Science Assessment

The production of a fertilizer involves the chemical reaction between nitrogen (N₂) and hydrogen (H₂) to form ammonia (NH₃). In the equation for this reaction shown below, blue circles labeled N represent nitrogen atoms and white circles labeled H represent hydrogen atoms. Lines represent bonds between the atoms that make up molecules.

Scientists have determined the amount of energy associated with both breaking and forming the bonds between the atoms that make up the molecules of N₂, H₂, and NH₃. The table below lists the total amount of energy associated with breaking the bonds of the reactant molecules (1 mole of N₂ and 3 moles of H₂) and the total amount of energy associated with forming the bonds of the product molecules (2 moles of NH₃). [A kilocalorie (kcal) is a unit of energy and a mole is a very large quantity of molecules.]

Based on this information, does this reaction give off or take in energy and why?

1. The reaction takes in energy because energy is taken in by all chemical reactions regardless of differences in total bond energy.
2. The reaction takes in energy because the total bond energy of the reactants is less than the total bond energy of the products.
3. The reaction gives off energy because energy is given off by all chemical reactions regardless of differences in total bond energy.
4. The reaction gives off energy because the total bond energy of the reactants is less than the total bond energy of the products.