Problem: Calculate the magnitude of the enthalpy change, and determine if the reaction is exothermic or endothermic for the following reaction: NH3 + 3F2 ⟶ NF3 + 3HFA. 870.9 kJ mol–1 , exothermic B. 870.9 kJ mol–1 , endothermic C. 1112 kJ mol–1 , exothermic D. 1112 kJ mol–1 , endothermic E. 290.3 kJ mol–1 , endothermic

We are asked to calculate the magnitude of the enthalpy change, and determine if the reaction is exothermic or endothermic for reaction. 

To calculate the ΔH°_rxn using bond energies, we’re going to use the following equation:

$\boxed{\mathit{\Delta }\mathit{H}{\mathbf{°}}_{\mathbf{rxn}\mathbf{ }}\mathbf{=}\mathbf{ }{\mathit{H}}_{\mathbf{bond}\mathbf{ }\mathbf{reactants}}\mathbf{ }\mathbf{-}\mathbf{ }{\mathit{H}}_{\mathbf{bond}\mathbf{ }\mathbf{products}}}$

Let’s first figure out what kind of bonds and how many moles are present in each reactants and products because the given bond energies are per mole.

Balanced Reaction:  NH₃ + 3F₂ ⟶ NF₃ + 3HF

*always make sure that the given reaction is balanced

Draw the structure of each compound.

Reactants:

• NH₃: