Standard state

[Natalie Bender]

Hi! I have in my notes that most reactions are given in their standard states, but if the reaction isn't given in its standard state, how do we find what that is?
Thanks!

[liamtran]

Determining the enthalpy of a reaction in its non-standard state would involve using the given reaction along with documented standard enthalpies of physical change (fusion, vaporization) to account for any differences in phase among the species.
i.e., if a reaction is given as A(s) -> B(l), and the reaction in its standard is given as A(s) -> B(s), adding the enthalpy of formation with the enthalpy of freezing
(-Hfus) for B: B(l) -> B(s) would produce the total enthalpy.

[905775469]

Adding on to this question does standard state mean pressure and volume are constant with standard state enthalpies.

[Layla Shapouri 2L]

Yes, the standard state requires the everything to be at the standard pressure, temp etc.

[AliciaRoice_1K]

Standard states refer to standard temperatures and pressure in a chemical reaction. You may have heard this being referred to as STP (standard temperature and pressure), in CHEM14A, where the temperature is at 0 degrees Celsius and the pressure is at 1 atm.

[Keanu Ngo 3B]

If a chemical reaction does not include reactants in their standard states, you have to find the change in enthalpy to change the reactant from its standard state to the state given in the reaction. Once you have calculated that, you must include in your calculation of overall enthalpy.

[Audrey2B]

Is the bond enthalpy for a molecule in its standard state 0?

[Isabelle Kim 3E]

The standard state of any solid or liquid substance are defined to be the most stable form found at a pressure of one bar. Basically, the standard states of any substance would be its phase at 25 degrees celsius and one atmospheric pressure.