The SN2 reaction of RBr with N3- is first order in each reactant. In methanol an initial rate of 3.0 x 10^-9 M s^-1 is measured at [RBr] = 0.020 M and [N3-] = 0.050 M. The rate constant is 4.0 x 10^4 times larger in DMF at the same temperature. The initial rate in DMF at [RBr] = 0.010 M and [N3-] = 0.20 M is

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The SN2 reaction of $RBr$ with $N X_{3} X^{-}$ is first order in each reactant. In methanol an initial rate of $3.0 \times 1 0^{- 9} M s^{- 1}$ is measured at $[RBr] = 0.020 M$ and $[N X_{3} X^{-}] = 0.050 M$ . The rate constant is $4.0 \times 1 0^{4}$ times larger in DMF at the same temperature. The initial rate in DMF at $[RBr] = 0.010 M$ and $[N X_{3} X^{-}] = 0.20 M$ is

In methanol

k = 3.0 \times 1 0^{- 9} / (0.020 \times 0.050) = 3.0 \times 1 0^{- 6} L mo l^{- 1} s^{- 1}

. In DMF

k = 4.0 \times 1 0^{4} \times 3.0 \times 1 0^{- 6} = 0.12 L mo l^{- 1} s^{- 1}

. The rate is

0.12 \times 0.010 \times 0.20 = 2.4 \times 1 0^{- 4} M s^{- 1}