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Gas and Equilibrium Questions

  1. Nov 6, 2005 #1
    Please make your best effort to answer my questions. There are the select few i did not get from two chapters of homework.

    1.) (See attachment).

    I'm not quite sure how to work with this question. I assume i must use partial pressures. But don't really understand how to start. I assure you i made an honest attempt to do this question, but really can't figure it out.

    2.) A mixture initially consisting of 2 mol CO and 2 mol H2 comes to equilibrium with methanol. At equilibrium, what happens to the amount (in mols; e.g. less than 1 mol, more than 1 mol) of CH3OH?

    I assume that there will be less than 1 mol of CH3OH, but can not figure out how to put this into words. Could anyone explain why?

    3.) At 850 degrees and 1.0 atm pressure, a gas mixture is in equilibrium is 90.55% CO by mass.

    So: C(s) + CO2 (g) <--> 2CO(g)

    Calculate Kc.

    I assumed 100g of mixture. Therefore, there is 90.55 grams of CO, which can be converted into mols (3.2 mols). By using ratios, i conclude that there is 1.6 C and 1.6 mol of CO2. But this doesn't seem right and does not give me the correct answer.

    4.) If i am told that in an equilibrium, the reactant (e.g. 10 mols in 1 L) dissociates to an extent of e.g. 9.5 percent, am i saying that the initial concentration is 10, and that the equilibrium concentration of that reactant is 10 - 0.095*10 ?

    Thank you very much.

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  3. Nov 6, 2005 #2


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    1. From the pressure and volume of the reactants can you calculate the number of moles of each (at 300K) ? Now look at the stoichiometry, from the balanced equation, and determine which of the reactants (if any) is only partially consumed. Next find the number of moles of the product formed and use the ideal gas law once again to find the total pressure. Give it a shot and get back...
  4. Nov 8, 2005 #3
    Thanks gokul.

    Can anyone attempt to answer my other questions?
  5. Nov 11, 2005 #4


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    2. Write out and balance the equation for the reaction between CO and H2 giving CH3OH. Then use stoichiometric relations to determine the qualitative nature of the equilibrium concentrations.

    Do, the first part, and if you're stuck, show what you've done, and we'll take it from there.
  6. Nov 11, 2005 #5


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    3. You misunderstood how the stoichiometric relations work...and this misunderstanding to common to too many students that don't get taught this correctly. I strongly recommend you go over all the worked examples in your text.

    For this problem : you have the number of moles of CO calculated from the mass. Since the rest of the mass of gas (9.45 g) is CO2, you can similarly find the number of moles of CO2. From these two numbers you should be able to calculate Kc.

    4. Yes, your understanding here is correct.
    Last edited: Nov 11, 2005
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