Understanding Heat of Atomization: Equations and Problem-Solving Techniques

[Lori]

Homework Statement

So, my textbook doesn't go over these type of problems for heat of atomization , so I am confused on how to write the chemical equations for them.

Question: The heat of atomization is the heat needed to separated gaseous atoms from a substance in its standard state. The equation for the atomization of graphite is C(graphite) --> C(gas)

Homework Equations

Given,
1) Heat of formation for CH4 = -74.9 Kj/mol
2)Heat of atomization for CH4 = 1660 kj/mol
3) heat of atomization for H2 = 423 kj/mol

The Attempt at a Solution

For the equation number 1, i got C(graphite) + 2H2 -> CH4(s)
for number 2, i got C(graphite) + 4H -> C(g) + H(g)
For 3, i got 1/2H2(g) --> H(g)

I'm not sure if the second one is write. I was thinking that if i was able to write the equations correctly, then i can do some cancellation so i get C(graphite) --> C(gas).

 

[Borek]

CH₄ is not solid (check your first equation). In the second you should have just CH₄(g) on the left, not some combination of separated elements.

 

[Lori]

CH₄ is not solid (check your first equation). In the second you should have just CH₄(g) on the left, not some combination of separated elements.

CH₄ is not solid (check your first equation). In the second you should have just CH₄(g) on the left, not some combination of separated elements.

So it should look like this?

C(graphite) + 2H2(g) -> CH4(g)
CH4(g) -> C(g) + H(g)
1/2H2(g) --> H(g)

How would the kj/mol change for each equation? Would they remain the same?

 

[Borek]

First two equations look OK, I think the last one should be doubled - it is about atomizing a molecule, not half of the molecule. But in general you should check what definition you were given, as these things are often ambiguous.