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On eating powdered glucose I felt a cold sensation in my mouth. Then I thought it would be a result of the reaction between saliva and glucose. Then I thought that this would imply that the reaction would be endothermic. I don't find myself to be pretty sure and need to know whether I am right or not. Why would the reaction be endothermic in spite of the fact that glucose is readily soluble in saliva?

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  • $\begingroup$ Was this chemically pure glucose? $\endgroup$ – Lighthart Aug 24 '16 at 20:08
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    $\begingroup$ Why do you think dissolving something that is readily soluble can't be endothermic? $\endgroup$ – Michael DM Dryden Aug 25 '16 at 2:09
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    $\begingroup$ Dissolution can certainly be endothermic. Whether a reaction happens is controlled by $\Delta G$ not $\Delta H$ $\endgroup$ – orthocresol Aug 25 '16 at 5:06
  • $\begingroup$ It was glucose-d and 99.4% pure.Do molecules use my mouth's heat tobreak their bonds and get salivated and as a result the cold sensation? $\endgroup$ – Pewpaled Aug 25 '16 at 13:02
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The dissolution of glucose in an aqueous solution is an endothermic process. As stated in a comment, a reaction need not be exothermic to be spontaneous. Don't forget about the entropy term.

Simply put, the glucose dissolved endothermically in your saliva causing a heat transfer from your mouth to the glucose/saliva solution, resulting in a slight decrease in the temperature of your mouth, making it cooler than it was prior do dissolving the glucose.

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