Calculate the change in enthalpy ( DeltaH) for the chemical reaction modeled by this chemical equation: H_2 + Cl_2 rarr 2HCl Is energy entering or leaving the system? How do you know? What happens to the covalent bonds during this reaction?

May 4, 2017

The enthalpy change is established by MEASUREMENT.......

Explanation:

And I don't know offhand how they measured the enthalpy change for the reaction,

${H}_{2} \left(g\right) + C {l}_{2} \left(g\right) \rightarrow 2 H C l \left(g\right) + \Delta$

but such a measurement could conceivably be done and no doubt has been done.

Bond enthalpies are, however, extensively tabulated, and these can be used to estimate the enthalpy change of a given reaction with a high degree of precision. See here for an example.