Calculating heat from H2 and O2

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Discussion Overview

The discussion revolves around calculating the heat produced from the combustion of hydrogen and oxygen. Participants explore the relationship between the amounts of reactants and the energy released during combustion, including considerations for different molar ratios and the implications for energy calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states that the enthalpy of combustion for the reaction 2H2 + O2 → 2H2O is 287 kJ/mol, suggesting this value can be used for calculations.
  • Another participant emphasizes that if the molar ratio of hydrogen to oxygen differs from 2:1, complete combustion may not occur, affecting the energy extracted.
  • Some participants propose that the heat of combustion for hydrogen can be multiplied by the number of moles of hydrogen to find the total heat energy produced.
  • Questions are raised about how to handle scenarios where the molar ratio is not 2:1, including inquiries about calculating energy in such cases.
  • One participant asks whether the heat of combustion of other elements can be added to that of hydrogen when mixed, indicating a need for clarification on this point.
  • A separate question is posed regarding how to calculate temperature from the heat energy produced, noting the potential need for initial temperature as a factor.

Areas of Agreement / Disagreement

Participants generally agree on the basic principles of calculating heat from combustion but express uncertainty regarding the implications of varying molar ratios and how to approach calculations in those cases. The discussion remains unresolved on several points, particularly regarding the treatment of other elements in combustion and the relationship between heat energy and temperature.

Contextual Notes

Limitations include the lack of detailed examples for varying molar ratios and the dependence on specific definitions of combustion and heat of combustion. There are also unresolved questions about the calculation of temperature from heat energy.

Who May Find This Useful

This discussion may be useful for students and practitioners in chemistry and engineering fields, particularly those interested in combustion processes and thermodynamics.

Butterfly_grl
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It is known that Hydrogen and Oxygen when combined can combust of course. So my question is : Can I calculate the heat produced from this combustion if I put a certain amount of hydrogen and oxygen?

Please Explain with an example.
 
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Butterfly_grl said:
It is known that Hydrogen and Oxygen when combined can combust of course. So my question is : Can I calculate the heat produced from this combustion if I put a certain amount of hydrogen and oxygen?

Please Explain with an example.

You certainly can calculate it. Since all H2/O2 molecules are identical, the same amount of energy will be released each time and so we can just quote a standard value from a textbook. I presume the reaction you have in mind is

2*H2 + O2 --> 2*H2O

which according to http://en.wikipedia.org/wiki/Hydrogen" has an enthalpy of combustion equal to 287 KJ/mol.

If you have a molar ratio different from 2:1 then complete combustion is impossible and the amount of energy you can extract will differ.
 
Last edited by a moderator:
Google "heat of combustion hydrogen", then multiply that number by the amount of hydrogen you have.
 
Alewhey said:
If you have a molar ratio different from 2:1 then complete combustion is impossible and the amount of energy you can extract will differ.

I think I understand this part but I've got a couple of questions.

1. When you say "complete combustion is impossible" that doesn't mean there's no combustion, there is but with a less or more amount. Right?

2. if such thing (molar ratio diffrent than 2:1) happened how can I calculate the energy then.

Again could you give me an example.

Thanks a lot.
 
russ_watters said:
Google "heat of combustion hydrogen", then multiply that number by the amount of hydrogen you have.

If I have the amount of hydrogen ( number of moles ) then I can calculate the heat energy. Ok, but let me get this right.. We didn't mention the oxygen because it doesn't have heat of combustion, but if I mix the hydrogen with any element that has heat of combustion I'll just add them to get the final heat of combustion. SO Is that right?
 
Another Question :

How can you calculate the temperature when you have the heat energy? I think of course it needs another factor like the "initial temprature" but I don't know...

Thanks
 

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