Chapter 19: Thermal Physics Flashcards

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1
Q

What are the conditions for energy transfer to take place?

A
  • one object exerts force on the other object and makes it move (work is done)
  • one object is hotter than another object, so energy transfer by heating takes place by means of conduction, convection or radiation (due to temperature difference)
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2
Q

What is internal energy?

A

The internal energy of an object is the sum of the random distribution of the kinetic and potential energies of its molecules.

The internal energy of an object is the energy of its molecules due to their individual movements and positions.

Sum of randomly distributed kinetic and potential energies of the particles in a substance

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3
Q

What is thermal energy?

A

The internal energy of an object due to its temperature is sometimes called thermal energy.

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4
Q

When does the internal energy of an object increase?

A

-Energy transfer occurs by heating the object

  • work is done on the object i.e by electricity
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5
Q

When does the internal energy of an object stay constant?

A
  • There is no energy transfer by heating, and no work is done
  • Energy transfer by heating and work done balance each other out
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6
Q

What does the first law off thermodynamics state?

A

When work is done or energy is transferred by heating to an object, the change of internal energy of the object - the total energy transfer due to work done and heating

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7
Q

What is a molecule?

A

The smallest particle of a pure substance that has characteristics of the substance.

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8
Q

What is an atom?

A

The smallest particle of an element that is characteristic of that element.

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9
Q

Describe molecules in a solid

A

The atoms and molecules are held tightly together due to the electrical charge of the protons and electrons in the atoms; the molecules in a solid vibrate randomly at fixed positions. The higher the temperature of the solid, the more the molecules vibrate. As energy is supplied, the kinetic energy of the molecules increases, causing them to vibrate so much that they break free from the solid structure and become free to move around; it has melted.

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10
Q

Describe molecules in a liquid

A

The molecules move about at random contact with each other; the forces are not strong enough to hold the molecules in fixed positions. The higher the temperature of a liquid, the faster its molecules move. When its temperature increases, the kinetic energy of the molecules causes the molecules tobreak free and move away from each other effectively vaapourising.

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11
Q

Describe molecules in a gas

A

The molecules move about randomly, but much further apart than a liquid, heating makes the molecule speed up and gain kinetic energy. the pressure increases. This means that they have more collisions with each other and the sides of the container and hence the pressure is increased.

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12
Q

What is temperature?

A

The degree of hotness of the object. The hotter the more internal energy it has

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13
Q

What is thermal equillibrium?

A

For any two objects that are at the same temperature, no overall energy transfer by heating will take place?

Energy is transferred from a region of high
temperature to a region of low temperature.

When two objects are in contact with each other
and they are of the same temperature , there is
no net transfer of energy between them.

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14
Q

What is a temperature scale?

A

These are fixed points, which are standard degrees of hotness that are accurately reproduced.

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15
Q

What is the celsius scale, and how is it defined?

A

unit celsius

It is defined based on boiling and freezing point of water

  • ice point 0° C, which is the temperature of pure melting ice.
  • Steam point is 100° C, which is the temperature of steam at standard atmospheric pressure.
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16
Q

What is the absolute scale, and how is it defined?

A

Kelvin scale SI unit

  • absolute zero 0K, which is the lowest possible temperature.
  • triple point of water, 273.16K, which is the temperature at which ice, water, and water vapour co-exist in thermodynamic equilibrium

ice point is 273.15 and steam point is 373.15

17
Q

What is the conversion from celsius to kelvin

A

temp in ° C = absolute temperature in K - 273.15

18
Q

What is absolute zero?

A

The lowest possible temperature with minimum internal energy regardless of the substances the object consists of.

19
Q

What is specific heat capacity?

A

Specific heat capacity c, The energy needed to raise the temperature of unit mass of the substance by 1K without change of state. The unit JKg-1K-1

ΔQ =mc(T2 - T1)

ΔQ = mcΔT

20
Q

What is the equation for the inversion tube experiment?

A

c = gLn/ΔT

mcΔT = mgLn

21
Q

How can the Specific heat capacity of metal be measured?

A

c = IVt/mΔT

22
Q

How can the Specific heat capacity of liquid be measured?

A

Assuming no heat loss to the surroundings.

IVt = m1c1ΔT + mcal ccal x ΔT

23
Q

What is the relationship between density and states?

A

The density of a gas is less than the same substance of a liquid or solid state; this is due to the fact that the molecules of a liquid and of a solid are packed together in contact with each other.

24
Q

why can’t solids flow?

A

The atoms in a solid are locked together by strong force bonds from which the atom is unable to break free from. In liquid or gas, the molecules have too much kinetic energy, and the force bonds are not strong enough to keep the molecules fixed to each other.

25
Q

What is the Latent heat of fusion?

A

The energy needed to change the state of unit mass to melt a solid at its melting point is called the latent heat of fusion.

When a solid is heated at its melting point, its atoms vibrate
so much that they break free from each other. The solid, therefore,
becomes a liquid due to energy being supplied at the melting point.

Latent heat is released when a liquid solidifies. This happens
because the liquid molecules slow down as the liquid cools until the
temperature decreases to the melting point. At the melting point,
the molecules move slowly enough for the force bonds to lock the
molecules together. Some of the latent heat released keeps the
temperature at the melting point until all the liquid has solidified.
· Latent means hidden. Latent heat supplied to melt a solid may
be thought of as hidden because no temperature change takes
place even though the solid is being heated.
. Fusion is a word used for the melting of a solid because the solid
fuses into a liquid as it melts.

26
Q

What is the latent heat of vapourisation?

A

The energy needed changes the state of unit mass to vaporize a liquid at its boiling point.

When a liquid is heated at its boiling point, the molecules gain
enough kinetic energy to overcome the bonds that hold them close
together. The molecules therefore break away from each other
to form bubbles of vapour in the liquid. The energy needed to
vaporise a liquid is called latent heat of vaporisation.

Latent heat is released when a vapour condenses. This happens
because the vapour molecules slow down as the vapour is cooled.
The molecules move slowly enough for the force bonds to pull the
molecules together to form a liquid.
Some solids vaporise directly when heated. This process is called
sublimation

27
Q

Does it require more energy to vaporise or melt a substance?

A

Vaporise

28
Q

What is the specific latent heat of fusion?

A

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

Q = ml

29
Q

What is the specific latent heat of vapourisation?

A

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

Q = ml

30
Q

Temperature - time graph

A

before the solid melts P = mcs (ΔT/Δt)s

Where (ΔT/Δt)s = P/mcs

after the solid melts P = mcL (ΔT/Δt)L

Where (ΔT/Δt)L = P/mcL

31
Q

When the temperature increases the amplitude of vibrations increase

A
32
Q

What is brownian motion

A

Brownian motion is the idea that very small objects have random motion in a liquid or gas due to random bombardment by the molecules in this substance.