Question

A reaction is first order in A and second order in B.

1. Write the differential rate equation.
2. How is the rate affected on increasing the concentration of B three times?
3. How is the rate affected when the concentrations of both A and B are doubled?

Answer 1

$(i)$ The differential rate equation will be

$-\frac {d[R]}{dt }= k[A][B]^2$

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$(ii)$ If the concentration of B is increased three times, then

$-\frac {d[R]}{dt }= k[A][3B]^2$

= $9. k[A][B]^2$

Therefore, the rate of reaction will increase 9 times.

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$(iii)$ When the concentrations of both A and B are doubled,

$-\frac {d[R]}{dt} = k[A][B]^2$

= $k[2A][2B]^2$

= $8. k[A][B]^2$

Therefore, the rate of reaction will increase 8 times.