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GOB Chemistry

Learn the toughest concepts covered in your GOB - General, Organic, and Biological Chemistry class with step-by-step video tutorials and practice problems.

Stoichiometry deals with the numerical relationship between compounds in a balanced chemical equation.

Stoichiometry

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Stoichiometry

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when it comes to chemical equations, it becomes important to first balance your chemical equation because this will later on lead us to our understanding of story geometry. Now, story geometry deals with the numerical relationship between compounds in a balanced chemical equation. It allows us to determine the amount of products from reactant and vice versa. For example, here we have our chemical equation. That's balance we have to Hydrogen gas is reacting with one oxygen gas to produce to water molecules as gas. They're giving us 12.3 g of H two, and they're asking us to determine the grams of H 20 H. 20 gas produced. This is what store geometry is. They're giving us a balanced chemical equation. They're giving us information on one of the compounds within this balanced equation and asking us to find another compound within that same balanced equation. Now that we know what's dark geometry is, how exactly do we do it? Well, if you click on the next video, we'll take a look at the procedures that you'll need to employ in order to do any type of stoke geometric calculation.

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Stoichiometry

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So as we said, we're given 12.3 g of H two. And as to find how many grams of H 20 would form the way we're able to do this is through stock geometry and to find how many grams would use these Tokyo metric chart. Now, the chart uses the given quantity of a compound to determine the unknown quantity of another compound. The way it works is we're starting here on the left side and on the left side. The information they give to us is called the Given Information. Now this information that's given to us can be presented as grams and if it's presented his grams, then we can just do a conversion to get two moles so we can go from grams of given two moles of given now. Besides giving it to us in grams, it could be given to us in ions, Adams formal units no or molecules of given. Again. We're heading towards moles of given, so our basic movement is going from the left side of the chart. Towards the right side of the chart toe are unknown information. Now that we have our moles of given, we'd have to basically take a jump, a leap of faith from an area where we know information because it's given to us tow a area where we know nothing at all. So it's unknown to us and this jumper leap of faith that we're going to take. We call it the jump. To be able to do this jump, you have to do a mole to mole comparison and in a multiple comparison, use the coefficients in the balanced equation. That's why it's incredibly important. You first have a balanced equation before you even attempt to do so. A geometry once we've gone from moles of given, two moles of unknown And then we can either stop there if they want us to find the answer in moles or continue onward to ions, Adams formula units or molecules of unknown or toe grams of unknown. In this case, from the example that we have up above of our equation, we would say that this is the grams given to us, so this would be our grams off given and we'd have to basically take the trip of grams of given two moles of Given. Two moles of our unknown are unknown is what we're looking for, which would be water, and then we'd have to stop here at grams of unknown. That's the path we have to take. We utilize this Tokyo metric chart to help us answer any type of stoking metric question. Now that we've seen this chart, move on to our example question and let's put it to work put into practice in terms of this story geometric chart.

Utilize the stoichiometric chart to do all your stoichiometric calculations.

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Stoichiometry Example 1

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here in this example question. It says how many grams of h 20 are produced when 12.3 g of H two reacts. All right, so we know that they're giving us information on one compound in a balanced equation and asking for information on another. We know that is the definition of stock geometry. So we're gonna have to utilize this Don't geometric chart in some way to solve this problem. Now, if we follow the steps, it's a step one map out the portion of the Stoke geometric chart you will use from the question they're giving us 12.3 g of H two. Since that's a value they're giving to you that represents our grams of Given. So we're gonna start at grams of Given, which is just grams of h two, and we're gonna convert those grants into moles of Given. So moles of H two Now in the same question, they're asking us to find the grams of H 20 Since we don't know information on H two on, they're asking us to find it. This represents our grams off unknown. Okay, so that tells me I have to go for moles of Given and find a way to get 2 g of unknown. Now, at this point to go from moles of Given, I have to go to moles of unknown, and that is where it's required to do the job. So we're gonna go from moles of Given two moles of unknown. And then finally, we go from moles of unknown to grams of unknown. This is the path that we're gonna take to answer this question. So let's go to Step two, it says Convert the given quantity into moles of Given. And if a compound is said to be in excess, then just ignore it In this question, they don't say anything as being in excess. So we don't have to worry about this, uh, next line. Understand to later on, we'll come into situations where we're told something is in excess, and in that case, we just simply ignored. All right, so we're gonna take our given quantity, which is 12.3 g h two, and we're gonna convert it into moles of given grams of H to go on the bottom and one mole of H two goes on top H two has in it to hydrogen, and according to the periodic table, each one weighs 1.8 g. So that's 2.16 g grams. Here, cancel out and I'll have moles of H two, which comes out to 6.1012 Moles of H two. So I've just gone from grams of h two. So malls of H two. At this point, we have to do the jump. So going to stop three. It says to do a mole to mole conversion in order to convert moles of given into moles of unknown. So we take that 6. moles of H two to get rid of moles of H two. I put them on the bottom What am I looking for? I'm looking for my unknown My unknown is water So I need to find moles off h now remember to go from moles of given two moles of unknown That's called the jump and we do a multiple comparison The equation says that for every two moles of H two, I have two moles of H 20 So for every two moles of H two I have two moles of H 20 So here moles of H to cancel out. And now I have moles of H 20 So that's 6.1012 moles of H now finally, if necessary, convert the moles of unknown into the final desired units. Sometimes they may ask us to just find the moles of are unknown And in that case we'd stop for this particular question Though they're not asking us to find moles of water, they're asking us to find grams of water so an additional step is required. So 6.10 12 moles of H two Oh got to get rid of most of h two Also one mole of age tool on the bottom How many grams of h 12 do we have on top H 20 was composed of two hydrogen and one oxygen Hydrogen according to periodic table is 1.8 g. Oxygen is 16 g this is 2016 g and this is 16 g So the complete mass of H 20 is 18 016 g So we plugged that here Moles of water cancel out and now I'm finally gonna have grams of water. So here we're going to multiply those out. So that's 1199 g of H Now, technically, within this question, 12.3 has three significant figures. So technically, we should write this in three significant figures as well. So in scientific notation that will come out toe 1.10 times 10 to the 2 g of H 20 So this would be our final answer for this Tokyo metric question. So remember if we were given the amount of ah compound within a balanced equation and asked to find another, we're dealing with stoke geometry, which means you have to utilize this Tokyo metric chart in order to find your final answer.

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Problem

The oxidation of chromium solid is represented by the following equation:

How many moles of chromium (III) oxide are produced when 34.69 g Cr reacts with excess oxygen gas?

A

0.334 mol

B

1.33 mol

C

0.749 mol

D

3.00 mol

E

0.667 mol

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Problem

The reaction of potassium chlorate and sucrose is given below:

If 2.33 x 10^{-7} formula units of potassium chlorate are reacted, how many grams of carbon dioxide will be produced?

A

3.94x10^{-16} g CO_{2}

B

8.23x10^{-23} g CO_{2}

C

2.72x10^{-21} g CO_{2}

D

7.81x10^{-23} g CO_{2}

E

2.55x10^{-29} g CO_{2}

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Problem

If the density of ethanol, CH_{3}CH_{2}OH, is 0.789 g/mL, how many milliliters of ethanol are needed to produce 4.8 g of H_{2}O in the following reaction?