Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: zakid on February 17, 2009, 02:59:47 PM

Title: Enthalpy changes.
Post by: zakid on February 17, 2009, 02:59:47 PM

I want to find out if my reasoning is correct...

I want to calculate the enthalpy change of this reaction
NaHCO3 + HCl -> NaCl + CO2 + H2O

...using Hess's Law...

1)  2NaHCO3 -> Na2CO3 + CO2 + H2O

2)  Na2CO3 + 2HCl -> 2NaCl + CO2 + H2O

1) 7g of hydrogencarbonate
50cm^3 of hydrochloric acid
deltaT=5K

2) 4g of hydrogencarbonate
50cm^3 of hydrochloric acid
deltaT=9,5K

2H1=H2+H3

H2= 0,057 x 4,18 x 5 = -1,19kJ

H3=0,054 x 4,18 x 9,5 = 2,14kJ

H1=(-1,19kJ - 2,14kJ):2= -1,665kJ

Is this correct?

Title: Re: Enthalpy changes.
Post by: Astrokel on February 17, 2009, 08:50:50 PM

Quote

2H1=H2+H3

Which is which?

Title: Re: Enthalpy changes.
Post by: Donaldson Tan on February 18, 2009, 07:03:37 AM

You might need to some labelling of your terms. Also use the sub and sup tags. It would help a lot in interpreting your text.

Title: Re: Enthalpy changes.
Post by: zakid on February 18, 2009, 01:31:21 PM

Nevermind, I've already figured it out. I'll try using better notation next time.