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Finding Excess Reactant

Posted: Sun Apr 15, 2018 2:55 pm
by Fiona Grant 1I
I understand how to find the amount of product formed from a limiting reactant. But how exactly do you calculate the mass of the excess reactant that is leftover once this reaction takes place?

Re: Finding Excess Reactant  [ENDORSED]

Posted: Sun Apr 15, 2018 2:57 pm
by Natalie Noble 1G
First you find which is the limiting and excess reactant

Take the initial mass of limiting reactant (most likely given to you in the problem) and find how much ER is needed to react all of the LR:

(mass of LR) *(1 mol LR/molar mass LR) * ( __mol ER/ __mol LR) * (molar mass ER/1 mol ER) = the mass of ER needed to react with all the LR

( __mol ER/ __mol LR) is the mol to mol ratio that you get from the balanced equation of the reaction

The problem tells you the initial mass of the ER

Initial mass ER - mass of ER you found above = left over excess reactant

Re: Finding Excess Reactant

Posted: Sun Apr 15, 2018 3:00 pm
by Ziana Bhanji 1E
Once you identify your limiting reactant, you calculate how much of the other reactant it must have reacted with and subtract from the original amount.

Here's a website that might help. It has a video explanation too: ... -how-do-yo