What does a Standard Enthalpy with a subscript "c" mean?

Moderators: Chem_Mod, Chem_Admin

Yinhan_Liu_1D
Posts: 51
Joined: Sat Sep 24, 2016 3:00 am

What does a Standard Enthalpy with a subscript "c" mean?

Postby Yinhan_Liu_1D » Thu Jan 19, 2017 1:42 pm

We've learned that enthalpy with subscript f is the standard enthalpy of formation.

What does the "c" mean?

I saw it on HW:8.57.

Appreciate your help; )

Yinhan_Liu_1D
Posts: 51
Joined: Sat Sep 24, 2016 3:00 am

Re: What does a Standard Enthalpy with a subscript "c" mean?

Postby Yinhan_Liu_1D » Thu Jan 19, 2017 1:45 pm

Is it combustion?

Is it opposite to formation?

Miya McLaughlin 2B
Posts: 24
Joined: Wed Sep 21, 2016 2:57 pm
Been upvoted: 1 time

Re: What does a Standard Enthalpy with a subscript "c" mean?

Postby Miya McLaughlin 2B » Thu Jan 19, 2017 2:12 pm

The subscript "c" on the delta H denotes that it's the Standard Enthalpy value for a combustion reaction. A combustion reaction is when a compound burns completely with O2 gas to create CO2 and H2O. Here is an example.

Ex: 2 C2H2(g) + 5 O2(g) --> 4 CO2(g) + 2 H2O(g)

It's not the exact opposite of formation. Formation is reacting to create one mole of a compound from it's elements. Here is an example.

Ex: 2 C(s) + H2(g) --> C2H2(g)

The Standard Enthalpy of Formation(subscript f) and the Standard Enthalpy of Combustion(subscript c) are different values.


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 2 guests