Reaction A) Mg(s) + 2HCl (aq) --> H2(g) + MgCl2 (aq) Reaction B). MgO(s) + 2HCl

Question

Reaction A)

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

Reaction B).

MgO(s) + 2HCl (aq) --> H2O(l) + MgCl2 (aq)

Determination of Enthalpy of Reaction for Reaction C Reaction (C) MgO(s) + H_2(g) rightarrow Mg(s) + H_2O(l) Hess' Law Calculation of Delta H_c (Use "best" or average values.) Show combine equation A and B to obtain equation C. Show by a clear set-up how to combine the enthalpies of reactions A and B to obtain Delta H_c Delta H_c = _____ kJ/mol Calculate the standard enthalpy of reaction for Reaction c, Delta H_c degree, using the standard molar enthalpies of formation found in Appendix C in Ebbing. Show your work below. Assuming Delta H_c degree is the theoretical value and Delta H_c is experimental value, calculate the percent error. Show work below. Thinking about the value of Delta H_c and the chemicals involved in Reaction C, does reaction C seem feasible as a way to obtain pure Mg metal from magnesium oxide? Why or Why not? Suppose some of the Mg did not completely react when you were collecting data on Reaction A. a. How would this affect the calculated value of Delta H_A? Describe the expected change in the value. b. How would this affect the calculated value of Delta H_c? Describe the expected change in the value.

Explanation / Answer

Ans 1.

According to the Hess's Law of constant heat summation , the total enthalpy of the reaction is the net sum of all the changes or steps that have been involved to produce the final product .

So the reaction C can be obtained if reaction A is subtracted from reaction B .

MgO(s) + 2HCl (aq) --> H2O(l) + MgCl2 (aq) - [Mg(s) + 2HCl (aq) --> H2(g) + MgCl2 (aq) ]

=MgO (s) + H2(g) = Mg(s) + H2O (l)

The enthalpy of B reaction is -151 KJ and that of reaction A is -466.85 KJ

So the enthalpy of reaction C will be -151 - (-466.85) = 315.85 KJ

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