Question

For the reaction $A+B\to C$; starting with different initial concentrations of A and B, the initial rate of reaction were determined graphically in four experiments. Find the rate of reaction ($r$).

S.No.	[A] M (Initial conc.)	[B] M (Initial conc.)	rate (M $se{c}^{-1}$)
1	$1.6\times {10}^{-3}$	$5\times {10}^{-2}$	${10}^{-3}$
2	$3.2\times {10}^{-3}$	$5\times {10}^{-2}$	$4\times {10}^{-3}$
3	$1.6\times {10}^{-3}$	${10}^{-1}$	$2\times {10}^{-3}$
4	$3.2\times {10}^{-3}$	${10}^{-1}$	$8\times {10}^{-3}$

• A. $r=k\left[A{]}^2\right[B{]}^2$
• B. $r=k\left[A{]}^2\right[B]$
• C. $r=k\left[A\right][B{]}^2$
• D. $r=k\left[A\right]\left[B\right]$

Answer 1

The correct option is B $r=k\left[A{]}^2\right[B]$

Order

$A+B\to P$

$r=k[A{]}^x[B{]}^y$

$\therefore order=x+y$

We first keep the concentration of one of the reactants constant and by changing the concentration of the other reactant, we see it's effect on the rate of reaction and establish a relation.

For example in this when the concentration of B is kept constant and when the concentration of A is doubled, the rate becomes 4 times the initial rate.

So, the power of A should be two so that doubling the concentration of A will make the reaction four times faster.

We follow the same procedure with the other reactants and establish the relationship in the same way.