[soccer05]

H2 (g) + F2 (g) ----> 2HF

Delta H° = -271 kJ/mol

If H2 (g) and F2 (g) are mixed, how could you determine what type of reaction it would be?

Exothermic or endothermic? And will the temperature of the reaction rise or fall?

Or can it not be determined unless the intiial and final temperatures are given?

[DevaDevil]

Almost all you need to know is given, namely the dH(adiabatic); adiabatic means no heat exchange outside the system. You just need to know if the pressure is constant now.

If the system is adiabatic and at constant pressure:
Then it is just knowing about the definition of exo- and endothermic, learn it!

If the enthalpy change of the reaction is negative; in other words energy is released: Exothermic.
If the enthalpy change of the reaction is positive; in other words energy is consumed: Endothermic.

Temperature change in reaction is part of that definition: Endothermic (energy consumed): fall of T; Exothermic (energy released): rise of T.