more rate

[chiddler]

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Which does not always affect rate?

Adding solvent to reaction
or
Adding reagent

Adding solvent is the equivalent of reducing concentration "including the reactants in the rate limiting step". 0 order reactions do not depend on concentration.

Adding reagent is the same as increasing concentration. 0 order reactions do not depend on concentration!

BR says the latter is correct.

 

[MedPR]

Which does not always affect rate?

Adding solvent to reaction
or
Adding reagent

Adding solvent is the equivalent of reducing concentration "including the reactants in the rate limiting step". 0 order reactions do not depend on concentration.

Adding reagent is the same as increasing concentration. 0 order reactions do not depend on concentration!

BR says the latter is correct.

Solvents can also change the conformation of reactants, affect bonding, etc.

 

[chiddler]

Solvents can also change the conformation of reactants, affect bonding, etc.

i assumed that they added the same solvent that the reaction was already in.

So if it is the same solvent then i'm correct; it will not affect rate. Yes?

 

[MedPR]

i assumed that they added the same solvent that the reaction was already in.

So if it is the same solvent then i'm correct; it will not affect rate. Yes?

I'm not sure. I understand what you are saying about 0 order rate being independent of the reactant concentration, but if you were to add more of the same solvent, you might increase solvation or the rate of some other side-reaction that could ultimately affect the rate of the original 0 order reaction..

I'm not sure though. Hopefully BR teach will pop in.

 

[phaloz]

Well we know for sure the rate is not always affected by concentration of reagents. We also know that solvent properties can effect the rate for all orders of reaction. By this information alone we can pick the correct answer. The question is, does adding any type of solvent affect reaction rate ? Hopefully someone knows.

 

[typicalindian]

I think It's adding reagent. Depending on the order of reaction certain reagents may or may not affect rate and if you add those then rate won't change. However, adding any solvent in addition to what you have will lower the concentration of every reagent in your container so the rate can only slow down.

Edit: like A + B -> C if the rate is k[A] then by adding B you won't change the rate. But if you added solvent you'd decrease concentrations of A and B so you would lower the rate.

 

[MedPR]

Well we know for sure the rate is not always affected by concentration of reagents. We also know that solvent properties can effect the rate for all orders of reaction. By this information alone we can pick the correct answer. The question is, does adding any type of solvent affect reaction rate ? Hopefully someone knows.

Your reasoning doesn't really work to answer this problem. The problem doesn't specify if you are adding more of the same reagent or adding a different reagent. If you add a different reagent you can certainly change the rate of a 0-order reaction, but adding the SAME reagent won't change it.

 

[chiddler]

The answer only says what I quoted in the OP. It does not mention anything about changing properties of solvent.

To me this is a strong indication that it's just more of the same solvent that is added.

 

[MedPR]

The answer only says what I quoted in the OP. It does not mention anything about changing properties of solvent.

To me this is a strong indication that it's just more of the same solvent that is added.

I can't think of a situation where adding more of the same solvent would affect the rate of a 0-order reaction, but I can say with certainty that adding more of the same reagent would not affect the rate of a 0-order reaction. Based on that alone, I would have picked answer B (the second one you have in the OP).

 

[MrNeuro]

zero order rxns are typical of enzyme or catalyst based rxns at high concentrations they act as zero order however at lower concentrations they behave as first order reactions

increasing the solvent will decrease the concentration of reactant and will now make the reaction dependent upon availability of reactant and no longer dependent on enzyme availability

it may also be worth noting that some books actually do include the enzyme in the rate value i dont know why TBR doesn't do it maybe its only a bio thing i dunno.....but that should help answer your question

if that doesnt then you also can use this

for zero order reactions

rate = k
we know that k = Ae^(-Eact/RT)
we also know that for a 0 order rxn

t1/2 = [A]o / 2k

k= [A]o/2t1/2 (not 100% sure if you can do this rearrangment but i dont see why not)

based on this decreasing [A]o decreases k which decreases the rate

other explanations here are probably also valid
if the solvent is diff they it can affect transition state stability and effectively increase or decrease Ea

however what typicalindian said is the way to go
adding a reactant will not always change your rate

 

[chiddler]

You're suggesting that in a 0 order reaction, rate of reaction depends on concentration. That's definitely incorrect.

