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definition of specific heat capacity
quantity of thermal energy Q per unit mass m required to raise the temperature of a substance by one degree
formula for specific heat capacity c
c = Q/mΔθ
J kg¯ ¹ K¯ ¹
definition of specific latent heat
the quantity of thermal energy required per unit mass to change the state of a substance without any change in temperature
specific latent heat of fusion Lf
solid to liquid
Lf = Q/m
J kg¯ ¹
specific latent heat of vaporisation Lv
liquid to vapour
Lv = Q/m
J kg¯ ¹
internal energy definition
the sum of random distribution of kinetic energy and potential energy associated with the molecules of a system
unit for internal energy
J - joules
in U, what is potential energy due to
Ep is due to the intermolecular forces, which depend on the separation of molecules.
as separation increases (ie more disordered), Ep increases
what does U of an ideal gas depends on
kinetic energy only (and therefore is only affected by temperature)
this is because for ideal gases, the Ep of the molecules is zero since there is no intermolecular forces
U of the system depends only on its state (like temperature, pressure). If it goes to the same state, ΔU=0
what is the first law of thermodynamics
the increase in the internal energy ΔU of the system is the sum of the heat supplied Q to the system and work done W on the system
first law of thermodynamics formula
ΔU = Q + W
if heat is supplied to the system
Q is positive
if heat is taken from the system
Q is negative
compression ie work done ON gas
W is positive
expansion ie work done BY gas
W is negative
how to calculate work done of a system
area under pressure-volume graph
W = pΔV
Note
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