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Malcolm Sargeant

hot pack experiment: calcium chloride vs magnesium chloride

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$\ce{MgCl2}$ formation enthalpy is for $\ce{Mg(s) + Cl2(g) -> MgCl2(s)}$.

Its hydration enthalpy is for $\ce{Mg^2+(g) + 2 Cl-(g) ->[H2O]Mg^2+(aq) + 2 Cl-(aq)}$

Its lattice formation enthalpy is for $\ce{Mg^2+(g) + 2 Cl-(g) ->MgCl2(s)}$

Its dissolution enthalpy is for $\ce{MgCl2(s) -> Mg^2+(g) + 2 Cl-(g) ->[H2O]Mg^2+(aq) + 2 Cl-(aq)}$

For the heat pack, the dissolution enthalpy is what you need.

Highly negative salt formation enthalpy means they is highly negative lattice formation enthalpy too, what increases value of salt dissolution enthalpy and decreases released heat.

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