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Heat and Temperature
Temperature – measure of the average kinetic
energy of molecules making up an object
Heat – energy in transit from one body to
another because of the difference in
temperature; it is the measure of the total
kinetic energy of the particles of a body;
SI Unit: joule (J) and calorie (cal)
Heat
Calorie – amount of heat needed to change
the temperature of one gram of water from
14.5OC to 15.5OC at a pressure of 1 atm
1 calorie = 4.186 joules
Mechanical equivalent of heat
– the ratio 4.186 J/cal
Temperature Scales
Ice point – temperature at
which ice melts under
pressure of 1 atm
Steam point – temperature
at which water boils
under a pressure of 1 atm
Temperature Scales
1. Celsius and Fahrenheit Scales
𝑻𝑪 =
𝟓
𝟗
(𝑻𝑭 − 𝟑𝟐) 𝑻𝑭 =
𝟗
𝟓
𝑻𝑪 + 𝟑𝟐
2. Kelvin Scale
𝑻𝑲 = 𝑻𝑪 + 𝟐𝟕𝟑
3. Rankine Scale
𝑻𝑹 = 𝑻𝑭 + 𝟒𝟔𝟎
𝟏𝑪° = 𝟏 𝑲 𝟏𝑭° = 𝟏𝑹° 𝟏𝑪° =
𝟗
𝟓
°𝑭
Thermal Equilibrium and Zeroth Law of Thermodynamics
Zeroth Law of Thermodynamics
“Two bodies are said to be in thermal equilibrium if they
have the same temperature.”
Thermal Expansion
Thermal Expansion of Solids
For linear expansion of solids, the
change in length (ΔL) of a solid,
say a rod, is:
1. proportional to the change in
temperature (ΔT). A rod
subjected to a temperature
increase of 40OC will expand
twice than when subjected to a
temperature increase of 20OC.
2. proportional to its original
length (ΔLo). When
subjected to the same
temperature change, long
rods will have greater
change in length than short
rods of the same material.
3. dependent on the material of which the
rod is made. An aluminium rod will
expand differently from a copper rod of
the same length even if subjected to the
same temperature increase.
∆𝑳 = 𝑳 − 𝑳𝟎 = 𝜶𝑳𝟎∆𝑻 = 𝜶𝑳𝟎(𝑻 − 𝑻𝟎)
where: α is the coefficient of linear
expansion of the material of which the
rod is made
Coefficient of linear expansion (α) – change in
length divided by the original length and change
in temperature
𝜶 =
∆𝑳
𝑳𝟎∆𝑻
=
𝑳 − 𝑳𝟎
𝑳𝟎(𝑻 − 𝑻𝟎)
Coefficient of area expansion (γ) – change in
area divided by the original area and change in
temperature
𝜸 =
∆𝑨
𝑨𝟎∆𝑻
=
𝑨 − 𝑨𝟎
𝑨𝟎(𝑻 − 𝑻𝟎)
𝜸 = 𝟐𝜶
Coefficient of volume expansion (β) –
change in volume divided by the
original volume and change in
temperature
𝜷 =
∆𝑽
𝑽𝟎∆𝑻
=
𝑽 − 𝑽𝟎
𝑽𝟎(𝑻 − 𝑻𝟎)
𝜷 = 𝟑𝜶
Calorimetry – science of
measuring the amount of heat
gained or lost in a chemical
reaction
Lt. calor – “heat”
Gk. Metron – “measure”
Joseph Black
– father of calorimetry
Molar Specific Heat of Gases
Gases have two kinds of specific heat: specific
heat at constant pressure and specific heat at
constant volume
𝑪𝑷 = 𝑪𝑽 + 𝑹
where: CP is the specific heat of an ideal gas at constant
pressure; CV is the specific heat of an ideal gas at
constant volume; R is the universal gas constant (R =
8.314 J/mol K or 8.314 J/mol CO)
Phase Change
Fusion or melting – change from solid to liquid
Melting point – temperature at which a solid
becomes a liquid
Solidification or freezing – change from liquid to solid
Freezing point – temperature at which a liquid
becomes solid
Latent Heat – heat needed to change the phase of an object
The heat added during a phase change is used to break the
forces between the molecules and not to increase the
kinetic energy (and hence the temperature) of the
molecules; phase change occur without a change in the
temperature of an object.
1. At portion AB, the
substance is in solid
phase. The heat being
added is used to raise
the temperature up to
TB. Temperature TB is the
melting point of the
substance.
