when water is combined with magnesium nitride to produce magnesium hydroxide and ammonia gas, is this reaction endothermic or exothermic and why?
Frankly, I don't know; however, you can calculate delta H from this.
Mg3N2 + 3H2O ==> 3MgO + 2NH3
Look up delta Hrxn = (n*delta Hof)products - (n*delta Hof)reactants
The reaction between water and magnesium nitride to produce magnesium hydroxide and ammonia gas is exothermic.
The reason is that when magnesium nitride reacts with water, the bonds between magnesium and nitrogen (in the nitride) are broken, and the bonds between hydrogen and oxygen (in water) are broken. This requires energy input, making the reaction endothermic.
However, when the new bonds are formed between magnesium and hydroxide ions (forming magnesium hydroxide) and between hydrogen and nitrogen (forming ammonia gas), energy is released, making the overall reaction exothermic.
Thus, the energy released during the formation of the new bonds more than compensates for the energy needed to break the initial bonds, resulting in a net release of energy and classifying the reaction as exothermic.
To determine whether the given reaction is endothermic or exothermic, we need to understand the concept of enthalpy and the energy changes that occur during a chemical reaction.
The reaction in question is the combination of water (H2O) with magnesium nitride (Mg3N2), resulting in the formation of magnesium hydroxide (Mg(OH)2) and ammonia gas (NH3).
To determine the energy changes associated with this reaction, we can look at the enthalpies of formation (ΔHf) for the substances involved. Enthalpy of formation is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states.
The balanced chemical equation for the reaction is:
3 Mg3N2 + 6 H2O → 2 Mg(OH)2 + 6 NH3
To evaluate whether the reaction is endothermic or exothermic, we need to compare the enthalpy of the reactants to the enthalpy of the products. If the enthalpy of the products is lower than the enthalpy of the reactants, the reaction is exothermic. Conversely, if the enthalpy of the products is higher than the enthalpy of the reactants, the reaction is endothermic.
Now, to get the enthalpy change for the reaction, we can use the enthalpy of formation values for each compound involved.
Enthalpy of formation values:
ΔHf(Mg3N2) = -156.2 kJ/mol
ΔHf(H2O) = -285.8 kJ/mol
ΔHf(Mg(OH)2) = -924.5 kJ/mol
ΔHf(NH3) = -45.9 kJ/mol
By using the enthalpy values, we can calculate the enthalpy change of the reaction:
Reactants: (3 mol Mg3N2 × ΔHf(Mg3N2)) + (6 mol H2O × ΔHf(H2O))
Products: (2 mol Mg(OH)2 × ΔHf(Mg(OH)2)) + (6 mol NH3 × ΔHf(NH3))
ΔH = (3 × -156.2 kJ/mol) + (6 × -285.8 kJ/mol) - (2 × -924.5 kJ/mol) - (6 × -45.9 kJ/mol)
Simplifying the equation, we have:
ΔH = -468.6 kJ + (-1714.8 kJ) - (-1849 kJ) - (-275.4 kJ)
ΔH = -468.6 kJ - 1714.8 kJ + 1849 kJ - 275.4 kJ
ΔH ≈ -609 kJ
Since the enthalpy change (ΔH) is negative (-609 kJ), indicating that energy is released or liberated, we can conclude that the given reaction is exothermic. It releases energy in the form of heat.
Therefore, when water is combined with magnesium nitride to produce magnesium hydroxide and ammonia gas, the reaction is exothermic.