Heat of Reaction

Heat of Solution

Purpose: To determine the heat of solution for a solid (NaOH and NH4Cl) dissolving in water.

Background: An endothermic reaction absorbs heat and the surrounding water gets cold and a temperature decrease results. An exothermic reaction gives off heat and the surrounding water absorbs the heat and a temperature increase results.

Materials: Styrofoam cups, Thermometer, Graduated cylinder, Balance, NaOH, NH4Cl

Procedure:

NaOH

1. Measure 20mL of H2O in a graduated cylinder and pour that into the calorimeter. Record the temperature.

2. Add 1 – 2 grams NaOH and record the highest temperature attained. Clean calorimeter.

NH4Cl

1. Measure 30mL of H2O in a graduated cylinder and pour that into the calorimeter. Record the temperature.

2. Add 8-10 grams NH4Cl and record the lowest temperature attained. Clean calorimeter.

Data:

NaOH

Trial #1 Trial #2

Temperature of H2O (T initial)

Average Initial temperature

Grams of NaOH

Average grams NaOH __________________

Highest temperature after mixing (Tfinal)

Average Final temperature

NH4Cl Trial #1 Trial #2

Temperature of H2O (T initial)

Average Initial temperature

Grams of NH4Cl

Average grams of NH4Cl __________________

Lowest temperature after mixing (Tfinal)

Average Final temperature

Analysis:

Calculate the DH for NaOH and NH4Cl. Show complete setup with units for each calculation.

NaOH

q = mCDT (C = 4.184 J/ g oC, 1 gram H2O = 1 mL H2O)

DH = -q/ moles

NH4Cl

q = mCDT (C = 4.184 J/ g oC, 1 gram H2O = 1 mL H2O)

DH = -q/ moles

Conclusion:

1. Determine whether each reaction is endothermic or exothermic. Support your answer (How do you know?).

2. List possible sources of error