I always learned that water has the highest specific heat, but I recently saw that hydrogen has a specific heat as high as $\pu{14 cal g^-1 °C^-1}$ and helium has a specific heat of $\pu{5 cal g^-1 °C^-1},$ which would be much higher than water? Is this true? and how can it be if there are so many “proofs” in nature, showing that water has the highest specific heat?
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$\begingroup$ related: chemistry.stackexchange.com/q/26651/23561 $\endgroup$– A.K.Oct 30, 2018 at 1:13
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1$\begingroup$ Yes, that's true, except that the figures are in Joules, not calories. Still, they are a good deal bigger than that for water. There is nothing strange or anomalous about it. $\endgroup$– Ivan NeretinOct 30, 2018 at 6:01
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$\begingroup$ You would be better to compare heat capacity in joules/mole/K rather than mass, in that case hydrogen is approx 28 , water approx 75, but for example benzene 117 and anthracene 211. $\endgroup$– porphyrinOct 30, 2018 at 10:00
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2$\begingroup$ I bet the interior of the sun has a very high specific heat. $\endgroup$– Curt F.Jun 23, 2021 at 0:17
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2 Answers
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Since we are really interested in the heat effects of a liquid at somewhat normal temperatures. I am going to disregard the extremes displayed by diatomic gaseous elements and look at liquids at stp. For years water was considered the champion, but I reasoned that the more massive heavy water would show an even greater resistance to the transfer of heat motion. Not only is duterium based water higher but it appears that tritium based water is even higher.
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$\begingroup$ +1 But giving the values would make the answer better. $\endgroup$ Jun 23, 2021 at 9:27
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$\begingroup$ What do you mean by “resistance to transfer of heat motion”? An explanation of why the heavier waters have higher specific heat would make this a much better answer. (Hint: think about vibrational frequencies) $\endgroup$– AndrewJun 23, 2021 at 12:30
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This may not be the absolute highest, but on a mass basis hydrogen gas has more than three times the specific heat as water under normal laboratory conditions. Diatomic gases under ambient conditions generally have a molar specific heat of about $\pu{7 cal mol^-1 K^-1},$ and one mole of hydrogen has only $\pu{2 g}$ mass. Thus $\pu{3.5 cal g^-1 K^-1}$ for hydrogen versus $\pu{1 cal g^-1 K^-1}$ for water.
Helium, contrary to the question, is $\pu{5 cal mol^-1 K^-1},$ not $\pu{7 cal g^-1 K^-1}.$
answered Oct 30, 2018 at 11:04