Standard Reaction Enthalpy Definition

[Ricardo Ruiz Flores 1D]

In lecture, I wrote down that Standard Reaction Enthalpy is defined at 1 atm if it's in a gas state (1 M if in a solution) and of elements in their most stable forms.

I wasn't sure if I misheard Dr. Lavelle when he discussed the temperature of 298 Kelvin / 25 degrees Celsius; does standard reaction enthalpy have to be at this temperature?

[Virpal Gill 1B]

No the definition of standard states doesn't include temperature so a standard state can exist at any temperature.

[Nicole 1F]

I don't think that it has to always be at that temperature. A majority of the times, it is at 25 degrees Celsius/298 Kelvin. However, the temperature can vary if the reaction is stated at a specified temperature of interest.

[McKenna disc 1C]

So it can be at any temperature, so long as the substances are existing in their standard state? Thanks!

[Hazem Nasef 1I]

So it can be at any temperature, so long as the substances are existing in their standard state? Thanks!

Yes, that is correct. However, most of the time, the reported data is for 25 degrees celsius.

[Emily Oren 3C]

Also, Dr. Lavelle said that standard reaction enthalpy is at 1 atm, but my TA said it was at 1 bar. Which is it?

[Nathan Tu 2C]

For the standard reaction enthalpy definition, it does not matter what the pressure or temperature is. It refers to a specific reaction enthalpy value at a constant pressure and constant temperature. Naturally, this implies that the values change with temperature and volume. However, most people just use 25 C and 1 atm.

[AnuPanneerselvam1H]

No it does not have to be at this temperature but most reactions happens at 25 degrees Celsius