Mass Always Equal?

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Alexandra Watts 3L
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Joined: Wed Sep 21, 2016 2:56 pm

Mass Always Equal?

Postby Alexandra Watts 3L » Sun Sep 25, 2016 11:44 am

If the mass of a chemical reaction never changes from the initial reactants to the final product, in what aspect does the limiting reactant affect the reaction?

Kathy Vu 3L
Posts: 24
Joined: Fri Jul 15, 2016 3:00 am

Re: Mass Always Equal?

Postby Kathy Vu 3L » Sun Sep 25, 2016 12:17 pm

The limiting reactant limits the amount of product that can be formed and is completely consumed, therefore the other reactant (excess reactant) will remain when the reaction stops.

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Joined: Sat Jul 09, 2016 3:00 am

Re: Mass Always Equal?

Postby Preet_Bains_1D » Sun Sep 25, 2016 12:42 pm

Since there is a specific ratio between, for example, two reactants for the reaction, only a certain amount of Reactant A will be used in respect to Reactant B so whichever one "runs out" first is limiting the reaction because no more of it is available and the one remaining is in excess. I think you're confusing the conservation of mass principle in this instance since you're thinking that the excess reactant that remain is part of the conservation of mass but you're not supposed to include it when you compare the mass of reactants and products, you only include the mass of the reactants that actually reacted. Hope that helps.

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Re: Mass Always Equal?

Postby em_farag » Sun Oct 02, 2016 12:17 pm

If A reacts with B and B is the limiting reactant, B will be completely used up in the reaction while there is still some left of A. The conservation of mass applies to whatever portion of A and B react, but the mass left over from A (the reactant in excess) can also be included in the end mass. You can disregard the unused mass of A (the reactant in excess), as Preet_Bains stated, but really you can include A's unreacted mass because it will be unchanged by the reaction.

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