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Please help with equilibrium problem

  1. Apr 7, 2005 #1
    I have been trying to this problem for an hour now and i have no clue what to do and where to start.

    Given equation- 2NaHCO3(s)<-->Na2CO3(s)+H2O(g)+CO2(g)
    a. A sample of 100 grams of solid NaHCO3 was placed in an 5 L container and heated to 160 degrees C. Some of the original solid remained and the total pressure in the container was 7.76 atmospheres when equilibrium was reached. Calculate the number of moles of H2O present at equilibrium. (NaHCO3 molar mass= 84 g, PV=nRT, R=.08206 L atm/mol K)
    b. How many grams of the original solid remain in the container under the conditions described in "a"?
    c.Write the equilibrium expression for the equilibrium constant Kp and calculate its value for the reaction under the conditions in "a".
    d. If 115 g. of solid NaHCO3 had been placed in the 5 L container and heated to 160 degrees C, what would have the total pressure been at equilibrium?
  2. jcsd
  3. Apr 7, 2005 #2


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    Where to start : write and balance the equation for the decomposition of sodium bicarbonate.
  4. Apr 7, 2005 #3
    how do you do that?
  5. Apr 8, 2005 #4


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    You need to figure that out way before you start solving problems in chemical equilibrium. In this case, that part has already been done for you.

    You need to get your basics first. There's no way you can solve these problems without knowing how to balance chemical equations. A suggestion : read your text.
  6. Apr 8, 2005 #5

    First of all when an equation is given to you, check to see whether it's balance. Equations hold key information like stoichiometric proportions in a reaction.

    e.g. check to see whether 2 atoms of Na on the left corresponds to 2 atoms of Na on the right, and so on for the rest of the elements.

    From the ideal gas equation PV = nRT with some information given to you like pressure, temperature etc. What is the unknown in the equation? Don't forget that you R constant is in L.atm/mol.k

    Hope this helps you to start. :smile:
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