We were discussing various forms of work
in thermodynamics such as displacement work or PdV work, paddle wheel work, flow work and shaft work in thermodynamics in our
previous posts.
Today we will see here the basic difference between
specific heat and latent heat. First let us see here the detailed explanation
of specific heat of a substance and after that we will see here latent heat
with the help of this post.
Specific heat
Specific
heat of a substance is basically defined as the quantity of heat which is
required to raise the temperature of the unit mass of substance by unit degree.
Specific heat of a substance will be indicated by c and we must note it here that
word c will be written in small letter for indicating the specific heat.
Let
mass of substance (m) is 1 kg i.e. unit mass of substance and increase in
temperature (∆T) is one degree Kelvin. Therefore c = Q or we may say that heat
required to increase the temperature of one kg of substance by one degree
Kelvin will be termed as specific heat of the substance.
Product
of mass of substance and specific heat of substance will be termed as heat
capacity and heat capacity of substance will be indicated by capital letter C.
Heat
capacity of substance C = m. c
Heat
capacity of substance C = Q / ∆T
Let us see here the unit of specific heat
Unit
of specific heat will be J/Kg. K and it could be easily determined by the above
formula, while heat capacity will be measured in J/ K.
Types of specific heat
There are basically two types of
specific heat i.e. specific heat at constant volume and specific heat at
constant pressure
Let us see here first specific heat at constant volume (cv)
Specific heat at constant volume of a
substance is basically defined as the quantity of heat which is required at
constant volume to raise the temperature of the unit mass of substance by unit
degree. Specific heat at constant volume of a substance will be indicated by c v.
Specific heat at constant pressure (cp)
Specific heat at constant pressure of a
substance is basically defined as the quantity of heat which is required at
constant pressure to raise the temperature of the unit mass of substance by
unit degree. Specific heat at constant pressure of a substance will be
indicated by c p.
Latent heat (L)
Latent heat is basically defined as the amount of
heat energy required for changing the phase of a unit mass of a substance at a
given pressure and temperature. Latent heat is shown by L and it unit is J/Kg
in S.I unit system.
Types of Latent heat
As we know that there are basically three phases of
substance or matter and substance or matter can exist in these three phases
i.e. solid, liquid and gas or vapour. Hence, there will be basically three
types of latent heat as mentioned here.
Latent heat of fusion (Lf)
Latent heat of fusion is basically defined as the
amount of heat energy which is required to melt the unit mass of solid in to
liquid or to freeze the unit mass of liquid to solid at given temperature and
pressure.
Latent heat of vaporization (LV)
Latent heat of vaporization is basically defined as
the amount of heat energy which is required to vaporize the unit mass of liquid
in to vapour or to condense the unit mass of vapour to liquid at given
temperature and pressure.
Latent heat of sublimation (Ls)
Latent heat of sublimation is basically defined as
the amount of heat energy which is required to convert the unit mass of solid
in to vapour or amount of heat energy which is required to convert the unit mass
of vapour to solid at given temperature and pressure.
We must note it here that latent heat of fusion will
not be much affected due to pressure but latent heat of vaporization will be
quite sensitive to pressure.
Reference:
Engineering thermodynamics, By P. K. Nag
Engineering thermodynamics, By S. K. Som
We will see another important topic i.e. Stirling cycle and Ericsson cycle in the category of thermal engineering
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