Finding Excess Reactant  [ENDORSED]

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Fiona Grant 1I
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Joined: Fri Apr 06, 2018 11:03 am

Finding Excess Reactant

Postby Fiona Grant 1I » Sun Apr 15, 2018 2:55 pm

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?

Natalie Noble 1G
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Joined: Thu Feb 01, 2018 3:02 am
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Re: Finding Excess Reactant  [ENDORSED]

Postby Natalie Noble 1G » Sun Apr 15, 2018 2:57 pm

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

Ziana Bhanji 1E
Posts: 30
Joined: Fri Apr 06, 2018 11:01 am

Re: Finding Excess Reactant

Postby Ziana Bhanji 1E » Sun Apr 15, 2018 3:00 pm

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

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