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Author Topic: limiting and excess reactants  (Read 5926 times)

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croatian

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limiting and excess reactants
« on: May 21, 2007, 06:04:07 AM »

Which of the following is NOT true about limiting and excess reagents?

a.)The amount of product obtained is determined by the limiting reagent.
b.)Some of the excess reagent is left over after the reaction is complete.
c.)A balanced equation is necessary to determine which reactant is the limiting reagent.
d.)The reactant that has the smallest given mass is the limiting reagent



I know that A is true and that B is true for sure. I am not sure about C. To me it seems that I always balance an equation, but maybe that is unneccesary work. My guess though is that because of molar mass, D is not true.

Am i correct?
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Borek

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Re: limiting and excess reactants
« Reply #1 on: May 21, 2007, 06:40:41 AM »

a, b - true, d - false. c - true seems to be safe answer, but it is - in general - wrong. In some cases situation is obvious even without knowledge about the reaction - if you have mg of hydrocarbon and ton of oxygen, and you plan to burn hydrocarbon, it is obvious what is a limiting reagent. Still, your teacher may not want to accept such explanation.
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enahs

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Re: limiting and excess reactants
« Reply #2 on: May 21, 2007, 07:19:14 AM »

I agree with Borek, about it being a safe answer and you can reasonably defend it to your teacher.

But I personally would say it is clearly not true.

I do not have to be a chemist, or even ever heard the word chemistry before, and can mix two chemicals and cause a reaction, with out having any clue what the chemicals are or what the reaction is (and thus no equation, balanced or not) and see in the end I still have excess of compound A left.
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Borek

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Re: limiting and excess reactants
« Reply #3 on: May 21, 2007, 07:25:56 AM »

can mix two chemicals and cause a reaction, with out having any clue what the chemicals are or what the reaction is (and thus no equation, balanced or not) and see in the end I still have excess of compound A left.

Let's call it "experimental determination" (courtesy of Bill Bare ;) )
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