A comparison between the Enthalpy of formation of MgO acquired via a series of reactions and Hess's Law (will they be equivalent?)

Enthalpy of FormationBackgroundThe total heat of system (ΔH°f) is defined as the rouse change associated with the make-up of one mole of a commingle from its elements in their standard states. The major obstacle here, though, is that it is very unvoiced to measure most enthalpies of formations in a standard lab due to the amount of heat or toxic products that argon formed. Thus, in invest to acquire the desired results, one essential use Hess?s Law in which the enthalpy of a series of reactions are measured and added together to give the utmost answer of the enthalpy of formation.

In this situation, to determine the enthalpy of formation for MgO is very difficult in the laboratory (Mg(s) + ½ O2 (g) MgO(s)). But, through a series of reactions and Hess?s Law, the determination of the enthalpy of formation is make possible. Thus, in this investigation, we will see how accurate and precise Hess?s Law can be.

MgO(s) + 2 H+(aq) Mg2+(aq) + H2O(l) ΔH°2 = ?Mg(s) + 2 H+(aq) Mg2+(aq) + H2(g) ΔH°3 = ?+H2(g) + ½ O2(g) H2O(l) ΔH°4 = ?286 kJ/molMg(s) + ½ O2 (g) MgO(s) ΔH°f = ?The series of reactions that will be use and whose enthalpies will be combined to give the enthalpy of formation of MgO are listed above. The first shade, though, has MgO in the reactant send outment, but in the equality above that, MgO is supposed to be in the product side (enthalpy of formation). Thus, the sign for the enthalpy of the first reaction must be switched; if it?s positive, then it becomes negative and vice versa.

Hypothesis:If a series of reactions are used to determine the ΔH°f of MgO, then the experimental value acquired in this investigation should be very close to the accepted value due to Hess?s Law.

Variables:Independent Variables:The Molarity of the Acid usedThe type and amount of the elements usedDependent Variables:The enthalpy of formation of the MgOControl of Variables:Several reactions that have been careful constructed are performed to a lower place special conditions to acquire the desired results.

Materials and MethodMaterials200ml of 3.



0M HClGraduated CylinderMagnesium StripsThermometerStyrofoam Cup w/LidWeighing ScaleMgO powderMethod and ProcedurePart 1: MgO(s) + 2 H+(aq) Mg2+(aq) + H2O(l)1.Take the Styrofoam cup and put 100 ml of 3.0 M HCl in it.

2.Weigh out about one thou of powdered MgO.

3.Make a very small hole in the lid of the Styrofoam cup just big enough for the thermometer to fill through so no heat escapes.

4.Record the initial temperature of the HCl5.Then, place the MgO into the cup and quickly place the lid on it to counteract the heat from escaping6.Pick up the cup and stir it and record the largest temperature reached by the reaction.

Part 2: Mg(s) + 2 H+(aq) Mg2+(aq) + H2(g)1.Repeat every step from Part 1 except use about 0.5 g of Mg metal (strips) instead of the MgO and record the initial and lowest temperatures in the cup.

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