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Thermal Physics Flashcards

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1
Q

What is internal energy of a body?

A

It is the ability to do work due to its state. It is the sum of a RANDOM DISTRIBUTION of kinetic and potential energies associated with its MOLECULES or atoms.

The work done by its stage is the ability to move(kinetic) or increase the energy of itself or other bodies(potential)

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2
Q

Using the definition, what is the equation of internal energy?

A

Internal energy = molecular kinetic energy Ek + molecular potential energy Ep

U = Ek + Ep

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3
Q

The internal energy of a body does not include the ______ of the body ______.

A

Energies of the body as a whole. E.g. Mechanical energies like kinetic energy due to the body’s motion or the potential energy.

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4
Q

Define the temperature of a body.

A

It is the average kinetic energy of it’s molecules or atoms.

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5
Q

When the temperature of a body rises, molecular kinetic energy and internal energy _____. Vice versa.

A

Increases.

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6
Q

What is heat?

A

It is the flow of internal energy between bodied of different temperature.

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7
Q

What is thermal contact?

A

When heat can flow between two bodies.

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8
Q

When two bodies are in thermal contact, how does heat flow?

A

From the body with the high temperature to the body with the one with the lower temperature.

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9
Q

What is thermal equilibrium?

A

It is when there is no net transfer of energy between two bodies. (The bodies are at the same temperature)

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10
Q

State the zeroth law of thermodynamics.

A

It suggests that a if bodies A and B are separately in thermal equilibrium with body C, then A and B are in thermal equilibrium with each other.

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11
Q

What are thermometer if properties?

A

They are physical properties which varies in a regular way with temperature.

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12
Q

What is the relationship between pressure, volume and temperature at pressures?

A

pV is proportional to T

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13
Q

What is a thermodynamic scale?

A

It is a temperature scale based on the relationship pV is proportional to T.

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14
Q

What is absolute zero on a thermodynamic scale?

A

It is the temperature at which all substances have a minimum internal energy.

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15
Q

What are fixed points in the Kelvin scale?

A

Absolute zero and triple point of water (where ice, water and water vapour exist in equilibrium because this point is invariant and reproducible) 273.16K

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16
Q

How is Celsius unit converted to Kelvin unit?

A

Celsius + 273.16 = Kelvin

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17
Q

What is specific heat capacity?

A

It is the amount of heat(or thermal energy) required to raise the temperature of unit mass by 1K without a change in state.

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18
Q

What is the formula for specific heat capacity?

A

Q=mc change in T

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19
Q

How is specific heat capacity determined using power?

A
  1. A known mass m of substance is used
  2. A known amount of heat is supplied to the substance with an electrical heater q = IVt
  3. Change in temperature is measured
  4. c is calculated from IVt = mc change in T
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20
Q

What is a caloriemeter?

A

It is an insulated vessel, where the experiment to determine heat capacity using power is carried out.

21
Q

What is specific latent heat of vaporisation/fusion and its equation?

A

lv/lf = q/m
Specific latent heat of vaporisation/fusion of a substance is the amount of heat needed to change unit mass of substance from liquid to gaseous/solid to liquid state with no change in temperature. SI unit: Jkg^-1

22
Q

What are the steps to determine latent heat using power?

A
  1. Heat is supplied to a substance with an electrical heater until it begins melting or boiling. q = IVt
  2. When the process in steady state, take the time taken to melt or boil the known mass of m.
  3. IVt = ml + h
  4. By carrying out the experiment twice, supplying different amount of heat (different I and/or V) in the same time t, the value of h is kept constant and can be eliminated.

I1V1t = m1l + h and I2V2 = m2l +h
==> l = (I1V1 - I2V2)t/(m1 - m2)

23
Q

What is the kinetic theory?

A

It states that all matter consists of particles in continuous random motion.

24
Q

What happens to the average speed and spacing of particles when heat is supplied to matter?

A

Both increase. When average kinetic energy increases, so it’s temperature rises. When average spacing increases, the average potential energy of its particles increases.

25
Q

How does melting occur?

A

At melting point, when heat is supplied to the object, the particles gain enough heat energy to overcome the strong intermolecular forces in the lattice structure.
As the solid melts, their potential energy increases as the space between the particles increase.
The kinetic energy(this the temperature) cannot increase because all further heat supplied is used to increase the potential energies of the particles.

26
Q

How does boiling occur?

A

When further hear is supplied at the boiling point, some particles will gain enough energy to overcome the intermolecular forces holding them.
As the particles become further apart, their potential energies increase.
Average kinetic energy of particles do not increase as heat supplied is used to overcome potential energies and increase potential energy.

