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Equilibrium pressure refers to the pressure of a gas when a chemical reaction reaches a state where the rates of the forward and reverse reactions are equal.
This means that the amount of reactant turning into product is equal to the amount of product reverting back into the reactant, resulting in no net change in the concentrations of reactants and products over time.
In the case of the decomposition of arsine (\(\mathrm{AsH}_3\)), the equilibrium pressure is the pressure measured in the flask after the system reaches equilibrium. - Initially, only the pressure of pure \(\mathrm{AsH}_3\) is considered, which was \(392.0\) torr. - As the reaction progresses towards equilibrium, this pressure shifts to \(488.0\) torr, which includes the contribution from the formed gas \(\mathrm{H}_2\) as well.Thus, at equilibrium, the pressure of \(\mathrm{H}_2\) is calculated as \(144\) torr, indicating the amount of gas formed as a result of the decomposition reaction reaching a balance.

The equilibrium constant, denoted as \(K_p\), is a central concept in understanding chemical equilibria in gaseous systems.
It is defined based on the partial pressures of the gases involved in the reaction at equilibrium.The relationship for calculating \(K_p\) in a reaction is given by the expression derived from the balanced chemical equation, where the pressures of products are divided by the pressures of reactants.
For the decomposition of \(\mathrm{AsH}_3\), this is expressed as:\[K_p = \frac{(\text{Pressure of } \mathrm{H}_2)^3}{(\text{Pressure of } \mathrm{AsH}_3)^2}\]
In our case:- \(\mathrm{H}_2\) reached an equilibrium pressure of \(144\) torr.- The remaining \(\mathrm{AsH}_3\) pressure is \(296\) torr (calculated as \(392 - 96\) torr).Substituting these values into the equation gives:\[K_p = \frac{144^3}{296^2} = 0.163\] This \(K_p\) value indicates the extent to which a reaction favors the formation of products at equilibrium under given conditions.

A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances.
It usually requires energy input, like heat, light, or electricity, to proceed.In the reaction involving arsine (\(\mathrm{AsH}_3\)), the gas decomposes into solid arsenic (\(\mathrm{As}\)) and hydrogen gas (\(\mathrm{H}_2\)).- The initial compound, \(\mathrm{AsH}_3\), undergoes a chemical change, evidenced by the decrease in its pressure as it loses energy.- The products formed are more stable at the reaction conditions provided, leading to the observed equilibrium of gases in the system.This type of reaction is important in understanding how complex substances can break into simpler components, shifting the balance of reactions and affecting the equilibrium constants and pressures in chemical systems.