*And this is an ultra fancy word that often makes people think it's difficult. There's not just one type of stoichiometry problem, but they're all along the lines of, if I give you x grams of this how many grams of aluminum do I need to make this reaction happen?*But it's really just the study or the calculation of the relationships between the different molecules in a reaction. Or if I give you y grams of this molecule and z grams of this molecule which one's going to run out first? And we'll actually do those exact two types of problems in this video.

So if we're given an unbalanced one, we know how to get to the balanced point. Because for every mole of the iron three oxide, we have two moles of aluminum. So that's equal to, 85 divided by 160 equals 0.53125. So everything we've done so far in this green and light blue, we figured out how many moles 85 grams of iron three oxide is. If we have 0.53 moles, you multiply that by 2, and you have 1.06 moles of aluminum.

And we're just looking at the coefficients, we're just looking at the numbers. All right, so we just have to figure out how many grams is a mole of aluminum and then multiply that times 1.06 and we're done.

The constituent parts of a chemical equation are never destroyed or lost: the yield of a reaction must exactly correspond to the original reagents.

This fact holds not just for the type of elements in the yield, but also the number.

One molecule of iron three oxide combines with two molecule of aluminum to make this reaction happen. Let's say we're dealing with the version of iron, the isotope of iron, that has 30 neutrons. So aluminum, or aluminium as some of our friends across the pond might say. Aluminium has the atomic weight or the weighted average is 26.98. Or 6.02 times 10 to 23 aluminium atoms is going to be 27 grams. So we need 28.62 grams of aluminium, I won't write the whole thing there, in order to essentially use up our 85 grams of the iron three oxide.

So lets first figure out how many moles 85 grams are. So let me go down and figure out the atomic masses of iron and oxygen. But let's just say that the aluminium that we're dealing with has a mass of 27 atomic mass units. So if we need 1.06 moles, how many is that going to be? And if we had more than 28.62 grams of aluminium, then they'll be left over after this reaction happens.Given our unbalanced equation: describe how many atoms of an element are in a molecule.) This unbalanced reaction can't possibly represent a real reaction because it describes a reaction in which one Fe atom magically becomes two Fe atoms. The process of balancing an equation is basically trial and error. You will likely start to balance equations almost automatically in your mind.Therefore, we must balance the equation by placing coefficients before the various molecules and atoms to ensure that the number of atoms on the left side of the arrow corresponds exactly to the number of elements on the right. The process of converting given units into moles involves conversion factors.This lesson will teach you how to relate the mole ratio to the amounts of substances in grams.For either reactants or products, you will learn how to determine mass when given moles, moles when given mass and mass when given mass.This is the actual definition that Wikipedia gives, stoichiometry is the calculation of quantitative, or measurable, relationships of the reactants and the products. So let's say that we were given 85 grams of the iron three oxide.And you're going to see in chemistry, sometimes people use the word reagents. Aluminum, on the left hand side we only have one aluminum atom. So my question to you is how many grams of aluminum do we need?But for our purposes a reagent and reactant is the same thing. But I think it's good practice to actually balance the equations ourselves. We have two iron atoms here in this iron three oxide. So what we need to do is figure out how many moles of this molecule there are in 85 grams. So one mole or 6.02 times 10 to the 23 molecules of iron oxide is going to have a mass of 160 grams. So if we have 0.53 moles of the iron molecule, iron three oxide, then we're going to need twice as many aluminum. For every molecule of this, we need two molecules of that.So it's a relationship between the reactants and the products in a balanced chemical equation. Just so we get practice balancing equations, I'm always going to start with unbalanced equations. How many iron atoms do we have on the right hand side? And then we need to have twice as many moles of aluminum. This mass is going to be 2 times 56 plus 3 times 16. But this isn't a math video, so I'll get the calculator out. So in our reaction we said we're starting off with 85 grams of iron oxide. Well 85 grams of iron three oxide is equal to 85 over 160 moles. So we're going to need 1.06 moles of aluminum. So for every mole of this, we need two moles of this.You can test out of the first two years of college and save thousands off your degree.Anyone can earn credit-by-exam regardless of age or education level.

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