Standars enthalpy
Mg(OH)2 + H2SO4 = MgSO4 + 2 H2O
delta Hrxn = (sum delta H products)-(sum delta H reactants).
Look these values up in a set of tables (one probably is in your text), substitute and solve.
The standard enthalpy change of a reaction, represented as ΔH°, is the heat energy exchanged between the system and the surroundings when the reaction occurs at constant pressure and temperature. It indicates whether a reaction is endothermic (absorbs heat) or exothermic (releases heat).
To calculate the standard enthalpy change of a reaction, you need to know the standard enthalpy of formation (ΔH°f) for each compound involved. The standard enthalpy of formation is the energy change associated with the formation of one mole of a compound from its elements in their standard states.
In the given reaction:
Mg(OH)2 + H2SO4 -> MgSO4 + 2 H2O
To calculate the standard enthalpy change, first write the balanced equation for the reaction:
Mg(OH)2 + H2SO4 -> MgSO4 + 2 H2O
Next, find the standard enthalpy of formation (ΔH°f) for each compound involved. You can find these values in tables or chemical databases.
- ΔH°f for Mg(OH)2: -924.2 kJ/mol
- ΔH°f for H2SO4: -814.2 kJ/mol
- ΔH°f for MgSO4: -1374.0 kJ/mol
- ΔH°f for H2O: -285.8 kJ/mol
Now, calculate the standard enthalpy change (ΔH°) by using the following equation:
ΔH° = Σ(n ΔH°f products) - Σ(n ΔH°f reactants)
Σ represents the sum, n represents the stoichiometric coefficient of each compound.
Substituting the values into the equation:
ΔH° = [1 × (-1374.0 kJ/mol)] + [2 × (-285.8 kJ/mol)] - [1 × (-924.2 kJ/mol)] - [1 × (-814.2 kJ/mol)]
Simplifying the equation:
ΔH° = -1374.0 kJ/mol - 571.6 kJ/mol + 924.2 kJ/mol + 814.2 kJ/mol
ΔH° = -207.2 kJ/mol
Therefore, the standard enthalpy change (ΔH°) for the reaction Mg(OH)2 + H2SO4 -> MgSO4 + 2 H2O is -207.2 kJ/mol.