Le zinc se dissout dans une solution d'acide chlorhydrique....

Le zinc se dissout dans une solution d'acide chlorhydrique. L'équation stœchiométrique de cette réaction s'écrit : $$ \mathrm{Zn}(\mathrm{s})+2 \mathrm{H}^{+}(\mathrm{aq})=\mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{H}_2(\mathrm{~g}) $$ Comment peut-on déterminer l'enthalpie de cette réaction, en utilisant les données de l'Annexe I ainsi que les enthalpies de dissolution de $\mathrm{HCl}$ gazeux $\left(-73 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right)$ et du chlorure de zinc solide $\left(-62 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right)$ ?

Le zinc se dissout dans une solution d'acide chlorhydrique. L'équation stœchiométrique de cette réaction s'écrit :
$$
\mathrm{Zn}(\mathrm{s})+2 \mathrm{H}^{+}(\mathrm{aq})=\mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{H}_2(\mathrm{~g})
$$

Comment peut-on déterminer l'enthalpie de cette réaction, en utilisant les données de l'Annexe I ainsi que les enthalpies de dissolution de $\mathrm{HCl}$ gazeux $\left(-73 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right)$ et du chlorure de zinc solide $\left(-62 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right)$ ?

Key Concepts

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the number of steps the reaction is carried out in. This principle allows one to add or subtract the enthalpy changes of different reactions to obtain the overall enthalpy change for a target reaction, even if the reaction occurs in a series of steps.

Enthalpy of Reaction

The enthalpy of reaction is the heat absorbed or released during a chemical reaction at constant pressure. It is a key thermodynamic quantity that can be determined using tabulated enthalpies of formation or enthalpies of dissolution for the substances involved in the reaction.

Enthalpy of Dissolution

The enthalpy of dissolution refers to the heat change associated with the process of dissolving a substance into a solvent. In the context of this problem, the given enthalpy values for the dissolution of gaseous HCl and solid zinc chloride are used as reference data to construct a thermochemical cycle that enables the calculation of the overall reaction enthalpy.

Thermochemical Equations

Thermochemical equations are chemical equations that include the enthalpy change for the reaction. By writing out individual thermochemical equations for processes like dissolution and formation, and then combining them appropriately according to Hess's Law, one can calculate the net enthalpy change for a complex reaction.

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