Explain the fact that a small amount of Nal catalyzes the general reaction
`R - CI + R ' - O^(Theta) Na to R - O R + NaCI`
With `I^(-) ` ion the overall reaction occurs in two steps each of which is faster than the uncatalyzed reaction .

Explanation

Step 1
`R- CI + I^(-) to R - I + CI^(Theta)`
This step is faster because `I^(-)` a soft base has more nucleophilicity than `OR^(-)` a hard base
Step 2
`R- I - R' O^(Theta) to R - O - R + I`
This step is faster because `I^(-)` is a better leaving group than `CI^(-)`