Chemistry · Chemical Kinetics · NEET
Order of a reaction is just the sum of the powers of the concentration terms written in the rate law. If Rate = k[A]^x[B]^y, then order = x + y. The power x is the order with respect to A, and y is the order with respect to B. The total, x + y, is the overall order. Simple rule: look at the rate law, add the powers, that number is the order.
You cannot read the order from the balanced chemical equation. Order is found only by experiment, from the rate law. First get the rate law (from experimental rate-vs-concentration data), then add the powers of the concentration terms. Example: Rate = k[A]^2[B] has order = 2 + 1 = 3. For NEET, most questions give you the rate law directly, so you just add the powers.
The order with respect to one reactant IS the power on that reactant in the rate law. The overall order is the SUM of all those powers. So in Rate = k[A]^2[B]^1: order in A = 2, order in B = 1, and overall order = 3. Do not confuse a single power (order in one reactant) with the total (overall order).
Yes. Order is experimental, so it can be 0, 1, 2, 3, or even a fraction like 1/2 or 1.5. A zero order reaction means the rate does not depend on the reactant concentration at all (Rate = k[A]^0 = k). Fractional orders happen in complex reactions with multi-step mechanisms. This is different from molecularity, which is always a whole number.
Because most reactions happen in several steps, not in one step. The balanced equation only shows the overall change, not how the reaction actually proceeds. The rate depends on the slowest step (rate-determining step), which the equation does not show. So the powers in the rate law (and therefore the order) must come from experiments, not from the coefficients in the equation. This is a very common NEET trap.
It is the power on that particular reactant in the rate law. If Rate = k[A]^2[B], the order with respect to A is 2 and with respect to B is 1. It tells you how sensitive the rate is to changing that one reactant. If you triple [A], the rate changes by 3^2 = 9 times (because A is second order). The overall order (2 + 1 = 3) uses all reactants together.
For a certain reaction, the rate = k[A]^2[B]. When the initial concentration of A is tripled keeping the concentration of B constant, the initial rate would:
The correct option for the rate law that corresponds to an overall first order reaction is:
For a certain reaction R -> Product, the plot of concentration [R] versus time is a straight line with a constant negative slope. The order of the reaction is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The order of a reaction is the sum of the powers of the concentration terms in the experimentally determined rate law. For Rate = k[A]^x[B]^y, the overall order = x + y.
Yes, the order with respect to a single reactant can be negative (like -1/2), which means increasing that reactant actually slows the reaction. The overall order is still the sum of all the powers.
No. Order is found by experiment, so it can be 0, 1, 2, 3, or a fraction like 1/2 or 1.5. Fractional orders appear in complex multi-step reactions.
Order is experimental and can be zero, fractional, or negative; it is the sum of powers in the rate law. Molecularity is theoretical, always a whole number (1, 2, or 3), and applies only to a single elementary step.
Write the rate law, then add up the powers of all the concentration terms. Example: Rate = k[A]^2[B] gives overall order = 2 + 1 = 3.