27
Q

An increase in internal energy during melting or boiling is solely the increase in ______.

A

Average potential energy.

28
Q

Why is lv greater than lf? Explain using the first law of thermodynamics.

A

Both latent heats involve increasing molecular potential energy and doing work by the substance.

Latent heat of vaporisation is considerably greater because evaporation involves a considerably greater molecular separation and volume increase than melting.

Hence, it involves a considerably greater increase in average potential energy and more work has to be done by the system.

29
Q

What is evaporation?

A

It is a process where molecules of a liquid (or solid) escape from its surface, occurring at any temperature.

30
Q

Explain the process of evaporation and how it results in a cooling effect.

A

Particles of a liquid collide randomly, some largo less may attain higher kinetic energies. If it is moving in the upward direction near the surface, it may have enough kinetic energy to overcome the intermolecular forces and escape the surface of the liquid.

When particles of higher kinetic energies leave the liquid, particles of lower energies are left behind. And the average kinetic energy of the remaining parties would therefore be lower.

31
Q

What are the differences between evaporation and boiling?

A
  1. Evaporation occurs at the surface of the liquid while boiling occurs throughout the liquid.
  2. Evaporation occurs at any temperature while boiling only occurs at the boiling point.
32
Q

What is the first law of thermodynamics? What is the equation?

A

The increase in internal energy of a system is equal to the Sum of the heat q SUPPLIED to it and the work done ON it.

Change in U = q + w

33
Q

The first law of thermodynamics follows the concept of _____. This implied that energy is _____ from _____ for the internal energy to increase.

A

Conservation of energy, supplied, outside.

34
Q

Why is work done on a gas equals it -pressure x change in volume?

A

?

35
Q

How much is one mole of substance?

A

It is the amount of substance containing a number of particles equal to the Avogadro constant.

36
Q

What is Avogadro’s constant?

A

It is the number of atoms in 0.012kg of carbon-12 it has a value of 6.02 E23

37
Q

What is the ideal gas equation?

A

pV = nRT R is the molar constant.

38
Q

What is an ideal gas?

A

It is a gas that obeys pV = nRT.

39
Q

How to solve ideal gas questions?

A

Find what is constant and make the variables the subject of the ideal has equation. Equate the variables. Since n and R is usually constant, it can be omitted.

40
Q

What are the assumptions of the kinetic theory of gases?

A
  1. Molecules are of negligible size
  2. Molecules have negligible intermolecular forces of attraction
  3. Molecules are in continuous random motion
  4. All collisions between gas molecules are perfectly elastic.
41
Q

According to the kinetic theory of gases, what results in the gas pressure?

A

The collision of gas molecules with the walls of the container.

When a gas molecule collides with and rebounds from a wall, it undergoes a change in momentum indicating a force is exerted on the molecule by the wall (N2L) and an equal but opposite force is exerted on the wall by the molecule (N3L)

Continuous random collisions by all molecules of gas would average out to a steady force on the walls.

p = F/A so pressure is exerted on the walls.

42
Q

Use the kinetic gas theory to derive the equation pV = 1/3 Nm

A

N molecules with mass m and mean square speed exert a pressure of 1/3 Nm / V . (Why?)

43
Q

Explain how nRT = Nkt.

A

k = Boltzmann constant = R/ Avogadro’s constant (JK^-1)

44
Q

Obtain the formula for the average translational kinetic energy.

A

Combining the ideal gas equation and the kinetic theory of gases, 1/3 Nm = NkT m = 3/2 kT

= 1/2 m = 3/2 kT t

45
Q

Derive the internal energy equation of an ideal gas.

A

In an ideal gas, the intermolecular forces are negligible as the particles are very far apart. PE is 0, U = sum of KE of all particles = Sum of 3/2 kT. Thus U = 3/2 Nkt = 3/2nRT.

46
Q

Combining the first law of thermodynamics and the equation of the internal energy equation, find the relationship between q + w and T. What does this imply when a fixed mass of ideal gas is compressed?

A

U = q + W = 3/2 NkT = 3/2 nRT

U = q + w is proportional go temperature.

q is work done. When the gas is compressed, q increases. So G will rise.

47
Q

In a p against v graph, what is the sum of the internal energies?

A
  1. Vectors!
48
Q

How can the ideal gas equation be used to find density and Mr?

A

n = m/M rho= m/V

pV = nRT = m/M RT M= m/V RT/p

Physics (12 decks)

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