AboutScienceAdviser Expertise Expertise: I can answer questions about biochemistry, molecular biology, physics, chemistry, biology, genetics, applying for graduate school, assays, protocols, grants, experiments. I do answer questions at night since I am in the lab working during the day. Also, to be fair to every one, I do one follow ups and if you are interested in more, please contact me under:
http://www.liveperson.com/tutor09. It will allow me to be in a live chat with you so we can communicate more effeciently, and I can understand your issues and help you better.
Experience Biochemistry and Molecular Biology, but I do my best to help you with any general science questions at any level.
Organizations please visit me at http://www.liveperson.com/tutor09. It will allow me to be in a live chat with you so we can communicate more effeciently, and I can understand your issues and help you better.
Credentials Ph.D, but currently doing my postdoctoral training at Havard Medical School teaching hospital in cancer biology
Question QUESTION: OK - here is the set - up. Question is way at the bottom but you need this set-up to understand my question.
ΔHf methane is represented by the equation:
C(s) + H2(g) CH4 (g)
This equation can be constructed using the equations for combustion of the reactants (carbon and hydrogen) and the product (methane)
C(s) + O2(g) CO2(g) -394kj enthalpy 1
And after rearrangement ( take the CH4 to the right hand side) the result is the equation for the formation of methane
C(s) + H2(g) CH4 (g) +13kj enthalpy ( 4 - 5)
I cannot figure out why I have to multiply H2(g) + 1/2O2(g) H2O(l) by two? And why do I start with 1/2 O2 rather than just using O2. THANKS!
ANSWER: Hi there, you usually multiply because you need the equiblrium between the number of atoms that you have in each site. If you use the 1/2 of oxyen you are not able to get one mole of CH4. If you go back and use only 1/2 of oxygen, you will notice that it won't add up to methan that you are looking for.
Please get back to me if my answer is not very clear and you would like me to go back and explain it step by step. I will do that for you.
Best,
Gloria
---------- FOLLOW-UP ----------
QUESTION: Hi Gloria, THANKS. I think I am getting it. The only thing I am still confused about is why I have to start with only 1/2 oxygen rather than using 1 O2 for the combustion of H2 in the first place? How do I know that I have to start by using 1/2 O2? Thank you so much.
Answer Hi there, You are very welcome. I think it is becasue, again, you have to equiblirate your equation. Honestly, most of the time, we were told to use O2 instead of 1/2O2. but if you think about it:
H2 + O2 ---> H2O, you just need one molecular of oxygen in the water, so you go with 1/2 rather than doubling every thing. you get one mole of H2, but you require only 1/2 of oxygen for that.
That is the only reason that came to my mind.
Let me know if you have any more question or it is still not clear to you.
Best
Gloria
