Chemistry Practice Problems Bond Energy Practice Problems Solution: Calculate the magnitude of the enthalpy change, an...

Solution: 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

Problem

Calculate the magnitude of the enthalpy change, and determine if the reaction is exothermic or endothermic for the following reaction: NH3 + 3F2 ⟶ NF3 + 3HF

A. 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

Solution

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:

ΔH°rxn = Hbond reactants - Hbond 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:


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