Talk:Specific heat capacity

Please wait

Please wait until I am done to say whether I have improved or ruined the article. Thank you. --Jorge Stolfi (talk) 03:25, 11 May 2019 (UTC)

Removed section

I have removed the following section:

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Thermodynamic relations and definition of heat capacity {{anchor|Heat capacity}}

The change in temperature of a substance when a given quantity of heat is absorbed or rejected by it is called as heat capacity {taken from N.C.E.R.T.}. Written mathematically we have

$\Delta e_{\text{system}}=e_{\text{in}}-e_{\text{out}},$

or

$\mathrm {d} U=\delta Q-\delta W.$

For work as a result of an increase of the system volume we may write

$\mathrm {d} U=\delta Q-P\,\mathrm {d} V.$

If the heat is added at constant volume, then the second term of this relation vanishes, and one readily obtains

$\left({\frac {\partial U}{\partial T}}\right)_{V}=\left({\frac {\partial Q}{\partial T}}\right)_{V}=C_{V}.$

This defines the heat capacity at constant volume, $C$_V, which is also related to changes in internal energy. Another useful quantity is the heat capacity at constant pressure, $C$_P. This quantity refers to the change in the enthalpy of the system, which is given by

$H=U+PV.$

A small change in the enthalpy can be expressed as

$\mathrm {d} H=\mathrm {d} U+\,\mathrm {d} (PV),$

$\mathrm {d} H=\delta Q-\delta W+\,\mathrm {d} (PV),$

$\mathrm {d} H=\delta Q-P\mathrm {d} V+\,P\mathrm {d} V+\,V\mathrm {d} P,$

$\mathrm {d} H=\delta Q+V\,\mathrm {d} P,$

and therefore, at constant pressure, we have

$\left({\frac {\partial H}{\partial T}}\right)_{P}=\left({\frac {\partial Q}{\partial T}}\right)_{P}=C_{P}.$

These two equations:

$\left({\frac {\partial U}{\partial T}}\right)_{V}=\left({\frac {\partial Q}{\partial T}}\right)_{V}=C_{V},$

$\left({\frac {\partial H}{\partial T}}\right)_{P}=\left({\frac {\partial Q}{\partial T}}\right)_{P}=C_{P}$

are property relations and are therefore independent of the type of process. In other words, they are valid for any substance going through any process. Both the internal energy and enthalpy of a substance can change with the transfer of energy in many forms i.e., heat.<ref>''Thermodynamics: An Engineering Approach'' by Yunus A. Cengal and Michael A. Boles.</ref>

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This text has a number of problems that I do not see how to fix:

• It gives derivations in textbook style. Wikipedia is not a texbook.
• It does not define or explain many symbols, such as U, H, δ etc.
• I cannot tell what is the goal, nor what it adds to the simple definitions of $c_{\mathrm {V} }$ and $c_{\mathrm {P} }$.

--Jorge Stolfi (talk) 05:52, 11 May 2019 (UTC)