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April 1, 2015

Homework Help: ap chemistry!! help!!

Posted by john on Tuesday, January 9, 2007 at 3:44pm.

some solutes have large heats of solution, and care should be taken in preparing solutions of these substances. The heat evolved when sodium hydroxide dissolves is 44.5 KJ/mol. What is the final temperature of the water, originally at 20.0 degrees Celcius. used to prepare 500.0 cm cubed of 6.00M NaOH solution? Assume all the hat is absorbed by 500cm cubed of water, specific heat =4.18 J/g Degrees Celcius!!!!

1 mol NaOH in 1L solution = 1M
6 mols NaOH in 1 L solution = 6.00 M
3 mols NaOH in 1/2 L (500 cc) soln = 6.00 M,

q = 3 mols x 44.5 kJ/mol = 133.5 kJ.

The quantity of q is in kJ but specific heat of water is in J/g so we need to change kJ to J.
133.5 kJ x 1000 J/kJ = 133,500 J.

Then
q = massH2O x specific heat x (Tf - Ti)=
where Tf is final T and Ti is initial T.
133,500=500 x 4.18 x (Tf - 20)=
Solve for Tf.

Note the correct spelling of Celsius.
Post your work if you get stuck and need further assistance.

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