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Thermal Physics > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

When does energy transfer occur? How does internal energy increase?

A

When one object does work on the other object, or when one object is hotter than the other, resulting in energy transfer by heating due to a temperature difference.

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2
Q

What is the first law of thermodynamics?

A

The total change of the internal energy of an object is equal to the total energy transfer due to work done and heating.

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3
Q

What is the definition of internal energy?

A

The sum of the random distributions of kinetic and potential energies of the molecules.

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4
Q

What is the meaning of temperature?

A

It measures the degree of hotness an object has

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5
Q

When is thermal equilibrium attained?

A

When two objects are at the same temperature.

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6
Q

What is absolute zero?

A

Zero kelvin. Minimum internal energy

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7
Q

What is degrees to kelvin change?

A

+273.

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8
Q

What is the specific heat capacity of a substance?

A

The energy needed to raise the temperature of a unit mass of the substance by 1k without change of state.

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9
Q

what is the unit of c (specific heat capcacity )

A

JKG^-1K^-1

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10
Q

What energy transfer occurs in an inversion tube?

A

Potential energy is converted into internal energy when it hits the bottom of the tube.

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11
Q

What is the specific latent heat of fusion?

A

The energy needed to change the state of a unit mass of substance from solid to liquid without change of temperature.

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12
Q

What is the specific latent heat of vaporisation?

A

The energy needed to change the state of a unit mass of substance from liquid to vapour without change of temperature.

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13
Q

What is the meaning of the term ‘latent’

A

Hidden

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14
Q

What is latent heat of fusion?

A

The energy needed to melt a solid at its melting point

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15
Q

What is latent heat of vaporisation?

A

The energy needed to vaporise a liquid at its boiling point.

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16
Q

What is the name of the process of a solid turning directly into a gas?

A

Sublimation

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17
Q

What are the energy changes during heating and melting?

A

During heating, particles gain kinetic energy, however during melting, temperature doesn’t change, so particles are gaining potential energy.

18
Q

Which formula should be used to find latent heat of fusion or vaporisation?

A

Q=ML. L = specific latent heat of fusion/vaporisation.

19
Q

What is Boyle’s law?

A

PV = constant.

20
Q

What is charles’ law?

A

V/T = constant.

21
Q

What is the pressure law?

A

P/T = constant.

22
Q

What is work done to change volume of a gas formula?

A

W = PV.

23
Q

How were the gas laws discovered originally?

A

By experiment rather than by theory.

24
Q

What is brownian motion?

A

The irregular motion of small particles suspended in a liquid or a gas, caused by the bombardment of the particles by molecules in the medium.

25
Q

What is avogadro’s constant?

A

The number of atoms in exactly 12g of carbon-12 isotope.

26
Q

What is a mole?

A

An amount of substance that contains Na particles (Avogadro number)

27
Q

What is the definition of an ideal gas?

A

A gas that obeys Boyle’s law.

28
Q

What is the ideal gas equation?

A

PV = nRT. n = number of moles of substance. Also written as PV = NkT.

29
Q

What is the theoretical explanation for Boyle’s law?

A

Pressure increases when volume decreases because gas molecules travel less distance between impacts at walls. This leads to more impacts per second, and pressure is therefore greater.

30
Q

What is the explanation for the pressure law?

A

Average speed of the molecules is increased by raising the temperature. Impacts on the container walls are harder and more frequent, so pressure is increased.

31
Q

What happens to velocity vs number of molecules graph when temperature of gas is raised?

A

Molecules move faster on average, due to higher kinetic energy, so the root mean square speed increases. Curve becomes flatter and broader because the greater the temperature, the more molecules are moving at higher speeds. Peak is slightly lower and more to the right.

32
Q

What are the assumptions made in kinetic theory of gases?

A

Molecules are point molecules - their volume is negligible.

Molecules don’t attract each other - this would reduce the force of their impacts on container surface.

Molecules move in continual random motion

Elastic collisions only

Duration of collisions is very short compared to time spent between collisions.

All molecules of gas are identical

33
Q

Difference between heat and temperature?

A

Heat is a measure of energy. When you heat an object you are transferring energy to it by there being a temperature difference.

34
Q

Why is there no change in temperature during melting/evaporation.

A

During state changes, energy is used to break bonds, not raise the temperature.

35
Q

How do you answer questions involving two objects transferring thermal energy between each other, and one is melting, for example ice in water which is melting

A

Equate shc energy formula of water including its temperature change to that of the ice, but add on latent heat of fusion to equation on rhs. Use the fact that they will both reach the same temperature in the end. One equation in terms of T (final temperature) should be written.

36
Q

What is difference between ideal gas and perfect gas?

A

Ideal gas obeys boyle’s law whereas a perfect gas almost obeys boyle’s law.

37
Q

What is difference between kelvin and degrees scale?

A

Kelvin is an absolute scale which starts at zero. Degrees is a relative scale.

38
Q

What is isobaric and what is isothermic?

A

Constant pressure and constant temperature.

39
Q

How do you get the mass of a molecule?

A

Mass of one mole / Avogadro’s constant.

40
Q

Why is it a MEAN kinetic energy?

A

Motion of the particles is random, so each kinetic energy will be different.

Thermal Physics (1 decks)

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