Gases react explosively if the heat released when the...

Gases react explosively if the heat released when the reaction begins is sufficient to cause more reaction, which leads to a rapid expansion of the gases. Use bond energies to calculate $\Delta H^{\circ}$ of each of the following reactions, and predict which occurs explosively: (a) $\mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{HCl}(g)$ (b) $\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g) \longrightarrow 2 \mathrm{HI}(g)$ (c) $2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)$

Gases react explosively if the heat released when the reaction begins is sufficient to cause more reaction, which leads to a rapid expansion of the gases. Use bond energies to calculate $\Delta H^{\circ}$ of each of the following reactions, and predict which occurs explosively:
(a) $\mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{HCl}(g)$
(b) $\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g) \longrightarrow 2 \mathrm{HI}(g)$
(c) $2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)$

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Key Concepts

Chain Reactions and Explosions

Explosive reactions often proceed via chain mechanisms, where the energy released from an initial reaction event triggers additional reactions. In gaseous systems, the rapid expansion of gases due to the continuous release of heat can lead to an explosive outcome.

Bond Energies

Bond energies represent the energy required to break a chemical bond and are central to calculating reaction enthalpies. By comparing the energies needed to break bonds in the reactants with the energies released upon forming bonds in the products, one can estimate the overall energy change of a reaction.

Enthalpy of Reaction

The enthalpy change for a chemical reaction is determined by subtracting the total energy released in forming new bonds from the total energy absorbed in breaking the original bonds. This calculation helps in understanding whether a reaction is exothermic or endothermic.

Exothermic Reactions

Exothermic reactions release heat into the surroundings, which can, in certain conditions, further accelerate the reaction. When the released heat is sufficient to overcome activation barriers, the reaction rate can increase dramatically, a behavior that is key to understanding explosive reactions.

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