Homework Help: chemistry

Posted by Anmol on Thursday, November 5, 2009 at 5:37pm.

Hii i was wondering if u cud help me solve this problem..im not sure how to start it.
Calculate the delta H for the reaction of solid potassium with liquid water. If a 5.00 g piece of potassium is added to 1.00 kg of water at 24 degrees celsius what is the final temperature of the water after the reaction occurs? Assume that all the heat is used to raise the temperature of the water. Assuming 100% yeild, what is the concentration of KOH after the reaction is complete? What volume of Hydrogen was produced?

chemistry - Anmol, Thursday, November 5, 2009 at 5:38pm
Also this is assumed that it occurs at 1 atm. and the final temperature of the water is the same temperature of the gas.
chemistry - DrBob222, Thursday, November 5, 2009 at 5:41pm
You start by writing the equation and balancing it.
2K + 2H2O ==> 2KOH + H2

Then you pray over it. I think you must have either delta H or the final T. Check my thinking.
chemistry - Anmol, Thursday, November 5, 2009 at 6:47pm
no neither of them are given..just the assumptions i mentioned
chemistry - DrBob222, Thursday, November 5, 2009 at 8:01pm
Use the equation above for the balanced equation. Convert 5.00 g K metal to moles. moles = grams/molar mass.

Then use the coefficients in the balanced equation to convert moles K metal to moles KOH and in a separate calculation determine the moles H2 gas.

(KOH) = moles/kg solvent = molality.
Volume of H2 gas at STP = (22.4 L/mol) x moles H2 from above. Then convert from STP to 24 degrees celsius.

Finally, you can't calculate delta H without the final T and you can't calculate final T without delta H.

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