H2 and F2 react according to the following equation, forming HF.

H2(g) + F2(g)  2HF(g); H° = –271 kJ
If H2(g) and F2(g) were mixed in a thermally insulated vessel, the reaction that occurred would be

a. endothermic, and the temperature of the reaction system would fall.
b. We could not tell unless the original and final temperatures were given.
c. exothermic, and the temperature of the reaction system would fall.
d. exothermic, and the temperature of the reaction system would rise.
e. endothermic, and the temperature of the reaction system would rise.

the Answer would that it is exothermic and the temperature of the reaction system would rise

d. exothermic, and the temperature of the reaction system would rise.

To determine the nature of the reaction and the impact on the temperature of the reaction system, we can analyze the given information.

The reaction equation shows that H2(g) and F2(g) react to form 2HF(g) with a negative enthalpy change (∆H° = -271 kJ).

In an exothermic reaction, the system releases heat to the surroundings, resulting in a temperature increase. Conversely, in an endothermic reaction, the system absorbs heat from the surroundings, leading to a temperature decrease.

Since the given reaction has a negative enthalpy change (∆H° = -271 kJ), it indicates that the reaction is exothermic. This means that the reaction will release heat to the surroundings.

Now, since the reaction occurs in a thermally insulated vessel, there is no exchange of heat with the surroundings. Consequently, the heat released by the exothermic reaction will remain within the system.

Based on these observations, we can conclude that the reaction will be exothermic, but the temperature of the reaction system will fall (option c).

Therefore, the correct answer is c. exothermic, and the temperature of the reaction system would fall.

What do you not understand about this?

Exothermic means heat is given off by the system and the surrounding temperature rises.
Endothermic means heat is absorbed by the system and surroundings get cooler.

By convention, a negative sign for dH means that heat is released (given off) and a + sign for dH means heat is absorbed by the system (surroundings get cooler).