Magnesium metal reacts with hydrochloric acid according to the following equatio

Question

Magnesium metal reacts with hydrochloric acid according to the following equation:

Mg(s) + 2HCl(aq) ? MgCl2(aq) + H2(g)

To determine the enthalpy change for this reaction, 0.158 g of Mg metal is combined with enough HCl to make 100.0 mL of solution in a coffee-cup calorimeter of negligible heat capacity. The HCl is sufficiently concentrated so that the Mg completely reacts. The temperature of the solution rises from 25.6oC to 32.8oC as a result of the reaction. Find the H degree rxn (in kJ/mol) for the reaction as written. Use 1.00 g/mL as the solution density and the specific heat capacity of the solution = 4.181 J/g oC.

Explanation / Answer

moles of magnesium used=0.158/24

=0.0065833

so the energy released in the reaction=mcT

=100*4.2*(32.8-25.6)

=3024 J

so the enthalpy of the reaction is -3024/(0.0065833)

=-4.59*10^2 kJ/mol

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