Final answer:
The reaction rate is calculated by using the change in concentration of reactants or products over time while accounting for the stoichiometric ratios outlined in the balanced chemical equation.
Step-by-step explanation:
To calculate the reaction rate of a chemical process where the ratio of disappearance to appearance of substances is not 1:1, you need to consider the stoichiometry of the balanced chemical equation. For example, consider a reaction where 2 moles of reactant A decomposes to form 1 mole of product B. The rate of disappearance of A is twice as fast as the rate of appearance of B. The average reaction rate can be determined by measuring the concentration of A and B at two different times, t0 and t1, and using the formula: average rate = -(Δ[A])/(Δt) for reactants or average rate = (Δ[B])/(Δt) for products, bearing in mind the stoichiometric coefficients.
In the case where we are dealing with substances that react or form in ratios other than 1:1, the reaction rate must be divided by the stoichiometric coefficient.
For instance, if the disappearance rate of Br- is 3.5 × 10-4 mol L-1 s-1, and the balanced chemical equation indicates that 5 moles of Br- yield 3 moles of Br2, the rate of appearance of Br2 would be calculated by dividing the disappearance rate of Br- by 5/3, according to their stoichiometric relationship.