\(\therefore \) Conc. after \(20\,min\) (two half lives) \(=\,2.5\,mol\,L^{-1}\)
Now, \(k\, = \,\frac{{0.693}}{{{t_{1/2}}}}\, = \,\frac{{0.693}}{{10\,\min }}\)
or \(0.0693\,min^{-1}\)
\(\therefore \) rate \(=\,k\times \) [reactant]
\(=\,0.0693\times 2.5\,\,mol\,L^{-1}\,min^{-1}\)
| No | $[A_2]\, M$ | $[B_2]\, M$ | rate of reaction |
| $1.$ | $0.1\,M$ | $0.1\,M$ | $1.6 \times {10^{ - 4}}$ |
| $2.$ | $0.1\,M$ | $0.2\,M$ | $3.2 \times {10^{ - 4}}$ |
| $3.$ | $0.2\,M$ | $0.1\,M$ | $3.2 \times {10^{ - 4}}$ |