## rate of consumption sign

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

Emma Li 2C
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Joined: Fri Sep 29, 2017 7:07 am
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### rate of consumption sign

For exercise 15.3 and 15.5, why isn't the rate of reaction of NO2 and the rate of oxygen consumption negative?

Thank you!

Sabrina Dunbar 1I
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### Re: rate of consumption sign

In 15.3, the entire rate law for the reactant should have a negative sign in front of it. However, because we find the change in concentration as final-initial, 320mmol-450mmol=-130mmol. When fully written out, rate=∆concentration/∆t=-(320mmol-450mmol)/20s=+6.5x10^-3. The negative signs cancel out to generate a positive rate overall.

Angel Ni 2K
Posts: 50
Joined: Sat Jul 22, 2017 3:01 am

### Re: rate of consumption sign

The terms themselves imply the sign. If you have a negative rate of consumption, you would be forming the molecule; it doesn't make sense to call it the rate of consumption. The same goes for rate of formation.