Nahco3 And Nahco3

OBJECTIVE
To determine the change of standard Gibbs free energy for the decomposition of sodium hydrogen carbonate (NaHCO3) from the change of standard enthalpy and the change of standard entropy.

THEORY
Free energy is a state function that expresses the spontaneity of a chemical process in term of enthalpy and entropy change of a system under conditions of constant temperature and volume (Hemholtz free energy) and constant temperature and pressure (Gibbs free energy). It is a quantity of non-pressure-and-volume work that a system can perform.

Gibbs free energy also known as Gibbs function.
G = H – TS , where H, S and T denote enthalpy, entropy and temperature respectively.

Gibbs function for a chemical reaction system is based
In this experiment, the heat released/absorbed by decomposition of NaHCO3 can not be measured directly and need to be carried out in two separate experiments in determining the quantities ∆Hᶿ for the reactions of NaHCO3 and Na2CO3.

The reaction are as follow:

2NaHCO3 (s) + H2SO4 (aq)  Na2SO4 (aq) + 2CO2 (g) + 2H2O (l) [1] ∆Hᶿ = Y kJmol-1
Na2CO3 (s) + H2SO4 (aq)  Na2SO4 (aq) +H2O (l) + CO2 (g) [2] ∆Hᶿ = Z kJmol-1
_____________________________________________________________________________________________________
[1] – [2’]
2NaHCO3 (s)  Na2CO3 (s) +H2O (l) + CO2 (g) [3] ∆Hᶿ = X kJmol-1

The enthalpy, H is defined as : H = U + PV
A change in enthalpy s equal to the heat supplied at constant pressure to a system in the casewhere the system does no additional work : dH = dq
For a measurable change, ∆H = qp . The heat released/absorbed by each reaction is calculated by using formula : qp = mCp∆T.

CHEMICALS
Sodium hydrogencarbonate powder, NaHCO3
Sodium carbonate powder, Na2CO3
1M Sulphuric acid, H2SO4

APPARATUS
50mL pipette, thermos, thermometer, 100mL beaker and stopwatch
NaHCO3 with H2SO4
2NaHCO3 (s) + H2SO4 (aq)  Na2SO4 (aq) + 2CO2 (g) + 2H2O (l)

qp = mCp∆T
= (50mL x 1cm3/mL x 1.84g/cm3 x 1kg/1000g) x (1.38kJkg-1K-1) x (28.0-33.0) = + 0.6348 kJ
∆Hᶿ = qp / n
= 0.6348 kJ / (4.4318 g / 84.008 gmol-1)
= 0.6348 kJ / 0.05275 mol
= + 12.034 kJmol-1

b. Na2CO3 with H2SO4
Na2CO3 (s) + H2SO4 (aq)  Na2SO4 (aq) +H2O (l) + CO2 (g) qp = mCp∆T
= (50mL x 1cm3/mL x 1.84g/cm3 x 1kg/1000g) x (1.38kJkg-1K 1) x (35.5-34.0) = - 0.1904 kJ
∆Hᶿ = qp / n
= 0.1904 kJ / (3.3222 g / 105.99 gmol-1)
= 0.1904 kJ / 0.03134 mol
= - 6.077 kJmol-1

∆Hᶿ for the decomposition of NaHCO3 :
2NaHCO3(s)+H2SO4(aq)Na2SO4(aq)+2CO2(g)+2H2O(l) [1] ∆Hᶿ=+12.034 kJmol-1
Na2CO3 (s)+H2SO4(aq)Na2SO4(aq)+H2O(l)+CO2(g) [2] ∆Hᶿ =-6.077 kJmol-1
_____________________________________________________________________________________________________
[1] – [2’]
2NaHCO3 (s)  Na2CO3 (s) +H2O (l) + CO2 (g) [3] ∆Hᶿ = X kJmol-1

∆Hᶿ = X kJmol-1 = [1] – [2’]
= [+12.034kJmol-1] – [+6.077 kJmol-1]
= +5.957