thermochemistry

Question

Determine heat of formation of CCl4g, at 298K,

CH4 + Cl2 --> CCl4 + 4HCl reaction's, is -397.3kJ

CH4= -78.4 kj

HCl= -92.3

Cl2 = 0

I tried to do the sum of the products - reactents = -397.3 but my answer was still wrong...

Answer 1

What answer did you get that is still wrong? And also, your equation isn't correct. It should read

CH4 (g) + 4 Cl2 (g)==> CCl4 (g) + 4 HCl (g). It won't matter in the end because ∆H for Cl2 is zero, but you should be aware of this. Also, the values for heats of formation should probably be in kJ/mole.

-397.3 =[ (4x-92.3) + x] - [(-78.4) + 0]

-397.3 = -369.2 + x +78.4

-397.3 = x - 290.8

x = -106.5 kJ/mole