I had a problem in which I had to work out the standard enthalpy of formation for MgBr(s)…assuming it exits. I've done that using various bits of given data and got a value of –93.5kJmol^-1…not sure if the actual answer is relevant to my question. Anyway, how can I decide what implications my answer will have on standard entropy of formation and the standard Gibbs function of formation of MgBr? My data book gives me values for MgBr2 but not MgBr. Essentially I'm trying to decide if MgBr(s) will be stable with respect to metallic Mg and liquid Br. Any ideas?

There is no compound MgBr.

I am aware of that MgBr doesn't exit. The question is hypothetical. I worked out my answer above using hypothetical information. I need to know if my hypothetical reaction is stable or unstable...it doesn't matter.

To determine the stability of a hypothetical reaction involving the formation of MgBr(s), you can consider the stoichiometry and the thermodynamic parameters such as the standard enthalpy of formation (ΔH°f), standard entropy of formation (ΔS°f), and standard Gibbs free energy of formation (ΔG°f).

Since there is no specific value available for MgBr in your data book, we can make some assumptions based on the data available for MgBr2 and the stoichiometry of the reaction.

First, let's understand the hypothetical reaction you are considering:

Mg(s) + Br2(l) → MgBr(s)

To determine the stability of MgBr(s) with respect to the elemental forms, you need to compare the standard Gibbs free energy change (ΔG°) for the reaction to zero.

ΔG° = ΔH° - TΔS°

If ΔG° is negative, it indicates that the formation of MgBr(s) is thermodynamically favored and the compound is likely stable. If ΔG° is positive, it suggests that the formation of MgBr(s) is not thermodynamically favored, and the compound may be unstable.

Based on the hypothetical value you calculated for the standard enthalpy of formation (ΔH°f) for MgBr(s) as -93.5 kJ/mol, you have a piece of relevant information. However, without the standard entropy of formation (ΔS°f) for MgBr(s), you cannot make a definite conclusion about stability. To evaluate the stability, you would require the entropy of formation of MgBr(s) or other thermodynamic parameters, such as the entropy of the elements involved.

Additionally, if your data book provides information on the standard enthalpy and entropy of formation for MgBr2, you could use that information along with stoichiometry to estimate the stability of MgBr(s) under standard conditions. However, this would be an approximation and not a direct measurement for MgBr(s).

Ultimately, without specific values for the standard entropy of formation or additional thermodynamic data, a conclusive determination regarding the stability of MgBr(s) cannot be made.