Table 2: The temperature change during the reaction of Hydrochloric acid and Sodium hydrogen Carbonate
Graph 1: The temperature change during the reaction of Hydrochloric acid and Sodium Hydrogen Carbonate
Table 3: The volume of HCL, the mass of weighing bottle & Na2CO3 and mass of Na2CO3 added
Table 4: The temperature change during the reaction of Hydrochloric acid (HCL) and Sodium Carbonate (Na2CO3)
Graph 2: The temperature change during the reaction of Hydrochloric acid (HCL) and Sodium Carbonate (Na2CO3)
Calculations:
Part 1: HCl + NaHCO3 reaction
Change in temperature (ΔT):
ΔT = 18.2 °C – 28.0 °C
ΔT = -9.85 ± 1 °C
Q = mc(ΔT)
Q = (-9.8 °C)(4.18 J/g°C)(100.5 g)
Q = 4116.8 J
Q ≈ - 4.12 kJ
Sign of Q must be opposite with the sign of delta H. Therefore, Q = 4.12 kJ.
Mol NaHCO3 = 14.08 g NaHCO3 ( = 0.167 mol ≈ 0.17 mol NaHCO3
ΔH = = 24.23 kJ mol-1
Part 2: HCl + Na2SO3 reaction
Change in temperature (ΔT):
ΔT = 34.1 °C – 24.2 °C
ΔT = 9.9 ± 1 °C
Q = mc(ΔT)
Q = (9.9 °C)(4.18 J/g°C)(100.5 g)
Q = 4158.891 J
Q ≈ 4.16 kJ
Sign (charge) of Q must be opposite with the sign (charge) of delta H.
Therefore, Q = -4.16 kJ.
Mol Na2SO3 = 8.08 g Na2SO3 ( = 0.076 mol ≈ 0.08 mol Na2SO3
ΔH = = - 5.2 kJ mol-1
Enthalpy change calculation:
2NaHCO3 (s) ➔ Na2CO3 (s) + H2O (l) + CO2 (g) (targeted equation)
HCl (aq) + NaHCO3 (s) ➔ NaCl (g) + H2O (l) + CO2 (g) ΔH = 24.23 kJ mol-1
Na2CO3 + 2HCl ➔ 2NaCl + H2O + CO2 ΔH = -52 kJ mol-1
2HCl (aq) + 2NaHCO3 (s) ➔ 2NaCl (g) + 2H2O (l) + 2CO2 (g) ΔH = 2(24.23 kJ mol-1)
2NaCl (g) + H2O (l) + CO2 (g) ➔ Na2CO3 (s) + 2HCl (aq) ΔH = 52 kJ mol-1
-
2NaHCO3 (s) ➔ Na2CO3 (s) + H2O (l) + CO2 (g)
-
ΔH = 48.46 + 52 = 100.46 kJ mol-1
Conclusion and Evaluation:
Percent error = 86.9 % ≈ 87 % error
Our result is very different from the accepted value of 771 kJ mol-1. I got 100.46 kJ mol-1 as our final result. Since I have a high percentage error of 87%, I came up with some random errors that could have occurred throughout our experiment:
I have to use an analogue thermometer and I have to open the cup to check the temperature so the reaction might not have the accurate result it is affected by the surroundings. The heat might have spread out to the atmosphere around it when I opened the cup to check the temperature in the second experiment. In the first one, the temperature might be affected by the heat from the surroundings and it couldn’t reach the coolest point. Next time, I should use an electric probe (digital thermometer) to minimize the heat loss or heat gain to/from the surroundings. Another thing that has could gone wrong is that throughout the experiment, I put the substance in the acid bit by bit and I moved the cup in circular motions a lot; that could be an error. Because the acid didn’t have the enough amount of sodium to react so the results were not very accurate.