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Homework Help: Enthalpy and heat transfer problem

  1. May 28, 2007 #1
    THe question is :

    Given the reaction

    CH3OH goes to CO + 2H2 Change in heat=90.7
    a)endothermic or exothermic?
    b)Calculate amount of heat transferred when 45 g. of CH3OH id decomposed by this reaction at constant pressure.
    c)For a given sample of CH3OH the enthalpy change on reaction is 18.5kJ. How many grams of hydrogen gas are produced?
    d)What is the value of delta H for the reverse of the previous reaction? How many kJ of heat are released when 27 g of CO reacts completely with H2 to form CH3OH at constant pressure?

    I can do a and b. I am stuck on c and d. I know for c I need to determine the amount of moles of CH3OH involved in the reaction but am stumped at how to do that.

    Same with d. I think I need to determine the amount of CO moles then multipy by the heat involved per mole of the CO from the given reaction. Can't seem to be able to do it though. I know what needs to be done but can't do it!
  2. jcsd
  3. May 29, 2007 #2
    This doesn't mean anything: "Change in heat=90.7"
  4. May 29, 2007 #3

    delta + 90.7 is what it reads in the question
  5. May 29, 2007 #4
    For part c could you use the eqation: delta H = q/n
    to find the number of moles used where q is the heat change?

    Hope this helps but im not sure if it will!!!
  6. May 29, 2007 #5


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    '90.7' what? Calories? Joules? Perhaps this is molar enthalpy in kJ/mol?

    If so, 'c' can be related to this (in moles) by dividing 18.5 kJ by 90.7 kJ/mol to get # of moles of CH3OH.

    for 'd' you can use the same logic.
    Hint: CH3OH goes to CO + 2H2 means:

    CH3OH + 90.7 kJ ------> CO + 2H2

    Notice the relationship to the number of moles of CO and CH3OH?
    Last edited: May 29, 2007
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