[Stickslikeglue]

Right ive looked around a bit but i havent found anything that really answers my question yet
 
i have the equation:

2NaHCO₃ ==> Na₂CO₃ + H₂0 + CO₂

i reacted NaHCO₃ with HCL and did the same with Na₂CO₃

getting the equations:

NaHCO₃ + HCl ==> NaCl + CO₂ + H₂0 with delta H of approx.-34kj/mol

and

Na₂CO₃ + 2HCL ==> 2NaCl + CO₂ + H₂O with delta H of approx. 25kJ/mol

can i draw an enegry cycle fomt his data alone to calculate the enthalpy for the decomposition of NaHCO₃ and if so how can i do it?

thanks in advance! Bill

[Astrokel]

Yes, it's actually a simple energy cycle. Can you try it out yourself first?

kelvin

[Stickslikeglue]

i have done! but not here

erm best way to show it...

2NaHCO₃ ==>Na₂CO₃ + H₂0 +CO₂
     |                                               |
     |   -34kJ                                     |  +25kJ
     v                                               V

                        NaCl + CO₂ +H₂O   (#)


i then get delta H over all to equal 2x(-34) - (+25) to get -95kJ/mol

The bit that confuses me is the  equation labeled with the hash. the reaction with NaHCO₃ and HCl or with Na₂CO₃ does not give this equation. 2NaHCO₃ has two lots of everything and Na₂CO₃ has two lots of NaCl! Or is that ok because you already have one lots of water and carbon dioxide on the right hand sde of the equation already?

Hmm think ive made with as clear as mud :S hope you understand where im confused.
Thanks Again! Bill

[Astrokel]

      2NaHCO3 ---> Na2CO3 + H20 +CO2
         |                  |
         | +2HCl         | +2HCl
         |                 |
         V                 V
      2NaCl + 2CO2 + 2H20
       

Yes, the equation with hash is wrong! You multiply by 2 with the (-34), then you should have also multiply
(NaCl + CO2 + H20) by 2 to 2NaCl + 2CO2 + 2H2O, otherwise it is not balanced.

When u do an energy cycle,

1) Ensure that the reagents you 'add' to the cycle such as in this case, HCl, is balanced. What is mean by balance is the amount of HCl 'added' in the clockwise direction is the same as the anticlockwise.

2) Ensure the final products of the clockwise and anticlockwise direction are the same, in this case, its the one highlighted in blue.


I think you are asking about this?

Kelvin

                               

[Stickslikeglue]

Ahhh yes thanks alot just about makle sense now!