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# Rate constant cancelling units help.. watch

1. K = mol dm^-3 s^-1 / mol dm^-3 * mol dm^-3

How do you cancel them out? I always get mol^-1 dm^3 s^-1 but the answer on the mark scheme says dm^6 mol^-2 s^-1 and i dont know how to get that? :/
2. (Original post by Nkhan)
K = mol dm^-3 s^-1 / mol dm^-3 * mol dm^-3

How do you cancel them out? I always get mol^-1 dm^3 s^-1 but the answer on the mark scheme says dm^6 mol^-2 s^-1 and i dont know how to get that? :/
it depends on your rate equation. The units of the rate constant depend on the order of the reaction. If it's zero order, your units will be mol dm-3 s-1, but if it's first order it will be s-1 and so on.
3. (Original post by Nkhan)
K = mol dm^-3 s^-1 / mol dm^-3 * mol dm^-3

How do you cancel them out? I always get mol^-1 dm^3 s^-1 but the answer on the mark scheme says dm^6 mol^-2 s^-1 and i dont know how to get that? :/
You seem to be missing a term. That's correct if K (we usually use lower case k) is a second order rate constant.

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