Write three thermochemical equation needed to calculate delta H for the following reaction:
2Mg(s) + O2(g) = 2MgO
Include delta h values in kJ for each reaction.
Please help!! I don't even know were to start!!
To calculate ΔH (the enthalpy change) for a given reaction, you need to use the concept of Hess's law, which states that the overall enthalpy change of a reaction is equal to the sum of the enthalpy changes of the individual steps in the reaction pathway.
To obtain ΔH for the reaction 2Mg(s) + O2(g) ⟶ 2MgO, we can break it down into three steps:
1. Formation of MgO(s) from its elements:
Mg(s) + 1/2 O2(g) ⟶ MgO(s)
This is the formation reaction of MgO from its constituent elements. The ΔH value for this reaction can be found in thermochemical tables and is typically given as -601.8 kJ/mol.
2. Combustion of magnesium (Mg) to form magnesium oxide (MgO):
2Mg(s) + O2(g) ⟶ 2MgO(s)
This is the given reaction, and we are trying to find ΔH for it.
3. Decomposition of oxygen (O2) into its elements:
1/2 O2(g) ⟶ O(g)
This is the decomposition reaction of oxygen into its constituent atoms. The ΔH value for this reaction can also be found in thermochemical tables and is typically given as +249.2 kJ/mol.
To calculate ΔH for reaction 2, we can use the concept of Hess's law and combine the enthalpy changes of reaction 1 and reaction 3. Since reaction 1 releases energy and reaction 3 requires energy, we subtract the enthalpy change of reaction 3 from that of reaction 1:
ΔH2 = ΔH1 - ΔH3
ΔH2 = -601.8 kJ/mol - (+249.2 kJ/mol)
ΔH2 = -851 kJ/mol
Therefore, the ΔH value for the reaction 2Mg(s) + O2(g) ⟶ 2MgO(s) is -851 kJ/mol.
Note: It is essential to ensure that the stoichiometry of the individual reactions is appropriate for canceling/reacting species.