## rate constants

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Fdonovan 3D
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### rate constants

Are rate constants always positive? And if so why is this the case?

Jonathan Gong 2H
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### Re: rate constants

Rate constants, k, should be positive since they relate given concentrations with the rate of a reaction, which will always be positive. But, if you are considering graphs, a plot of a 1st or 0 order reaction will have a slope of -k, while a plot of a 2nd order reaction will have a slope of +k.

lilymayek_1E
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Joined: Sat Aug 17, 2019 12:16 am

### Re: rate constants

the rate constant (which is k) should always be positive; you can think of a rate as always positive because k (a proportion between concentrations) is positive, and rate can be presented as K[R]^n, which must be positive as negative concentration or proportions cannot exist.
on a graph of a first-order reaction, the slope is negative, but we have to add a negative sign to the overall rate to accommodate for this downward slope (the rate itself isn't negative)

Abigail_Hagen2G
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### Re: rate constants

Rate constants are always positive because concentrations are always positive.

205405339
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### Re: rate constants

rate constants are always positive and don't have units

Joanne Lee 1J
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### Re: rate constants

Yes, rate constants are always positive because they represent concentration and concentration has to always be positive.

Louise Lin 2B
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### Re: rate constants

yes rate constants are always positive because even when reactions slow down or reverse, the rate from product to reactant is still moving forward, making the rate constant positive.

aishwarya_atmakuri
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### Re: rate constants

Yes, rate constants are always positive because they represent concentration which is based on mass (always positive).

rabiasumar2E
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### Re: rate constants

Yes! Rate constants are always positive because concentrations cannot be negative values.

Jasmine W 1K
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### Re: rate constants

Rate constants are always positive because concentrations cannot be negative.

Leila_4G
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### Re: rate constants

In what case would we ever get a negative rate constant?

Leila_4G
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Joined: Sat Sep 14, 2019 12:17 am

### Re: rate constants

Also, will we ever get a graph with a curve of lnA/t even if we have the correct order reaction? I thought I saw an example like that in the book but I was confused.

kristi le 2F
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Joined: Thu Jul 11, 2019 12:15 am

### Re: rate constants

Rate constants will be positive, but you can still get a graph with a negative slope, such as in 1st order reactions where the slope is -k.

Nare Nazaryan 1F
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### Re: rate constants

Since rate constants depend on concentration (which is positive), they are always positive.

Maika Ngoie 1B
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### Re: rate constants

Because concentration can never be a negative value, it is always positive.

EMurphy_2L
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### Re: rate constants

Leila_4G wrote:In what case would we ever get a negative rate constant?

for 0 or 1 order reactions in which the slope is negative!

Samuel Tzeng 1B
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Joined: Sat Aug 24, 2019 12:15 am

### Re: rate constants

the rate constant is always positive

Celine 1F
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Joined: Fri Aug 02, 2019 12:16 am

### Re: rate constants

Rate constants should always be positive

Posts: 50
Joined: Tue Nov 05, 2019 12:18 am

### Re: rate constants

Yes, they're always positive!

Anthony Hatashita 4H
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Joined: Wed Sep 18, 2019 12:21 am

### Re: rate constants

Rate constants are always positive because they are based off time and concentrations which are always positive.