3. ENTHALPY (HEAT) OF NEUTRALIZATION
OF AN ACID-BASE REACTION
By : Dr. Robert D. Craig, Ph.D.
Enthalpy of neutralization: energy released per
mole of water formed in an acid-base reaction –
an “exothermic” property

4. ENTHALPY (HEAT) OF NEUTRALIZATION
OF AN ACID-BASE REACTION
Enthalpy of neutralization: energy released per
mole of water formed in an acid-base reaction –an
“exothermic” property
The negative sign is a result of the heat which is lost
by the system to the surroundings
The reaction of a strong acid with a strong base is a
exothermic reaction that produces water and heat
as products

5. These acids are dangerous

6. ENTHALPY (HEAT) OF NEUTRALIZATION
OF AN ACID-BASE REACTION
H3O+ (aq) + OH- (aq)  2 H2O (l) + heat

7. Secondary caution as well
• Acid to the Water!
• Why add the acid to the water? Because the
same general concept described above applies
when you're mixing an acid or a base to water.
A base is the opposite of an acid and they are
corrosive for different reasons

8. ENTHALPY (HEAT) OF NEUTRALIZATION
OF AN ACID-BASE REACTION
Enthalpy change, Hn
=
-specific heat (H20) x combined massed (Acid -
Base) x DT (H20)

9. This will be done for two acids
Page 296 see data sheet
HCl + NaOH
HNO3 + NaOH

10. Acid base pair number one
• HCl + NaOH
Clean two 250 mL Erlenmeyer flasks with
soap, then rinse and drain. Repeat this until
they drain cleanly without leaving droplets
adhering to the sides, using purified water for
a final rinse.

11. pair number one
• Clean and dry the calorimeter with a towel.
Make sure it doesn't leak. From the solutions
available in the laboratory, rinse one of the
Erlenmeyer flasks with a few mL of 0.500 M
HCl and then drain. Rinse the other flask with
a few mL of 0.500 M NaOH and drain. Label
the flasks to avoid confusion

12. Becareful!!!!!!!50x
• To obtain an accurate temperature
measurement, it is essential that the
thermometer bulb be completely emersed in
the solution. If reaching thermal equilibration
takes a long time, you may wish to dry off the
thermometer and recheck the acid
temperature before the final mix

13. Be careful!!!! 50x
• If the two temperatures differ a bit before
mixing, take the initial mixed solution
temperature to be the average of the acid and
base temperatures. Finally, carefully pour the
base into the acid, stir gently with the
thermometer, and record the exact time of
mixing.

14. Acid base pair number two
• HNO3 + NaOH
• Please redo the same procedure as you did for
• HCl + NaOH
•

15. Last sentence
• Enthalpy change, Hn is generally expressed
in units of kJ/mol of water that forms from the
reaction.
• The mass (grams) of the solution equal the
combined masses of the acid and base
solution (this is important!!!!)