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CBSE Class 11-science Answered

What is meant by the term ' Molar specific heat ' of a gas?  The molar specific heat of hydrogen in the temperature range of about 250 K to 750 K is about (5/2) R.  At lower temperatures the value of molar specific heat of hydrogen decreases to the value typical of monoatomic gases (3/2) R while at higher temperatures, it tends to the value (7/2) R.  Explain.
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
answered-by-expert Expert Answer

Molar specific heat capacity of a gas refers to the amount of energy required for 1 mole of a substance to raise its temperature by 1 K.  In the temperature beyond 70 kelvin, rotational motion of H2 gas starts.  So at 250 K < T < 750, the number of degrees of freedom becomes five -2 rotational and 3 translational

Therefore,  Cv =f/2 R becomes, Cv = 5/2 R.  For lower temperatures only translational degrees of freedom will exist and no rotational freedom.

Therefore,  Cv = 3/2 R.

Answered by | 04 Jun, 2014, 03:23: PM

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