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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: KYR_Singularity on February 11, 2014, 03:13:53 PM

Title: Calculating enthalpy change for two solution mixture
Post by: KYR_Singularity on February 11, 2014, 03:13:53 PM
25.0 cm3 of 2.00 mol dm-3 HCl(aq) was mixed with 25.0 cm3 of 2.00 mol dm-3 NaOH(aq). The temperature increased from 22.5°C to 34.5°C. Find the enthalpy change of reaction for the following equation:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l).
 
how do you work out the energy change in this reaction ?
please show all the work out  , thank you
Title: Re: Calculating enthalpy change for two solution mixture
Post by: zsinger on February 11, 2014, 06:15:26 PM
See:  Hess's Law.  Theres your hint….now lets see some work :)
        Zack
Title: Re: Calculating enthalpy change for two solution mixture
Post by: KYR_Singularity on February 12, 2014, 05:22:10 PM
HCL + NaOH -> NaCl + H2O
(25+25) x 4.18 x 12 = 2508 J
25 Volume reacted
25 x2 / 1000 = 0.05 mol
2508/0.05=50.16KJ/mol
^H = -50.16KJ/mol
is this right ? thanks for the tip anyway  :D
Title: Re: Calculating enthalpy change for two solution mixture
Post by: Borek on February 12, 2014, 05:41:18 PM
Doesn't look bad, although you may want to take water produced to the total mass.

Some will consider it nitpicking, but it is almost a 2% difference.
Title: Re: Calculating enthalpy change for two solution mixture
Post by: zsinger on February 12, 2014, 07:23:38 PM
Borek is correct.  Otherwise, you got it!
           -Zack
Title: Re: Calculating enthalpy change for two solution mixture
Post by: Benzene on February 12, 2014, 08:18:19 PM
In Hess's Law, it states that the sum δH products-δH reactants = δH reaction
Is the δH of the products and reactants calculated from the δH of formation? or combustion?
Title: Re: Calculating enthalpy change for two solution mixture
Post by: zsinger on February 12, 2014, 09:23:09 PM
(heats of formation of products) and subtract (heats of formation from reactants).  Thank you Mr. Hess…..may I have another?   :).  Heats of formation.
        -Z