## Excess reactants

McKenna_4A
Posts: 95
Joined: Sat Aug 24, 2019 12:18 am

### Excess reactants

Once I've found a limiting reactant, how do I calculate how much of the reactant in excess remains?

Matthew Chan 1B
Posts: 91
Joined: Sat Sep 07, 2019 12:16 am

### Re: Excess reactants

You take the amount of reactant which is responsible for limiting the amount of product, and you have to calculate the number of moles of reactant, then multiply that by the ratio of moles in the chemical equation of limiting reactant to the excess reactant. (you're solving for the amount of the excess reactant. this value tells you how much was used in the reaction.) Then, calculate the mass of the excess reactant. Next, subtract that value from the amount of excess reactant that you were given in the problem. I'm pretty sure that this explanation made no sense, so I've attached an image of an example that will hopefully help a little bit.

https://photos.app.goo.gl/7gwVnhTpRANBthxG8
Attachments

LNgo 1G
Posts: 83
Joined: Sat Aug 24, 2019 12:16 am

### Re: Excess reactants

You can use stoichiometry to calculate the amount of the excess reactant that is used in the reaction with the amount of the limiting reactant that you have. Then subtract the value of the excess reactant used in the reaction from the amount given.

Amy Pham 1D
Posts: 88
Joined: Fri Aug 09, 2019 12:15 am

### Re: Excess reactants

mass of limiting reactant/molar mass of limiting reactant = mols of limiting reactant

given mols of limiting reactant/given mols of excess reactant = calculated mols of limiting reactant/x, which is the amount of excess reactant used (in mols)

(mols of excess reactant used) x (molar mass of excess reactant) = mass of excess reactant used

given mass of excess reactant - mass of excess reactant used = mass of excess reactant remaining

Hope this helps!