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Limiting Reactant

Posted: Mon Oct 01, 2018 4:20 pm
by AlyssaBei_1F
On the limiting reactant video, the example is calcium carbonate reacts with water to form calcium hydroxide and ethyne. I understand up to calculating the moles of CaC2 and H2O, but am confused why we have to multiply 1.56 (moles of CaC2) by 2. Can someone help me with this?

Re: Limiting Reactant

Posted: Mon Oct 01, 2018 4:32 pm
by Hai-Lin Yeh 1J
The reason he says that you multiply 1.56 (moles of CaC2) by 2 is because in the balanced chemical equation, it says that 1 mole of CaC2 reacts with 2 mole of H2O.

1CaC2 (s) + 2H2O (l) -> Ca(OH)2 (aq) + C2H2 (g)

By looking at the stoichiometric coefficients in the chemical equation, we see that for every 1 CaC2, 2 H2O is required. Thus, since you currently have 1.56 moles of CaC2, that means you need 3.12 mol of H2O.

Re: Limiting Reactant

Posted: Mon Oct 01, 2018 9:13 pm
by Parth Mungra
In the reaction it takes 2 moles of water for every 1 mols of calcium carbide. The problem was given with information that will let you get 1.56 mol of CaC2 and 5.55 mol of water. Because of the 1:2 ratio, we have to check to see how many mols of water molecules will be used with the given amount of CaC2. So, multiply 1.56 with the 2 mol H2O to get 3.12 mol H2O. With the information that you calculated earlier, we can find that we do have a sufficient amount of water molecules for this reaction to take place, but because we only have 1.56 mol of calcium carbide, we can only us 3.12 mol of water, making calcium carbide the limiting reactant.

Hope this helps