# Peter Lux

## Why do metals have low specific heat capacities? – they don’t

I came across the following answer to the question “Why do metals have low specific heat capacities?”:

Metal atoms in pure metal are very close together and are able to transfer heat easily via conduction from one atom exciting the other atoms next to it. So the amount of energy it takes to heat a metal is relatively small to that of water for example.

Non-metals have crystal structures generally farther apart and thus don’t transfer energy as efficiently.1

Most of the other answers are in similar vein as are the answers to the same question in WikiAnswers2.

The only problem is that the answers are totally wrong. My experience of such websites is that there is no point posting the correct answer since people prefer the simpler wrong answer.

The fact is that the specific heat capacities of metals differ little from non-metals of similar atomic mass. The relationship between specific heat capacities and atomic mass is given by the Dulong Petit Law3.

## What Is Specific Heat

It is the amount of energy needed to heat up a certain amount of a substance (usually a gram) by one degree. Its units are J/(g K).

For an atom in a simple crystal lattice the energy goes into making the atom vibrate more. The more atoms there are in a given mass of substance the more energy it can absorb before raising the temperature by one degree. If we look at the heat capacity for the same number of atoms – the molar heat capacity (J/(mol K) then it is roughly constant (the Dulong Petit law):

 Aluminium 24.20 J/(mol K) Phosphorous 21.19 J/(mol K) Sulphur 23.23 J/(mol K) Iron 25.10 J/(mol K) Arsenic 24.64 J/(mol K)

The heavier elements contain fewer atoms to absorb the energy per gram of material and therefore tend to have lower specific heat capacities.

Another factor is that a thin metal tray coming out of the oven is going to cool quicker than a thicker, heavier glass dish. While you can pick a metal tray up a few minutes of it coming out of the oven I suggest you do not try to do the same thing with a heavy metal frying pan.

So do not believe everything you read on the internet – particularly where people who do not know the answer to a question vote on what the best answer is.  Wikipedia tends to be much better since the contributions are discussed and edited although can still contain glaring errors.

1  Why do metals have low specific heat capacities, Yahoo Answers (https://uk.answers.yahoo.com/question/index?qid=20080917234005AA2jj94)

3 Dulong-Petit Law, Wikipedia (http://en.wikipedia.org/wiki/Dulong%E2%80%93Petit_law)