12ICHM151LL THERMOCHEMISTRY Thermochemistry ILI: Heat of Combustion of Magnesium
ID: 507772 • Letter: 1
Question
12ICHM151LL THERMOCHEMISTRY Thermochemistry ILI: Heat of Combustion of Magnesium OBJECTIVES: Further explore quantitative aspects of constant-pressure calorimetry Use Hess's law for indirect determination of reaction enthalpy DISCUSSION: of Hess's law. In this experiment, In the Thermochemistry ll experiment, you tested the validity ofreaction (AHne) you will use this principle to make an indirect determination of the enthalpy for the combustion of magnesium ribbon This reaction releases so much enthalpy that the magnesium metal incandesces at white heat. It will not be practical to measure the reaction enthalpy in your foam cup calorimeter, but you can use law and a combination of known and measurable reactions to indirectly determine the Hess's combustion in of The first of these, reaction (2), is the formation reaction of water, which has a known of standard molar enthalpy value: AH --285.8 kJ.mol Finding the appropriate combination reactions (2) (4) will allow you to use Hess's law for reaction (l) PROCEDURE: Reaction 3: Mg(s 2HCl(aa) MgCla(aa) Halg) before. Measure out 100.0 mL of 1.00M 1. Place a cup inside a 250-mL beaker as into the solution. solution into the cup. Lower the temperature probe 2. weigh a os g sample of magnesium ribbon, and record the mass to the full available precision of the balance. 3. Record the temperature every 20 s. After you have obtained three readings at the same temperature, add the weighed magnesium ribbon to the solution. Stir with a glass rod while the temperature climbs. Once the temperature passes its maximum and starts to drop, suspend data collection. If you can't tell, collect data for s. 4. Dispose of the product solution in the proper waste container. 5. search your data to determine the solution's initial temperature, T, and the maximum temperature, T, Record your T and Ti values on the data sheet. Repeat steps 1-5 using 1.0 g of Mgo instead of Mg ribbon. For easy transfer into the calorimeter, weigh the white powder onto creased weighing paper. Record the Mgo mass on your data sheet to the full available precision of the balance.Explanation / Answer
Calculation for reaction 3 :
Final temperature = 36.9oC
initial temperature = 25.1 oC
temperature difference = 11.8oC
Volume of HCl = 100mL
Mass of HCl = 100gm
Mg+ HCl = 100.546 gm
Heat (q) = 100.546 gm * 4.184 J/gm /oC * 11.8oC = 4964.08 J
enthalphy change = 4964.08 J
Amount = 0.546gm/24g/mol = 0.023 mol
molar enthalpy change = 4964.08 J/ 0.023 mol = 215.83kJ/mol
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Calculation for reaction 4 :
Final temperature = 30.5oC
initial temperature = 24.9 oC
temperature difference = 5.6 oC
Volume of HCl = 100mL
Mass of HCl = 100gm
Mg+ HCl = 101.04 gm
Heat (q) = 101.04 gm * 4.184 J/gm /oC * 5.6oC = 2367.41 J
enthalphy change = 2367.41 J
Amount = 1.04/40g/mol = 0.026 mol
molar enthalpy change = 2367.41 J J/ 0.026 mol = 91.054 kJ/mol
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