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

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

These acids are dangerous

ENTHALPY (HEAT) OF NEUTRALIZATION OF AN ACID-BASE REACTION

H3O+ (aq) + OH- (aq) 2 H2O (l) + heat

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

ENTHALPY (HEAT) OF NEUTRALIZATION OF AN ACID-BASE REACTION

Enthalpy change, DHn

= -specific heat (H20) x combined massed (Acid -Base) x DT (H20)

This will be done for two acids

Page 296 see data sheetHCl + NaOH HNO3 + NaOH

Acid base pair number one

• HCl + NaOHClean 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.

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

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

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.

Acid base pair number two

• HNO3 + NaOH

• Please redo the same procedure as you did for• HCl + NaOH •

Last sentence

• Enthalpy change, DHn 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!!!!)