1.00 L of methyl alchohol vapor, CH3OH with 20.0 L of oxygen at STP. 2 CH3OH + 3 O2 ---> 2 CO2 + 4 H2O How many liters of water will be formed in the reaction. of H2O? Which reactant was limiting? Which reactant was excess?


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John McCann Profile
John McCann answered

The other two problems that I think you submitted ( above this one ) are simple stoichiometry and you should be able to solve them yourself. This one is different.

2CH3OH +  3O2 --->  2CO2 +  4H2O

(place molar coefficients directly before species)

We will now use the ideal gas equation to get moles of methyl alcohol vapor and oxygen.  PV = nRT

(1 atm)(1.00 L CH3OH) = n(0.08206 L*atm/mol*K)(273.15 K)

n = 1.00/22.415

= 0.0446 moles CH3OH


(1 atm)(20.0 L O2) = n(0.08206 L*atm/mol*K)(273.15 K)

n = 20/22.415

= 0.8923 moles O2

------ Now, find limiting reactant. I suspect CH3OH limits.

0.0446 moles CH3OH (3 mol O2/2 mol CH3OH)

= 0.0669 moles

------You do not have that many moles CH3OH, so CH3OH limits the reaction and will drive the reaction. ( Try O2 and see that it is in excess )

------Now, drive the reaction to get moles water.

0.0446 moles CH3OH (4 mol H2O/2 CH3OH)

= 0.0892 moles water

------ Once more with the ideal gas equation.

(1 atm)( L) = (0.0892 moles H2O)(0.08206 L*atm/mol*K)(273.15 K)

L = 1.999/1

= 2.00 Liters water produced ( final answer )

======( the limiting reactant and the excessive reactant is noted above )

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John McCann
John McCann commented
What was your major? Do you work along those lines now?
HappyTo BeHereTo
HappyTo BeHereTo commented
I majored in Elementary Education. That's why I answer homework questions with an eye toward the student's future ability to solve problems independently. All those steps and visualizations are time consuming, but hopefully worthwhile. :)

I chose a BS instead of the more common BA, so I could take more math. But unfortunately, I was only able to reach Calculus II. The diversity of El Ed was a boon, but I do wish there had been enough time to explore more courses. Environmental Bio is not a regret. Not having enough time for Chem is.

No, I do not work now. My family, both immediate and extended, had a cascade of medical crises. I was in the best position to be caregiver. For the past 20 years, I've forgotten my times tables while learning about life through the dignity they've maintained in death.

John, I'm new to online Q&A. I hope you won't be offended if I am not as "chatty" as most here. I haven't yet mastered a conversational typing tone. I'll never be offended when you talk with me. I'm still learning to be an online community member.

I do wish there were more substantive questions here to discuss.

Well, that was probably too much of an introduction!
John McCann
John McCann commented
Especially math. Most students will never be beyond mediocre in math, so analogizing problems is how they will get through the math courses they take.

I have been retired for some time so q and a sites take up much of my free time. I am at 12 to 15 of these sites, but most of them do not have many interesting problems, or any problems at all. Some do not allow HW answers and some, like this site , have people actively discouraging HW questions. This site used to have much more in the way of math and science questions. Now those categories can be frozen for days at a time.

Well, I must flit off to quora and see if anything interesting is happening there.

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