Calculate the mass of 5 moles of oxygen gas O2.

A

a)
N = n x NA
N = 5 × 6.02 × 10^23 = 3.01 × 10^ 24

b)
m = Mr x n
m = 0.032 × 5 = 0.16 kg

53
Q

State an equation for the Boltzmann constant.

A 
k = R / NA
where:
k − Boltzmann constant
R − gas constant
NA − Avogadro's constant
54
Q

Explain how an increase in temperature leads to an increase in pressure.

A
  • At higher temperatures, the molecules have more kinetic energy and move faster.
  • There is a larger change in momentum which causes a larger force.
  • The molecules have more frequent collisions with the walls of the container.
  • Pressure is force per unit area so the increase in force means an increase in the pressure.
55
Q

Describe a technique that could be used to demonstrate Boyle’s law.

A

Use a piston which has air trapped inside. Compress the piston using weights added to the top of the piston.

Vary the weights added and record the changes in volume of the gas in the piston.

Calculate the pressure using the fact that:
pressure = force / area

Plot a graph of pressure against 1/volume – the graph will show that the two values are directly proportional.

P = constant / V
PV = constant

Pressure is inversely proportional to volume (i.e. directly proportional to 1/volume).

56
Q

Describe a technique that could be used to demonstrate the pressure–temperature law.

A

Surround a gas container with water and connect it to a pressure gauge.

Increase the temperature of the water and measure the pressure.

Do this for a variety of different temperatures.

Plot a graph of pressure against temperature.

The graph will show that pressure is directly proportional to temperature.

Therefore:
P/T = constant

57
Q

Describe how a pressure vs temperature graph could be used to determine the value of absolute zero in Celsius.

A

Plot a graph with pressure on the y-axis and temperature in Celsius on the x-axis.

The point at which the line crosses the x-axis will give an approximate value of absolute zero in Celsius.

The point at which it crosses x = absolute zero, because absolute zero occurs when P = 0.

58
Q

Explain Boyle’s law in terms of the kinetic theory of gases.

A

When a gas is at a constant temperature, its pressure can be decreased by increasing its volume.

In a larger volume, the molecules of gas will travel further between collisions with the walls on the container. Therefore, there are fewer collisions per second – the pressure is less.

The reverse argument could also be given (a smaller volume increases the pressure as there will be more frequent collisions).

59
Q

State five assumptions of an ideal gas.

A
  1. Volume of the molecules is negligibly small compared to the volume of the gas.
  2. Molecules have elastic collisions (no energy losses with walls of container).
  3. There is a large number of molecules.
  4. Molecules move randomly.
  5. The time between collisions is much larger than the duration of collisions.
  6. There are no intermolecular forces.
60
Q

Explain how Newton’s laws are
used in the derivation of the
equation:

pV =1/3Nm(crms)^2

A derivation of the equation is
not required.

A

Newton’s first law tells us that a gas molecule will move in a straight line until it collides with the walls of the container.

Newton’s second law enables us to find the force on the molecule caused by its collision with the walls of the container.

Newton’s second law tells us that:

Force = change in momentum/ time

Newton’s third law tells us that the force exerted on the wall is equal and in an opposite direction to the force exerted on the molecule.

61
Q

Given that:
pV = 1/3 Nm(crms)^2

show that:
p = 1/3ρ(crms)^2

A

The total mass of a gas made up of N molecules of mass m is Nm.

The volume of the gas is V.

The density is:
Density =total mass / volume =Nm/V

Given that:
pV = 1/3Nm(crms)^2

Rearranging:
p = 1/3 x Nm/V x (crms)^2

Therefore:
p = 1/3ρ(crms)^2

62
Q

Calculate the temperature of a gas with an average kinetic energy of 5 × 10–22 J.

E = 1.38 × 10−23JK^−1

A

mean kinetic energy = 3/2kT

T = mean kinetic energy × 2 / 3k = (5 × 10^−22 × 2) /
(3 × 1.38 × 10^−23) = 24.15 K

63
Q

Calculate the root mean square speed of 3 moles of oxygen gas O2 with an average kinetic energy of 3.05 × 10–22 J.

