Homework Question

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Doreen Liu 4D
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Joined: Wed Sep 11, 2019 12:17 am

Homework Question

Postby Doreen Liu 4D » Thu Oct 03, 2019 8:21 am

Can someone help me with this limiting reactant problem? "Find limiting reagent if 21.4g NH3 is reacted with 42.5g of O2." How do I find the limiting reagent if the ratio is not 1:2?

Victoria Zheng--2F
Posts: 103
Joined: Fri Aug 09, 2019 12:17 am

Re: Homework Question

Postby Victoria Zheng--2F » Thu Oct 03, 2019 8:39 am

To find the limiting reagent for this question, you would first write a balanced equation, and then convert the reactants from grams to moles by using their molar mass, and then you compare the molar ratio between the two reactants. If they have a 1:1 ratio, then that means the number of moles for both reactants should be the same, so the reactant with the greater number of moles would be the excess reactant, and the reactant with the fewer number of moles would be the limiting reagent. I hope this answers your question.

Naji Sarsam 1F
Posts: 104
Joined: Sat Aug 17, 2019 12:18 am

Re: Homework Question

Postby Naji Sarsam 1F » Thu Oct 03, 2019 8:41 am

When doing a limiting reactant problem, you should first convert both masses of reactants to the respective moles you have of each reactant. Then, referring back to the chemical reaction--which sould be balanced--you should look at the mole to mole ratio of the first reactant to the second. Next, pick one of either reactant and use stoichiometry to calculate how many moles of the second reactant you would need. If this number is greater than the number of moles you have for the second reactant, then the second reactant is the limiting reactant. If the calculated number of moles needed is less than the number of moles you have for the second reactant, then the first reactant is the limiting reactant.

dtolentino1E
Posts: 101
Joined: Thu Jul 11, 2019 12:17 am

Re: Homework Question

Postby dtolentino1E » Thu Oct 03, 2019 8:45 am

hi there! if you balance the equation, i believe it actually comes out to 4 molecules of NH3 for 5 molecules of O2.
4NH3(g) + 5O2(g) ---> 4NO(g) + 6H2O(g)
because of this, when you calculate moles of reactants, you must take into account the molar ratio of these molecules before deciding the limiting reactant.


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