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This question is about degrees of freedom.

It is given that the rotational degrees of freedom of $H_2$ only start appearing at T>100 K, whereas the vibrational degrees of freedom start appearing for T>1000 K.

How much heat does it take to raise the temperature of one mole of $H_2$ from 70 K to 200 K in an isobaric process?

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For solving this question, we are going to use Q=nCpdT , here Cp is the specific heat at const pressure.

But since at 100K the degrees of freedom change, you need to breakdown the equation of heat in two parts, the first where deg of freedom is 3( only translational motion) and second where deg of freedom is 5 when temperature is 100 K.

Now formula for Cp is fR/2 + R, so just substitute f=3 for temp between 70 and 100 and f = 5 for temp between 100 and 200. Add the two equations and you will get the answer.

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