# Calculating First Ionization Energy

1. Oct 23, 2009

### burg25

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. Oct 24, 2009

### PhaseShifter

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?

3. Oct 24, 2009

### Staff: Mentor

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

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