Twenty flashcards covering heat, temperature and the laws of thermodynamics. Includes specific and latent heat calculations, the three modes of heat transfer, the Stefan-Boltzmann law, the ideal gas law and its component gas laws, kinetic theory, entropy, ther...
Twenty flashcards covering heat, temperature and the laws of thermodynamics. Includes specific and latent heat calculations, the three modes of heat transfer, the Stefan-Boltzmann law, the ideal gas law and its component gas laws, kinetic theory, entropy, thermodynamic processes, heat engines and Carnot efficiency. Formula-led revision for A-Level and AP Physics 2.
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Temperature is a measure of the average kinetic energy of particles. Heat is the energy transferred between bodies because of a temperature difference.
The temperature at which particle kinetic energy is minimal: 0 K = β273.15 Β°C. Convert with
π
(
K
)
=
π
(
β
C
)
+
273.15
T(K)=ΞΈ(
β
C)+273.15.
Q=mcΞT β energy transferred equals mass Γ specific heat capacity Γ temperature change. Units of
π
c: J kgβ»ΒΉ Kβ»ΒΉ.
Q=mL β energy transferred during a change of state at constant temperature, where
πΏ
L is the specific latent heat of fusion or vaporisation.
The supplied energy breaks intermolecular bonds, increasing potential energy rather than kinetic energy, so the temperature does not rise.
Conduction (particle collisions and free electrons in solids), convection (bulk fluid movement from density differences) and radiation (emission of electromagnetic waves).
π
=
π
π
π΄
π
4
P=eΟAT
4
β radiated power depends on emissivity, surface area and the fourth power of absolute temperature.
π
π
=
π
π
π
PV=nRT (molar form) and
π
π
=
π
π
π΅
π
PV=Nk
B
β
T (molecular form), where
π
=
8.31
R=8.31 J molβ»ΒΉ Kβ»ΒΉ and
π
π΅
=
1.38
Γ
10
β
23
k
B
β
=1.38Γ10
β23
J Kβ»ΒΉ.
Boyle:
π
β
1
/
π
Pβ1/V at constant
π
T. Charles:
π
β
π
VβT at constant
π
P. Gay-Lussac:
π
β
π
PβT at constant
π
V.
πΈ
π
βΎ
=
3
2
π
π΅
π
E
k
β
β
=
2
3
β
k
B
β
T β the mean translational kinetic energy of a gas molecule depends only on absolute temperature.
Molecules are point masses in random motion, collisions are perfectly elastic, intermolecular forces are negligible except during collisions, and collision time is negligible.
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other β this is what makes temperature measurable.
Ξ
π
=
π
β
π
ΞU=QβW β the change in internal energy equals heat added to the system minus work done by the system. It expresses conservation of energy.
Isothermal: constant
π
T (
Ξ
π
=
0
ΞU=0). Adiabatic: no heat exchange (
π
=
0
Q=0). Isobaric: constant
π
P. Isochoric: constant
π
V (
π
=
0
W=0).
The total entropy of an isolated system never decreases; heat flows spontaneously from hot to cold, and no process can convert heat entirely into work.
A measure of the number of microscopic arrangements available to a system β effectively its disorder or the unavailability of its energy for doing work.
The entropy of a perfect crystal approaches zero as temperature approaches absolute zero, and absolute zero cannot be reached in a finite number of steps.
π
max
β‘
=
1
β
π
πΆ
π
π»
Ξ·
max
β
=1β
T
H
β
T
C
β
β
, using absolute temperatures of the cold and hot reservoirs. No real engine can exceed this.
W=PΞV. On a pressure-volume diagram, work done equals the area under the curve.
U=
2
3
β
nRT β it depends only on temperature and the amount of gas, not on pressure or volume.
