Chemistry  Equations
posted by Theodore .
I am a student in the ninth grade and I need help with the following problems because I do not understand how to do them. I appreciate your help and thanks once again.
7. in 2CO(grams) + O2(grams) => 2CO2(grams), what is the ratio of moles of oxygen used to moles of CO2?
9. when iron rusts in air, iron(III) oxide is produced. how many moles react with 2.4 iron in the rusting reaction? 4Fe(s) + 3O2(g) => 2Fe2O3(s)
22. iron (III) oxide is formed when iron combines with oxygen in the air. how many grams of Fe2O3 are formed when 16.7g of Fe reacts completely with oxygen? 4Fe(s) + 3O2(grams) => 2Fe2O3(s)
23. aluminum reacts with sulfuric acid to produce aluminum sulfate and hydrogen gas. how many grams of aluminum sulfate would be formed if 250g H2SO4 reacted with aluminum?
24. how many liters of chlorine gas can be produced when .98L of HCl react with excess O at STP? 4HCl(g) + O2(g) => 2Cl(g) + 2H2O(g)
27. which would be the limiting reagent in the reaction: 2H2(g) + O2(g) => 2H2O(g)
a. 50 molecules of H2
b. 50 molecules of O2
31. at STP, how many liters of oxygen are required to react completely with 3.6 liters of hydrogen to form water? 2H(g)+ O2(g) => 2H2O(g)
37. if 8.6L of H2 reacted with 4.3L of O2 at STP, what is the volume of gaseous water collected (assuming none of it condenses)? 2H2(g) + O2(g) => 2H2O(g)
38. how many liters of O2 are needed to react completely with 45L of H2S at STP? 2H2S(g) + 3O2(g) => 2SO2(g) + 2H2O(g)
39. for the reaction 2Na(s) + Cl2(g) => 2NaCl(s), how many grams of NaCl could be produced from 103g of Na and 13L of Cl2 (at STP)?
46. how many grams of CO are needed to react with an excess of Fe2O3 to produce 209.7gFe? Fe2O3(s) + 3CO(g) => 3CO2(g) + 2Fe(s)

You will get more help if you post one problem per post.
Next, I will show you how to do the FIRST one and you can use that method to work all of them. If you have trouble with any of the others, please post that problem, show your work, and explain in detail what you don't understand. 
Sorry about that. I pushed the submit button before I finished the last post. Here are the first TWO.
7. in 2CO(grams) + O2(grams) => 2CO2(grams), what is the ratio of moles of oxygen used to moles of CO2?
Look at the equation. The coefficients tell you how many mols react with how many mols. Ratio means mols one atom divided by mols of the other atom. mols oxygen used is 1 (the coefficient of O2 is 1 in the balanced equation. The # mols CO2 formed is 2 (again from the equation). Therefore, the ratio of O2 to CO2 is 1/2.
I will post #9 next. 
9. when iron rusts in air, iron(III) oxide is produced. how many moles react with 2.4 iron in the rusting reaction? 4Fe(s) + 3O2(g) => 2Fe2O3(s)
You have omitted part of the problem. I assume you mean, "How many mols of oxygen react with 2.4 g iron in the rusting reaction?"
1. Write the balanced equation.
4Fe(s) + 3O2(g) ==> 2Fe2O3(s)
2. Convert what you are given to mols remembering that mols = grams/molar mass. mols Fe = grams/atomic mass Fe = 2.4/55.8 = 0.0624 mols Fe. Check my arithmetic.
3. Look at the equation and convert mols Fe to mols oxygen using the coefficients in the balanced equation.
mols oxygen = mols Fe x (3 mols O2/4 mols Fe) = 0.0468 mols O2. (Note how the units we DON'T want cancel and the unit we want to keepin this case we want mols Fe to cancel and we want to keep mols O2). This is the answer to the problem.
4. That answers this question BUT if you needed grams O2 (and more problems ask for grams than not), you would take this number of mols O2 and convert to grams. grams = mols x molar mass = 0.0468 x 32 = ??

you can dane in you try come on you can do it!! keep trying!

1.2?

HOW MANY GRAMS OF CO ARE NEEDED TO REACT WITH AN EXCESS OF Fe2O3 TO PRODUCE 209.7 GRAMS Fe ?

27. which would be the limiting reagent in the reaction: 2H2(g) + O2(g) => 2H2O(g)
a. 50 molecules of H2
b. 50 molecules of O2
What is the answer to this? 
a and b. they can both limit the reaction
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