Solving Limiting Reactant Problems

The other reactants are partially consumed where the remaining amount is considered "in excess".

This example problem demonstrates a method to determine the limiting reactant of a chemical reaction.

Once we've determined how much of each product can be formed, it's sometimes handy to figure out how much of the excess reactant is left over.

This task can be accomplished by using the following formula: In our limiting reactant example for the formation of water, we found that we can form 2.75 moles of water by combining part of 1.75 moles of oxygen with 2.75 moles of hydrogen.

Now that you're a pro at simple stoichiometry problems, let's try a more complex one.

Using the recipe for ice water (1 glass of water 4 ice cubes = 1 glass of ice water), determine how much ice water we can make if we have 10 glasses of water and 20 ice cubes.The excess reactant remains because there is nothing with which it can react.No matter how many tires there are, if there are only 8 car bodies, then only 8 cars can be made. That's NH3 and it's a gas, that's why the g is in parentheses. That's also a gas, it's also called nitric oxide, not to be confused with nitrous oxide. If we multiply this times one and a half, 1.5, now we have three hydrogens on this side. How many oxygens do we have on the right-hand side? And then making sure that you understand the ratios.And we combine that with some oxygen, molecular oxygen, it's also a gas. I'll write nitrous oxide, it's N2O, this is laughing gas. 1.5 times 2, we have three hydrogens on the right-hand side. We have one oxygen here, and we have one oxygen in this molecule, but we have one and a half of the whole molecule. You understand this is a 4:5 ratio, there's always going to be less ammonia than oxygen.Likewise with chemistry, if there is only a certain amount of one reactant available for a reaction, the reaction must stop when that reactant is consumed whether or not the other reactant has been used up.A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen.Which is the limiting reactant and how much excess reactant remains after the reaction has stopped?First, we need to create a balanced equation for the reaction: Next we can use stoichiometry to calculate how much product is produced by each reactant.Hopefully, you didn't have too much trouble figuring out that we can make only five glasses of ice water.Let's go through this calculation carefully to see what we did (it'll be clear why we need to do this in a second).


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