2. At point B, the substance
starts to melt. The heat
supplied is used to melt the
solid. The temperature
remains constant until the
substance completely melts
(point C). Between points B
and C, the substance exists
in both solid and liquid
phases.
3. In portion CD, the
substance exists in
liquid phase. The heat
added is used to raise
the temperature up to
TD. Temperature TD is
the boiling point of the
substance.
4. The temperature remains
constant at TD as the
substance changes into
the gaseous phase. At
point E, the substance is
totally converted to gas.
Between points D and E,
the substance exists in
both liquid and gaseous
phases.
5. In portion EF,
the addition of
heat increases
the
temperature
of the gas.
6. Moving from right
to left starting from
point F represents
the cooling curve
of the substance.
Latent Heat – heat involved in phase change;
quantity of heat absorbed or released when a
substance changes its physical phase at
constant temperature (e.g. from solid to liquid at
melting point or from liquid to gas at boiling
point)
𝑸 = 𝒎𝑳
where: Q is the heat involved during the entire phase
change; m is the mass of the substance; L is the latent
heat
note: Q is positive if heat is absorbed and negative if heat
is released
1. Latent Heat of Fusion (Lf) – amount of heat
needed to change a unit mass of a substance
from solid to liquid phase at its melting point
𝑸𝒇 = 𝒎𝑳𝒇
2. Latent Heat of Vaporization (Lv) – amount of
heat needed to change a unit of mass of a
substance from liquid to gaseous phase at its
boiling point
𝑸𝒗 = 𝒎𝑳𝒗
3. Latent Heat of Sublimation (Ls) – heat
required to change a unit mass of a substance
from solid to gaseous phase at constant
temperature, without passing the liquid phase
𝑸𝒔 = 𝑸𝒇 + 𝑸𝒗
𝒎𝑳𝒔 = 𝒎𝑳𝒇 + 𝒎𝑳𝒗
How can we lessen the
impact of
climate change and
global warming?
How can we use
Earth’s heat as
energy source?
Lesson 13 - Temperature and Heat.pdf
Lesson 13 - Temperature and Heat.pdf

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Lesson 13 - Temperature and Heat.pdf

  • 1.
  • 2.
  • 3. Heat and Temperature Temperature – measure of the average kinetic energy of molecules making up an object Heat – energy in transit from one body to another because of the difference in temperature; it is the measure of the total kinetic energy of the particles of a body; SI Unit: joule (J) and calorie (cal)
  • 4. Heat Calorie – amount of heat needed to change the temperature of one gram of water from 14.5OC to 15.5OC at a pressure of 1 atm 1 calorie = 4.186 joules Mechanical equivalent of heat – the ratio 4.186 J/cal
  • 5. Temperature Scales Ice point – temperature at which ice melts under pressure of 1 atm Steam point – temperature at which water boils under a pressure of 1 atm
  • 6. Temperature Scales 1. Celsius and Fahrenheit Scales 𝑻𝑪 = 𝟓 𝟗 (𝑻𝑭 − 𝟑𝟐) 𝑻𝑭 = 𝟗 𝟓 𝑻𝑪 + 𝟑𝟐 2. Kelvin Scale 𝑻𝑲 = 𝑻𝑪 + 𝟐𝟕𝟑 3. Rankine Scale 𝑻𝑹 = 𝑻𝑭 + 𝟒𝟔𝟎
  • 7. 𝟏𝑪° = 𝟏 𝑲 𝟏𝑭° = 𝟏𝑹° 𝟏𝑪° = 𝟗 𝟓 °𝑭
  • 8.
  • 9.
  • 10. Thermal Equilibrium and Zeroth Law of Thermodynamics Zeroth Law of Thermodynamics “Two bodies are said to be in thermal equilibrium if they have the same temperature.”
  • 11.
  • 12. Thermal Expansion Thermal Expansion of Solids For linear expansion of solids, the change in length (ΔL) of a solid, say a rod, is: 1. proportional to the change in temperature (ΔT). A rod subjected to a temperature increase of 40OC will expand twice than when subjected to a temperature increase of 20OC.
  • 13. 2. proportional to its original length (ΔLo). When subjected to the same temperature change, long rods will have greater change in length than short rods of the same material.
