Hess's Law
Data: NaOH solution process
Tinitial =
__________
Tfinal =
__________
Mass of NaOH =
__________
Calculations: NaOH solution process.
1. Calculate the mass of water used to dissolve the NaOH.
2. Calculate the moles of NaOH dissolved.
3. Calculate ∆T.
4. Calculate the total amount of heat gained by the water as the NaOH dissolved.
Heat gained = (mass)(specific heat water)(∆T)
5. Convert the heat gained from J to kJ.
6. Calculate the heat released in kJ per mole of NaOH.
This is the heat of solution per mole of sodium hydroxide.
II. Reaction II: Heat of solution of sodium hydroxide plus heat of
neutralization of sodium hydroxide with hydrochloric acid.
Data: Heat of solution of NaOH + heat of reaction of HCl (aq) + NaOH.
Tinitial =
_________
Tfinal =
_________
Volume of HCl =
_________
Mass of NaOH =
_________
Calculations: Heat of solution of NaOH + heat of reaction of HCl (aq) + NaOH.
1. Calculate the mass of HCl solution used to dissolve and react with the NaOH. Assume a
density of 1 g per mL.
2. Calculate the moles of NaOH used.
3. Calculate ∆T.
4. Calculate the total amount of heat gained by the water as the NaOH dissolved and then
reacted with the HCl.
Heat gained = (mass)(specific heat water)(∆T)
5. Convert the heat gained by the water as the NaOH dissolved and then reacted with the HCl
from J to kJ.
6. Calculate the heat released in this entire process in kJ per mole of NaOH.
This is the heat of solution of one mole of NaOH plus the heat of
neutralization of NaOH and HCl.
III. The heat of reaction for NaOH (aq) + HCl (aq)
Na+(aq) + OH-(aq) +H+(aq) + Cl-(aq) ---> H2O + Na+(aq) + Cl-(aq)
Data: Heat of reaction of NaOH (aq) + HCl (aq)
Tinitial =
_________
Tfinal =
_________
VNaOH =
_________
V HCl =
_________
Method: Heat of reaction of NaOH (aq) + HCl (aq)
1. Calculate the total mass of the combined solutions. Assume a density of 1 g per mL.
2. Calculate ∆T.
3. Determine the number of moles of NaOH used in this reaction.
4. Calculate the total amount of heat released in the neutralization reaction.
Heat gained = (mass)(specific heat water)(∆T)
5. Convert the heat released in the neutralization reaction from J to kJ.
6. Calculate the heat released in this entire process in kJ per mole of NaOH.
This is the heat of neutralization of NaOH and HCl.
Summary Calculations
1. Demonstrate that reaction II is the sum of reaction I and reaction III by adding equation I and
equation III.
2. Determine the sum of the heat released in reaction I and reaction III.
3. Calculate the percent error between the experimental value of reaction II and the sum of
reactions I and III.
4. The accepted value for the heat of solution of NaOH and heat of neutralization (Reaction II)
is 92 kJ/mole NaOH. Calculate the percent error between this value and your experimental value
for reaction II.
5. Cite three sources of error in this experiment.