Internal energy refers to the energy of the system. It is equal to sum of the potential and kinetic energies of the particles of the system.
The First Law states that the energy of the universe does not change. Over the course of a chemical reaction, the energy of your system may change. This balances, however, by an equal and opposite change of energy in the surroundings for a net change of zero.
Bond energy is the amount of energy it takes to break a bond. Breaking bonds requires energy input, thus the process is endothermic, meaning energy absorbs. You can calculate the heat of reaction by subtracting the bond energies of those formed in the products, from the bond energies of the bonds broken in the reactants.
The Gibbs free energy (G) of a reaction is the measure of the energy available to do work after the completion of the reaction. Calculating Gibbs free energy requires enthalpy (heat of reaction, H), temperature in Kelvin (T), and the entropy (S). Entropy is a measure of disorder of the system.
The change in free energy for a reaction (ΔG) determines whether or not the reaction will proceed spontaneously. Using the equation ΔG = ΔH - TΔS, where delta refers to the change in any quantity, calculate ΔG for your reaction. If ΔG is a negative number, the reaction is spontaneous. If ΔG is a positive number, the reaction is non-spontaneous.