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Heat of formation of Magnesium oxide

Before Lab
Complete the usual prelab procedure and sample calculations or analysis flowchart or outline, along with the prelab problems. Your analysis flowchart should include each of the chemical equations you must sum together to calculate for MgO and the calculation of the heat capacity Ctotal.

The reaction examined first will be

HCl(aq, 0.5 M) + NaOH(aq, 0.5 M)

H2O(l) + NaCl(aq, 0.25 M)(1)

Using the enthalpy of formation data given in Table 1, below, calculate the molar H° for this neutralization reaction. Convert this value to an enthalpy change, H, for the experiment you will perform, remembering that you must consider the moles of each reactant used in the experiment. Note that the sign of H is very important! Using the calculated value of H and the value of (T2 - T1) measured for reaction (1), you will calculate the heat capacity, Ctotal.

The second reaction examined was

Mg(s) + 2 HCl(0.5 M)

MgCl2(~0.025 M in ~0.45 M HCl) + H2(g) (2)

Using the heat capacity calculated above and the value of (T2 - T1) measured for this reaction, you will calculate its enthalpy change (again, take care with the sign of H). Finally you will convert your H to the molar H in units of kJ mol-1. You will also compare your experimental value with that calculated using the enthalpy of formation data given in Table 1. (The table does not have data for MgCl2 in 0.45 M HCl; use the MgCl2(aq) value.)

The final reaction examined was

MgO(s) + 2 HCl(0.500 M)

MgCl2(~0.08 M in ~0.35 M HCl) + H2O(l) (3)

Again use the heat capacity calculated above and the measurements for reaction (3) to calculate the enthalpy change for this reaction. Finally, you will convert your H to the molar H, and compare your experimental value with that calculated using data given in Table 1.

Now you can use the molar H values calculated for reactions (2) and (3) and the data in Table 1, to calculate the enthalpy of formation of magnesium oxide, i.e. the molar H for the reaction

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