Every day we use chemical reactions to perform mechanical work by creating either heat (e.g. in a piston engine) or electricity (batteries). I know muscles perform work by taking stored chemical energy and converting it directly into mechanical force.

Other than in organic chemistry, are there any examples of chemical reactions that we use to perform mechanical work without the intermediate step of harnessing the heat or electrical potential created by the reaction?

  • $\begingroup$ Well, it's really the rapid evolution of gas (e.g., from combustion) that will perform the expansion work in a piston, not the heat per se. Would you discount other (non-combustion) reactions that produce gases to perform $PV$ work? $\endgroup$
    – Greg E.
    Jul 18 '14 at 20:17
  • $\begingroup$ The heat is doing at least some of the work by expanding non-reactant and production gases. I always thought it was the major portion, but I might be wrong. I guess what I'm looking for is an example where the reactions are not significantly exothermic. Reactions that produce gases would not be discounted. $\endgroup$
    – NateT
    Jul 18 '14 at 20:51
  • $\begingroup$ Sorry, I may have been unclear in my phrasing. I just meant to emphasize that it's the gas itself that performs the work while expanding, though of course the amount of expansion is partially temperature-dependent. $\endgroup$
    – Greg E.
    Jul 18 '14 at 21:12
  • $\begingroup$ Physical reactions- phase transformations can do work from heat- do you count that as a chemical reaction? $\endgroup$ Oct 1 '14 at 11:24
  • $\begingroup$ No, I suppose not. And it's the exact opposite of what I'm trying to ask about. I've researched Greg E.'s comment and, yes, the majority of work in a piston engine is performed by evolution of gas. However, the very same reaction is highly exothermic, and so the accompanying heat must be dealt with. I'm looking for a an example of a chemical reaction that can perform mechanical work without generating (much) heat. A battery is one example, but its resultant energy form is electrical, not mechanical, so an extra step is needed. $\endgroup$
    – NateT
    Oct 2 '14 at 4:36

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