Final answer:
The decomposition of XY being a second order reaction implies the reaction rate is proportional to the square of the concentration. The given rate constant is used with the squared concentration to calculate the instantaneous rate of decomposition for the substance in question.
Step-by-step explanation:
The decomposition of XY is a second order reaction, which means that the rate of reaction depends on the concentration of XY squared. The rate constant given for this reaction, 7.02×10-3 m-1s-1, is used in the rate expression to calculate the instantaneous rate of the reaction at a given concentration of XY.
To find the instantaneous rate of decomposition of a substance like acetaldehyde in a second order reaction, we use the formula: rate = k [XY]2. Given a rate constant k and a concentration of XY, one would square the concentration, multiply by the rate constant, and obtain the decomposition rate.
For example, if the decomposition of acetaldehyde has a rate constant of 4.71 × 10-8 L mol-1 s-1 and the concentration is 5.55 x 10-4 M, then the instantaneous rate is calculated as (4.71 × 10-8 L mol-1 s-1) × (5.55 x 10-4 M)2.