If I've this two following solutions:

 

A - 0,5g of KIO₃ in 250 mL of H₂O;

 

B - 1g of starch dissolved in 250 mL of boiling H₂O. Add 0,2g of NaHSO₃ and 5 mL of sulfuric acid 6M solution. Dilute in 500 mL of water.

 

And if I mix it, will the reaction be endothermic or exothermic?

 

Thanks.

 

(excuse I post this topic in organics. I do not perceived it)

Edited July 18, 201015 yr by Henry

Right an equation for the reaction showing the reactants and the products. Then use a book of data to look up the bond strengths in the reactant and products and add them up. Once youve got that you will be able to find the difference in enthalpy and therefor whether the reaction is exo or endothermic

Okay, so you got a solution of diluted potassium iodate. Another solution of starch (corn, wheat?) being liquified by sulfuric acid, breaking the glycosidic linkage into smaller oligosacharides. The sodium thiosulfate is there as an antioxidant for the iodate, I'm guessing?

 

Since its sorta a complex reaction, with starch this may not be easy to simply pull out the book at write down the bond energy like Horza mentioned. I'm not too familiar with "flour bleaching" methods, but I'm guessing it would be exothermic... probably very little energy given off, part B should give off a good amount of heat energy breaking down all the bonds with acid, but combined I'm guessing it's more of a replacement reaction attacking the hydroxy groups with Iodine. That's my 2-cents, maybe someone smarter than I will respond ;P

In true, the occurred reaction are the following:

First stage: IO₃⁺ + 3HSO₃^- --> I^- + 3H⁺ + 3SO₄^2-

Second stage: I^- + IO₃⁺ + H⁺ --> I₂ + H₂O

Third stage: I₂ + corn starch --> blue compound

Fourth stage: I₂ + HSO₃^- + H₂O --> 2I^- + SO₄^2- + 3H⁺

so, my trouble is to know what is the enthalpy of first-fourth stage system. The yours explanations was useful, thanks. But, For this total system, the enthalpy will go to increase or to decrease, considering the four stages as a whole?