The molar mass of oxygen gas O2 is 0.032 kg.

NA = 6.02 × 1023mol−1

A

mean kinetic energy = 1/2m(crms)^2

To find the mass of one molecule of gas, m:

m =Mass of gas/ Number of molecules in gas

=Mrn/Nan

=Mr/Na

m = 0.032 / 6.02 × 10^23 = 5.32 × 10−26 kg

Rearrange the first equation to get crms as the subject:

crms = √mean kinetic energy × 2 / m |

= √3.05 × 10^−22 × 2/5.32 × 10^−26 | = 107 m/s

64
Q

State the general characteristics of a Maxwell - Boltzmann distribution curve.

A

The area under the curve represents the total number of particles. This stays the same whatever the temperature.

If the curve has been normalised the area under the curve is equal to one. As temperature decreases, the peak of the curve will shift further to the left.

65
Q

(Maxwell Boltzmann curve of 800k)

sketch a curve for 200k

A

Peak shifted left (lower speed), taller, narrower,

66
Q

Why is the absolute scale used?

A

It doesn’t arbitrarily depend on the properties of a given substance (eg. water’s melting and boiling point for the Celsius scale).

0k (absolute zero) means that the particles have minimum internal energy.

67
Q

How does Brownian motion give evidence for the particle model of matter?

A

Smoke particles suspended in air can be seen to move randomly in all directions. This must be as a result of random collisions with particles making up the air.

68
Q

True or false: At a given temperature, all particles in a material have the same kinetic energy.

A

False. The kinetic energies will be randomly distributed around a central ‘most likely’ amount.

69
Q

How can you increase the thermal energy of a system?

A

We can increase it by heating it up or doing work on the object.

70
Q

Explain the energy changes that occur during a change of state.

A

During change of state the potential energy of the particles change but the kinetic energies don’t change.

71
Q

What equation can be used to determine the energy required to change the temperature of a substance?

A

Q = mcΔ𝜭

Where Q = energy, m = mass, c = specific heat capacity, Δ𝜭 = temperature change.

72
Q

Give the equation to work of the energy for change

of state?

A

Q=ml
Where Q = energy, m = mass, l = specific latent heat (‘of fusion’ if melting/freezing, ‘of vaporisation’ if condensing/evaporating)

73
Q

In an experiment to find ‘c’ for water, lots of energy input escapes to the surroundings. Will this lead to an over or underestimate of specific heat capacity?

A

● An overestimate.
● Specific heat capacity is calculated as: c = Q / mΔ𝜭
● The energy input will be used, but the temperature change of the water will be lower than it should be due to the escaped energy -
therefore c will be too high.

74
Q

What is an ideal gas?

A

A gas where:
● The gas molecules don’t interact with each other.
● The molecules are thought to be perfectly spheres.

75
Q

What is the ideal gas equation?

A

pV=nRT

Where p = pressure, V = volume, n = number of moles, R = the ideal gas constant, T = absolute temperature

76
Q

Assuming constant volume, how are the pressure and temperature of a gas related?

A

They’re directly proportional.

ie. P/T = constant

77
Q

Use the kinetic theory of gases to explain why a temperature increase leads to an increase in pressure.

A

● A temperature increase means the particles have more kinetic energy.
● More kinetic energy means a greater change in momentum during collisions with the container. There are also more frequent collisions.
● Change in momentum is proportional to force applied, and therefore to pressure as well.

78
Q

What equation links N, V, p, m and c?

A

pV = 1/3Nm(crms)^2

79
Q

What is meant by the root mean square speed?

A

The square root of the mean of the squares of the speeds of the molecules.

80
Q

What does the area under a Maxwell-Boltzmann curve represent?

A

The total number of particles.

81
Q

What are the units of the Boltzmann coefficient?

A

J/K

82
Q

The average kinetic energy of a particle in an ideal gas is equal to what?

A

1.5 kT

83
Q

True or false: ‘The internal energy of an ideal gas is proportional to absolute temperature’

A

True.
In an ideal gas there is no ‘potential energy’ component in the internal energy. This means the internal energy is proportional to the kinetic energy (which is, in turn, dependent on temperature).

Module 5 Physics (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions