On the basis of your experience, predict which of the...

On the basis of your experience, predict which of the following reactions are spontaneous. (a) $\mathrm{CO}_{2}(s) \longrightarrow \mathrm{CO}_{2}(g)$ at $25^{\circ} \mathrm{C}$ (b) $\mathrm{NaCl}(s) \longrightarrow \mathrm{NaCl}(l)$ at $25^{\circ} \mathrm{C}$ (c) $2 \mathrm{NaCl}(s) \longrightarrow 2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g)$ (d) $\mathrm{CO}_{2}(g) \longrightarrow \mathrm{C}(s)+\mathrm{O}_{2}(g)$

On the basis of your experience, predict which of the following reactions are spontaneous.
(a) $\mathrm{CO}_{2}(s) \longrightarrow \mathrm{CO}_{2}(g)$ at $25^{\circ} \mathrm{C}$
(b) $\mathrm{NaCl}(s) \longrightarrow \mathrm{NaCl}(l)$ at $25^{\circ} \mathrm{C}$
(c) $2 \mathrm{NaCl}(s) \longrightarrow 2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g)$
(d) $\mathrm{CO}_{2}(g) \longrightarrow \mathrm{C}(s)+\mathrm{O}_{2}(g)$

Key Concepts

Gibbs Free Energy

Gibbs free energy (?G) is a thermodynamic function that determines whether a reaction can occur spontaneously at constant temperature and pressure. A negative ?G indicates that the reaction proceeds without needing continuous external input of energy, whereas a positive ?G means that the reaction is non-spontaneous under those conditions.

Enthalpy and Entropy

The contributions of enthalpy (?H) and entropy (?S) are fundamental in the calculation of Gibbs free energy, as expressed by the equation ?G = ?H - T?S. Understanding how heat exchange (enthalpy) and the degree of disorder (entropy) change during a reaction is key to predicting whether a reaction will be spontaneous.

Phase Transitions and Stability

Phase changes, such as sublimation, melting, and decomposition, involve alterations in molecular arrangement and energy states, which significantly impact the spontaneity of a reaction. A reaction that involves a change from one phase to another will depend on the balance between the energy required for breaking intermolecular forces and the disorder introduced by the phase change.

Reaction Conditions and Kinetic Factors

While thermodynamics provides insight into the spontaneity of a reaction through free energy calculations, reaction conditions such as temperature and pressure can further influence the overall behavior. Additionally, kinetic factors, like activation energy, determine how quickly a reaction proceeds even if it is thermodynamically favorable.

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