Enthalpy change question

[FeralisExtremum]

I'm having a bit of an issue with this Qvault question on enthalpy:

According to Chad, any element in its standard state, will have a ΔHf of 0 by definition. That would lead me to think the ΔHf of this reaction is just 165.2. According to Qvault: "The enthalpy change is represented by the following equation ΔH rxn = ΔH products - ΔH reactants. So the answer is ΔH=(165.2)−(29.2+97.7). This is equal to 38.3 kJ/mol"

I understand the math they used, but why do Ni and Cl2 (being in their standard states) not have a ΔHf of 0?

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[DAT Destroyer]

I'm having a bit of an issue with this Qvault question on enthalpy:

According to Chad, any element in its standard state, will have a ΔHf of 0 by definition. That would lead me to think the ΔHf of this reaction is just 165.2. According to Qvault: "The enthalpy change is represented by the following equation ΔH rxn = ΔH products - ΔH reactants. So the answer is ΔH=(165.2)−(29.2+97.7). This is equal to 38.3 kJ/mol"

I understand the math they used, but why do Ni and Cl2 (being in their standard states) not have a ΔHf of 0?

You are correct....Ni and Cl2 are BOTH in the standard state,,, hence the Heat of Formation is ZERO. Do yourself a favor...and use a textbook written by a PhD chemist. I like the Raymond Chang book......It is virtually error-free.

Hope this helps.

Dr. Jim Romano

 

[FeralisExtremum]

You are correct....Ni and Cl2 are BOTH in the standard state,,, hence the Heat of Formation is ZERO. Do yourself a favor...and use a textbook written by a PhD chemist. I like the Raymond Chang book......It is virtually error-free.

Hope this helps.

Dr. Jim Romano

Thank you!

 

[Dentalogist]

that looks pretty hard...(college freshmen here)

 

[O Gaúcho]

You should learn this in general chemistry.

 

[eugpeng]

they're asking for enthalpy change not enthalpy of formation. If it was formation the standard states would be 0

 

[FeralisExtremum]

they're asking for enthalpy change not enthalpy of formation. If it was formation the standard states would be 0

But the numbers they provided are under the column "ΔH of formation"...

 

[Master Yoda]

I'm having a bit of an issue with this Qvault question on enthalpy:

According to Chad, any element in its standard state, will have a ΔHf of 0 by definition. That would lead me to think the ΔHf of this reaction is just 165.2. According to Qvault: "The enthalpy change is represented by the following equation ΔH rxn = ΔH products - ΔH reactants. So the answer is ΔH=(165.2)−(29.2+97.7). This is equal to 38.3 kJ/mol"

I understand the math they used, but why do Ni and Cl2 (being in their standard states) not have a ΔHf of 0?

WOW! I would suggest you stick to the Biology section of Qvault. Their chemistry section has tons of error. Or you could stick to a textbook like Dr. Romano suggested. I would go with the recommended textbook from AADSAS website: Chemistry the Central Science.

 

[O Gaúcho]

Chemistry The central science also has a TON of errors. I am currently taking gen chem II and our teacher gives us a few points for every error found in the NEW 2014 version of the textbook. I have already found over 15 errors. And the class a total probably has found over 100 errors. But despite all these errors, it is a great textbook.

 

[DAT Destroyer]

WOW! I would suggest you stick to the Biology section of Qvault. Their chemistry section has tons of error. Or you could stick to a textbook like Dr. Romano suggested. I would go with the recommended textbook from AADSAS website: Chemistry the Central Science.

I recommended the book by Raymond Chang

Dr. Romano