Hess's Law Lab
Hess’s Law and the Molar Enthalpy of Combustion for Magnesium
Purpose: The purpose of the lab ultimately is to find the molar enthalpy of magnesium. This is done by finding the enthalpy changes of reactions (2) and (3). The enthalpy changes of reactions (2) and (3) along with the enthalpy change given for reaction (4) can be used to arrive at a value of the molar enthalpy of combustion of magnesium by using Hess’s Law.
Hypothesis: By using Hess’s law to calculate the molar enthalpy of combustion using experimentally determined enthalpy change values (from reactions (2) and (3)) it is believed that the final calculated value will be similar to the accepted molar enthalpy of combustion of magnesium being 611kJ/mol. This should be the case because …show more content…
Obtain and set up a simple calorimeter. Add 100 mL of 1.00 mol/L HCL(aq) to the calorimeter using a 100 mL graduated cylinder. On the data table created in the first step, take note of and record the initial temperature of HCL(aq). Collect no more than 0.80 g of MgO(s) powder. Record the mass on the data table. A group member should then add MgO(s) powder to the calorimeter containing HCL(aq). Make sure to swirl gently. After a certain time when the temperature no longer rises, record the highest temperature reached. Dispose of the solution as directed by teacher’s instructions before commencing part 2 of the lab.
Part 2 (Determining the enthalpy change of Reaction 3)
Create a data table to record the mass and temperature data on (exactly as first step in part 1). Using a graduated cylinder, add 100 mL of 1.00 mol/l HCL(aq) to the simple calorimeter Record the initial temperature of HCL(aq) on the data …show more content…
The enthalpy changes of reactions (2), (3), and (4) were added. However before that, equations were rearranged. The thermochemical equation for reaction (2) was reversed with the products becoming the reactants and reactants becoming the products. By doing this, the thermochemical equation for reaction (1) can be arrived at. Then simply add the enthalpy changes. Essentially, since this lab is carried out in numerous individual steps, the molar enthalpy change of combustion of magnesium is equal to the sum of the enthalpy changes (values obtained from individual steps). By using Hess’s law, the molar enthalpy of combustion value for magnesium obtained for the thermochemical equation that corresponds to reaction (1) is -618.55
Purpose: The purpose of the lab ultimately is to find the molar enthalpy of magnesium. This is done by finding the enthalpy changes of reactions (2) and (3). The enthalpy changes of reactions (2) and (3) along with the enthalpy change given for reaction (4) can be used to arrive at a value of the molar enthalpy of combustion of magnesium by using Hess’s Law.
Hypothesis: By using Hess’s law to calculate the molar enthalpy of combustion using experimentally determined enthalpy change values (from reactions (2) and (3)) it is believed that the final calculated value will be similar to the accepted molar enthalpy of combustion of magnesium being 611kJ/mol. This should be the case because …show more content…
Obtain and set up a simple calorimeter. Add 100 mL of 1.00 mol/L HCL(aq) to the calorimeter using a 100 mL graduated cylinder. On the data table created in the first step, take note of and record the initial temperature of HCL(aq). Collect no more than 0.80 g of MgO(s) powder. Record the mass on the data table. A group member should then add MgO(s) powder to the calorimeter containing HCL(aq). Make sure to swirl gently. After a certain time when the temperature no longer rises, record the highest temperature reached. Dispose of the solution as directed by teacher’s instructions before commencing part 2 of the lab.
Part 2 (Determining the enthalpy change of Reaction 3)
Create a data table to record the mass and temperature data on (exactly as first step in part 1). Using a graduated cylinder, add 100 mL of 1.00 mol/l HCL(aq) to the simple calorimeter Record the initial temperature of HCL(aq) on the data …show more content…
The enthalpy changes of reactions (2), (3), and (4) were added. However before that, equations were rearranged. The thermochemical equation for reaction (2) was reversed with the products becoming the reactants and reactants becoming the products. By doing this, the thermochemical equation for reaction (1) can be arrived at. Then simply add the enthalpy changes. Essentially, since this lab is carried out in numerous individual steps, the molar enthalpy change of combustion of magnesium is equal to the sum of the enthalpy changes (values obtained from individual steps). By using Hess’s law, the molar enthalpy of combustion value for magnesium obtained for the thermochemical equation that corresponds to reaction (1) is -618.55