are systems always measured at equilibrium?

[Andie Jian 1D]

In class, we did the example: "an exothermic rxn (change in enthalpy = -50kJ) occurs in an open beaker producing net 8 moles of gast at 25C. What is the change in internal energy?" We assumed that there was no temperature change, because the temperature is taken before and after the reaction, meaning it already reached equilibrium. However, this sort of confuses me. Do we always assume the measurements are taken at equilibrium? Also, why are temperatures at equilibrium always the same?

[Raquel Ruiz 1K]

We only assume that the temperature is unchanged when it is an isothermal process which means that the temperature is unchanged. Unless they tell you that the temperature is not constant than we use a different equation for the problem. And I'm not sure why the temperature is always assumed to be 25 C or 298K. But I think that if they don't give you a temperature it is safe to say it is an isothermic reaction.

[emily gao 1C]

its usually at 25 celsius bc that's the temp that the scientists got all the standard value table measurements from. eg delta H standard (H2) at 25 degrees C