Moderators: Chem_Mod, Chem_Admin

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


Postby Jasmine Alcantara 3G » Wed Feb 22, 2017 6:28 pm

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

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

Re: signs

Postby Emma_Green_2C » Wed Feb 22, 2017 6:42 pm

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.

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

Re: signs

Postby EllisJang2O » Sun Feb 26, 2017 5:21 pm

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

Postby Irma Ramos 2I » Fri Feb 23, 2018 4:02 pm

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

Postby Angel Gomez 1K » Fri Feb 23, 2018 5:27 pm

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?

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

Re: signs

Postby kaushalrao2H » Fri Feb 23, 2018 6:45 pm

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

Postby Christina Bedrosian 1B » Tue Feb 27, 2018 10:03 pm

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)

Return to “Kinetics vs. Thermodynamics Controlling a Reaction”

Who is online

Users browsing this forum: No registered users and 2 guests