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Homework Help: Calculating First Ionization Energy

  1. Oct 23, 2009 #1
    1. The problem statement, all variables and given/known data
    I have an exam on Monday and do not know how to do this example problem.

    Use the following information to calculate the first ionization energy of Li.
    LiF(s) → Li+(g) + F −(g) 1050 kJ/mol LiF
    Li(s) + ½ F2(g) → LiF(s) −617 kJ/mol Li
    F2(g) → 2 F(g) 160 kJ/mol F2
    Li(s) → Li(g) 161 kJ/mol Li
    F(g) → F −(g) −328 kJ/mol F

    (a) 520 kJ/mol Li
    (b) 440 kJ/mol Li
    (c) 426 kJ/mol Li
    (d) 346 kJ/mol Li
    (e) 216 kJ/mol Li

    The answer is a but I cant figure out how to get it. If you could show me the process I would greatly appreciate it.

    2. Relevant equations
    H=Bonds Broken - Bonds Formed

    3. The attempt at a solution
    617 = 160 + 161 +1050 + x - 328
    x = 426
    I know this method isn't right because 1. It makes no sense 2. It doesn't follow the bond enthalpy formula
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 24, 2009 #2
    How can you combine the reactions given to have a balanced equation with Li(g) as a reactant and Li+(g) as a product, and all the others as spectators?
  4. Oct 24, 2009 #3


    User Avatar

    Staff: Mentor

    Don't go for bonds, use Hess law (which is basically what PhaseShifter suggests).

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