Enthalpy Change of a Chemical Reaction - Calorimetry LaboratoryPurpose – To determine the molar enthalpy for the reaction between magnesium and hydrochloric acid.

Procedure1. Determine and record the mass of the Styrofoam cup calorimeter.

2. Use the graduated cylinder to measure approximately 50 mL of 1.00 mol/L hydrochloric acid. Addthe acid to the calorimeter.

3. Determine and record the mass of the calorimeter and hydrochloric acid.

4. Determine the initial temperature of the hydrochloric acid to the nearest 0.1 °C.

5. Use the steel wool to clean the surface of a 5 cm strip of magnesium strip.

6. Weigh out 0.15 g of Mg.

7. Bend the magnesium wire into a coil.

8. Add the magnesium wire to the hydrochloric acid, quickly place the lid on the cups and insert thethermometer through the hole in the lid.

9. Gently swirl the calorimeter and contents and record the highest temperature reached to the nearest0.1 °C.

10. Discard the reaction mixture in a waste container, rinse and dry the equipment.

11. Repeat the above procedure with 0.25 g of Mg and 0.35 g of Mg.

Data Table:Record observations

Mg(s) + 2HCl(aq) H2(g) + MgCl2(aq)

Mass of calorimeter _________ g

Mass of calorimeter + hydrochloric acid _________ g

Initial temperature of the solution ________ °C

Mass of magnesium strip _________ g

Final temperature of the solution _________°C

Calculations:1. Calculate the heat released into the solution for the 3 reactions, according to:

q(reaction) = mass(contents) * s (contents) * ∆T(use s= 4.184 J/g°C)

3. Find the molar heat of reaction for each experiment in units of Joules / (mole of Mg) by dividing theheat of reaction by the moles of Mg used.

4. Calculate and record the average molar heat of reaction from the three results.

Report:1. The molar heat of reaction is ____________ J/mole of Mg.

2. The theoretical value for heat of reaction of Mg with HCl is –462.5 kJ/ mol Mg. Calculate the percenterror in your experiment.

3. Discuss three sources of errors in the lab