9. Given the following thermochemical equations, determine DH (in kJ) for the re
ID: 693871 • Letter: 9
Question
9. Given the following thermochemical equations, determine DH (in kJ) for the reaction between magnesium and water vapor to form 1.3 moles of MgO. Mg(s) + ½ O2(g) MgO(s) H2(g) + ½ O2(g) H2O(g) Mg(s) + H2O(g) MgO(s) + H2(g) -601.8 kJ -241.82 kJ 10. When ammonium nitrate (NH NOs)(s) is used in explosives, it decomposes to N2(g), 0.(g) and H O(g). Write a balanced reaction equation for the decomposition of ammonium nitrate, and determine the enthalpy (in kJ) of reaction to decompose 40 g of NHNO; using standard enthalpies of formation: solid ammonium nitrate =-366 kJ/mol and water vapor =-242 kJ/mol.
Explanation / Answer
Mg(s) + 1/2O2(g) ----------------> MgO (s) DH = -601.8KJ
H2(g) + 1/2O2(g) ----------------> H2O(g) DH = -241.82KJ substract two equation
(-) (-) (-) (+)
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Mg(s) + H2O(g) ------------> MgO (s) + H2(g) DH = -360KJ >>>answer
10. 2NH4NO3(s) --------------> 2N2(g) + O2(g) + 4H2O(g)
DH rex = DHf products - DHf reactants
= (4*-242 + 2*0 + 0) -(2*-366) = -236KJ/mole >>>>answer
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