Answer: option D. 4.5 seconds.
Explanation:
The equilibrium reaction is H₂O ⇄ H₂ + O₂
The chemical equilibrium is a dynamic one. Two reactions are happening symultaneously: the forward reaction (H₂O → H₂ + O₂) ,to the right, and the reverse reaction (H₂O ← H₂ + O₂), to the left. At equilibrium both reactions have the same rate, which makes that the total, measurable quantity of reactants and products remain constant.
In the figure you see:
- The vertical axis measures concentration.
- The horizontal axis measures time (seconds).
- The two blue lines, the concentrations of H₂ and O₂, become flat (reach a zero slope) between 4 and 5 seconds.
- The red line, the concentration of H₂O, becomes flat, also, between 4 and 5 seconds.
- Hence, the concentrations of the reactant and the products do not change after that time meaning that the reaction has reached the equilibrium at about 4.5 seconds.
