Solving Thermodynamics Problem with Hydrochloric Acid and Sodium Bicarbonate

[KingNothing]

Alright, so we did three labs, and for some reason I just cannot get lab B. It's so dang frustrating, too. What we did was mix 50 mL of 1.00 molar hydrochloric acid with 2.00 grams of sodium bicarbonate.

We made our own calorimeter, they are styrofoam cups, and their specific heat is 16.7. Anyway, our 'heat evolved' (final heat) was 18.7 degrees, and the HCl started at 21.5 degrees. I think I calculated the lab heat alright:

specific heat of water/HCL * mass of hcl (grams) * change in temp + 16.7(some heat of the cup) * change in temp

4.18 * 0.05 * -2,8 + 16.7 * -2.8
To get -47.3452...

Please tell me if there is an error there.

Anyhoo...now to get the theoretical heat, I am just...i dunno...missing something huge. Black means solid, red means liquid, green means gas, blue means aqueos.

HCl + NaHC0_3 -> NaCl + CO_2 + H_2O

Then (and I think I might be doing something wrng here too) I split them up so I can look at their heats of formation:

H + Cl + Na + HCO_3 -> Na + Cl + C0_2 + H_2O
Now, I figured since both chlorines are aqueous, they cancel out, and hydrogen, CO_2 and H_2O all have 0 heat of formation.

So I figured HC0_3 is -691.1 (from a table), Na is -239.7 (from a table), and my theoretical heat is 451.4 KJ/mol.

Where did I go wrong?

 

[KingNothing]

Can anyone help me with this? I need it for tomorrow!

 

[wais]

It looks like you have made a few errors in your calculations. First, in your calculation for the lab heat, you have used the mass of HCl in grams instead of moles. The correct calculation should be 4.18 * 0.05 * -2.8 + 16.7 * -2.8 = -1.176 kJ.

Next, in your theoretical heat calculation, you have used the heat of formation for HCO3 instead of NaHCO3. The correct value for NaHCO3 is -950.9 kJ/mol. Additionally, you have not taken into account the stoichiometric coefficients in the balanced equation. The correct calculation should be (2*-691.1) + (-239.7) - (2*950.9) = -982.6 kJ/mol.

It is also important to note that the heat of formation values are for standard conditions (25°C and 1 atm), so they may not be accurate for your experimental conditions. It is always best to double check your calculations and use accurate values for your specific experimental conditions.

I would also recommend going back and reviewing the principles of thermochemistry and stoichiometry to ensure a better understanding of the concepts and calculations involved in solving thermodynamics problems. Practice makes perfect, so keep working at it and don't get discouraged!