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Topic: Enthalpy  (Read 1666 times)

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Offline theogthomas

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Enthalpy
« on: December 22, 2017, 08:38:12 PM »
How does the number of hydroxyl groups in the solute molecule affect the temperature of dissolution when dissolving alcohols in water inside of a calorimeter?

I know that if the number of OH (hydroxyl) groups along the carbon chain in alcohol increases, more solute-water hydrogen bonding is possible, and solubility generally increases, and the opposite happens when you increase the carbon chain (because less solute-water hydrogen bonding is possible) , but how does this affect temperature of dissolution in a calorimeter?

any help appreciated! thank you in advance.
« Last Edit: December 22, 2017, 09:33:03 PM by theogthomas »

Offline theogthomas

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Re: Enthalpy
« Reply #1 on: December 22, 2017, 08:42:50 PM »
Does an increase in solubility mean an increase in temperature in the calorimeter because more bonds are being broken (through dissolution)?
« Last Edit: December 22, 2017, 09:28:47 PM by theogthomas »

Offline Enthalpy

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Re: Enthalpy
« Reply #2 on: December 23, 2017, 04:55:33 PM »
Hi theogthomas!

Whether the dissolution of an alcohol shall absorb or release heat isn't simple. The dissolution must break alcohol-to-alcohol bonds and water-to-water bonds to create water-to-alcohol bonds (all intermolecular ones), so it's a matter of relative strength. And it may also depend on if all the possible bonds are realised in the solid polyol, which some molecule shapes supposedly prevent.

Polyols like glycerol, sorbitol, xylitol... absorb heat when they dissolve in water, but I wouldn't dare to draw a general rule from that.

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