If that were the case, we'd see the reaction slow down as it approaches completion which is not observed.

Your first point may be valid, but that's too specific a detail to apply to this question, don't you agree?

 

[411309]

Adding reactants won't always affect the rate I agree with that. If the reactant is zero order with respect to the rate law then its concentration is independent of the rate, so adding more of it wont do anything to the actual rate of the reaction.

Adding more solvent will, because it will essentially dilute the concentration of all the reactants.

 

[chiddler]

Adding reactants won't always affect the rate I agree with that. If the reactant is zero order with respect to the rate law then its concentration is independent of the rate, so adding more of it wont do anything to the actual rate of the reaction.

Adding more solvent will, because it will essentially dilute the concentration of all the reactants.

but the reactants don't depend on concentration if it's 0 order, no?

 

[411309]

correct. I think I see what you are trying to say. Are you trying to say what if all the reactants were zero order, then theoretically adding more solvent would do nothing? Because I don't think that's possible. The ocverall rate could first order, and we could say first order with respect to reactant A and zero order with respect to reactant B. And if we added more B wed do nothing to the actual rate of the reaction. But if we added more solvent wed decrease A which would affect the rate.

 

[chiddler]

correct. I think I see what you are trying to say. Are you trying to say what if all the reactants were zero order, then theoretically adding more solvent would do nothing? Because I don't think that's possible. The ocverall rate could first order, and we could say first order with respect to reactant A and zero order with respect to reactant B. And if we added more B wed do nothing to the actual rate of the reaction. But if we added more solvent wed decrease A which would affect the rate.

Oh that's an interesting thought. So it's impossible for an entire reaction to be 0 order. This makes logical sense because imagine a solution the size of the ocean with 2 molecules of reagent. Zero order says they should react.

So zero order should only be relevant with respect to certain reagents OR under special circumstances such as enzyme + saturated reagent, causing no increase in rate with added reagent.

 

[411309]

Oh that's an interesting thought. So it's impossible for an entire reaction to be 0 order. This makes logical sense because imagine a solution the size of the ocean with 2 molecules of reagent. Zero order says they should react.

So zero order should only be relevant with respect to certain reagents OR under special circumstances such as enzyme + saturated reagent, causing no increase in rate with added reagent.

I would think an overall zero order reaction would not be possible because youd have rate=..... lol. Since zero order reagents dont get listed in the rate law.

but i am also crazy tired, i could have missed something you wrote. rawr.

 

[MrNeuro]

You're suggesting that in a 0 order reaction, rate of reaction depends on concentration. That's definitely incorrect.

If that were the case, we'd see the reaction slow down as it approaches completion which is not observed.

Your first point may be valid, but that's too specific a detail to apply to this question, don't you agree?

i think it makes sense because 0 orders to a certain extent are dependent upon concentration its just that the concentration is usually super high so an decrease really doesn't show a change in rate until you pass a critical point where then it exhibits first-order

zero orders are weird b/c at a certain critical point they are no longer zeroth order or else the rxn would just keep going....which is sort of impossible b/c your bound to run out of reactants

so you technically only see zero order kinetics for a certain period of time (until you hit a critical point).

this figure may help

the black dashed line is when you've hit that critical point where it now is dependent upon reactant concentration

that help?

 

[gettheleadout]

I would think an overall zero order reaction would not be possible because youd have rate=..... lol. Since zero order reagents dont get listed in the rate law.

but i am also crazy tired, i could have missed something you wrote. rawr.

For zero order reactions rate = k

 

[chiddler]

okie i'm satisfied with the answer.

thanks for the very generous help, everyone.

 

[411309]

For zero order reactions rate = k

Yeah I forgot to put the K. Don't be hatin I was tires lol