Question

3) What role does the balance equation play when determining order and relative rates?

Answer 1

Order is the sum of the powers of the concentration terms in the rate equation. It is an experimental quantity.

There is no role of balanced equation in determining the order of a reaction.

For example for reaction 2A +3B ------> D + 4E reaction,

Rate equation can be written only by carrying out the experiment. Without doing experiment, it is not possible to predict whether rate depends on concentration of given reactants.

Rate may or may not depends on concentration of reactants. This can be identified only after doing experiment. There is no role of balanced equation in determining the order of the reaction.

Role of balanced equation on relative rate:

Rate is the decrease in concentration of reactants or products in a given time interval.

Rate can be expressed in terms of change in concentration of reactants or products. Whether rate is expressed in terms of reactants or products, it should be same. Hence rate is always expressed per mole of the reactants or products.

In determining the relative rate, balanced equation plays an important role.

If balanced equation is wrong, relative rates also become wrong.