## signs

Jasmine Alcantara 3G
Posts: 18
Joined: Wed Sep 21, 2016 2:58 pm

### signs

Why are the average and instantaneous rate negative while you're calculating them? For my PLF worksheet, they're both negative.

Emma_Green_2C
Posts: 21
Joined: Wed Sep 21, 2016 2:57 pm

### Re: signs

If I am understanding your question correctly, I believe the negative sign is used when calculating the rate of the reactant because the concentration of the reactant decreases as it becomes product.

EllisJang2O
Posts: 18
Joined: Wed Sep 21, 2016 2:55 pm

### Re: signs

We only want to deal with positive rates, therefore when calculating rates we use:
R --> P
(instantaneous) RATE = -d[R]/dt = d[P]/dt

Irma Ramos 2I
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### Re: signs

The signs depends on whether or not the rate is for the products or reactants. For products, the rate is positive, and for reactants, the rate is negative.

Angel Gomez 1K
Posts: 36
Joined: Fri Sep 29, 2017 7:04 am

### Re: signs

Wouldn't it depend on what your initial concentrations are? I would think that if you start with more products, they would decrease over time, and your rate for the reverse rxn would be (-) negative. Is this correct?

kaushalrao2H
Posts: 63
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 2 times

### Re: signs

yes, over time, if a reactant is decreasing, then the sign on the rate expression would be negative. however, if a reactant is increasing over time, then the sign on the rate expression would be positive.

Christina Bedrosian 1B
Posts: 33
Joined: Fri Sep 29, 2017 7:05 am

### Re: signs

we dont want to be talking about "negative" rates so we add the negative when talking about the rates of the reactants since they are decreasing and their rate would normally be negative (adding the negative makes it positive, which we want, this also represents rate of products)

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