Answer to Question #73265 in Physical Chemistry for Barbara

Question #73265

Paraffin wax has a melting point of 60oC, and carnuaba wax has a melting (range, really, but, in general) point of 80oC.

If I heat paraffin wax to 80oC, and pour a thin layer directly on skin, there is no burn. If I pour a thin layer of 80oC carnauba wax directly on skin, the skin is likely to acquire a 1st or even 2nd degree burn.

What thermal property of these waxes is the most likely culprit for this difference?

Paraffin wax is made up entirely of alkanes of various lengths (average is C25); carnauba wax is mix of alkanes with a high percentage of fatty acids and fatty alcohols, and some esters (specific percentages varies).

Expert's answer

There are two main factors causing burn: wax temperature and its heat capacity. Liquid carnauba wax has a higher temperature because of a higher melting point and a greater heat capacity because of the content of fatty acids and fatty alcohols. Therefore, each gram of carnauba heats the skin to a higher temperature and acts for a long time causing the burn.