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# Rate = change in property / time question watch

1. Hi there,

I've read that the the unit for rate is always mol dm-3 s-1 however, rate can be calculated with rate = change in property / time; for example:

rate = volume of gas produced / time

This gives the unit of rate = cm3 s-1 which is clearly does not correspond to mol dm-3 s-1

:s

Can anyone help me/clarify on this, please?
Thanks
2. Rate doesn't have to be mol dm-3 s-1, but will be when measuring change in conc. per second, which is very common.

If you are measuring gas production, it makes much more sense to use cm3 s-1 and it is perfectly fine to do so.
3. (Original post by Pigster)
Rate doesn't have to be mol dm-3 s-1, but will be when measuring change in conc. per second, which is very common.

If you are measuring gas production, it makes much more sense to use cm3 s-1 and it is perfectly fine to do so.
Oh, because my CGP revision guide and on chemguide [http://www.chemguide.co.uk/physical/...s/orders.html] it says the units for rate are mol dm-3 s-1...

However, if I was to convert it into mol dm-3 s-1 is it possible to convert from let's say, g s-1 from "rate = mass change / time" to mol dm-3 s-1?

I had a think and this is how I'd do it:

1. Convert the mass change, in grams, into g dm-3 by dividing the mass change of solid by the volume of acid I used

2. Convert g dm-3 into mol dm-3 by dividing g dm-3 by the Mr

3. Convert mol dm-3 into mol dm-3 s-1 by dividing it by time elapsed of the reaction

Is that mathematically right?
4. Seems fair.
5. Hmm.. try watching these 4 minutes videos https://www.youtube.com/watch?v=419NFQwPt9c to better grasp the rr

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