  • 14. 3. dependent on the material of which the rod is made. An aluminium rod will expand differently from a copper rod of the same length even if subjected to the same temperature increase. ∆𝑳 = 𝑳 − 𝑳𝟎 = 𝜶𝑳𝟎∆𝑻 = 𝜶𝑳𝟎(𝑻 − 𝑻𝟎) where: α is the coefficient of linear expansion of the material of which the rod is made
  • 15. Coefficient of linear expansion (α) – change in length divided by the original length and change in temperature 𝜶 = ∆𝑳 𝑳𝟎∆𝑻 = 𝑳 − 𝑳𝟎 𝑳𝟎(𝑻 − 𝑻𝟎) Coefficient of area expansion (γ) – change in area divided by the original area and change in temperature 𝜸 = ∆𝑨 𝑨𝟎∆𝑻 = 𝑨 − 𝑨𝟎 𝑨𝟎(𝑻 − 𝑻𝟎) 𝜸 = 𝟐𝜶
  • 16.
  • 17. Coefficient of volume expansion (β) – change in volume divided by the original volume and change in temperature 𝜷 = ∆𝑽 𝑽𝟎∆𝑻 = 𝑽 − 𝑽𝟎 𝑽𝟎(𝑻 − 𝑻𝟎) 𝜷 = 𝟑𝜶
  • 18.
  • 19.
  • 20. Calorimetry – science of measuring the amount of heat gained or lost in a chemical reaction Lt. calor – “heat” Gk. Metron – “measure” Joseph Black – father of calorimetry
  • 21.
  • 22. Molar Specific Heat of Gases Gases have two kinds of specific heat: specific heat at constant pressure and specific heat at constant volume 𝑪𝑷 = 𝑪𝑽 + 𝑹 where: CP is the specific heat of an ideal gas at constant pressure; CV is the specific heat of an ideal gas at constant volume; R is the universal gas constant (R = 8.314 J/mol K or 8.314 J/mol CO)
  • 23. Phase Change Fusion or melting – change from solid to liquid Melting point – temperature at which a solid becomes a liquid Solidification or freezing – change from liquid to solid Freezing point – temperature at which a liquid becomes solid
  • 24. Latent Heat – heat needed to change the phase of an object The heat added during a phase change is used to break the forces between the molecules and not to increase the kinetic energy (and hence the temperature) of the molecules; phase change occur without a change in the temperature of an object.
  • 25. 1. At portion AB, the substance is in solid phase. The heat being added is used to raise the temperature up to TB. Temperature TB is the melting point of the substance.
  • 26. 2. At point B, the substance starts to melt. The heat supplied is used to melt the solid. The temperature remains constant until the substance completely melts (point C). Between points B and C, the substance exists in both solid and liquid phases.
  • 27. 3. In portion CD, the substance exists in liquid phase. The heat added is used to raise the temperature up to TD. Temperature TD is the boiling point of the substance.
  • 28. 4. The temperature remains constant at TD as the substance changes into the gaseous phase. At point E, the substance is totally converted to gas. Between points D and E, the substance exists in both liquid and gaseous phases.
  • 29. 5. In portion EF, the addition of heat increases the temperature of the gas.
  • 30. 6. Moving from right to left starting from point F represents the cooling curve of the substance.
  • 31. Latent Heat – heat involved in phase change; quantity of heat absorbed or released when a substance changes its physical phase at constant temperature (e.g. from solid to liquid at melting point or from liquid to gas at boiling point) 𝑸 = 𝒎𝑳 where: Q is the heat involved during the entire phase change; m is the mass of the substance; L is the latent heat note: Q is positive if heat is absorbed and negative if heat is released
  • 32. 1. Latent Heat of Fusion (Lf) – amount of heat needed to change a unit mass of a substance from solid to liquid phase at its melting point 𝑸𝒇 = 𝒎𝑳𝒇 2. Latent Heat of Vaporization (Lv) – amount of heat needed to change a unit of mass of a substance from liquid to gaseous phase at its boiling point 𝑸𝒗 = 𝒎𝑳𝒗
  • 33.
  • 34. 3. Latent Heat of Sublimation (Ls) – heat required to change a unit mass of a substance from solid to gaseous phase at constant temperature, without passing the liquid phase 𝑸𝒔 = 𝑸𝒇 + 𝑸𝒗 𝒎𝑳𝒔 = 𝒎𝑳𝒇 + 𝒎𝑳𝒗
  • 35. How can we lessen the impact of climate change and global warming?
  • 36. How can we use Earth’s heat as energy source?