If the  of a reaction is less than zero, the reaction will in fact be exergonic. These reactions will be favorable and spontaneous, and energy is released in these reactions. Thus, endergonic is incorrect. 

The temperature and pressure of the reactants and products of any given reaction will determine the value of . However, this is entirely dependent of the reaction rate, which is determined by how the concentrations of the reactants and products change over the course of the reaction. Additionally, every reaction is unique, so "one-half" or any other exact metric cannot be applied as the definition. 

In equilibrium, both the forward and reverse reactions continue to occur, but they do so in a way that is equal and thus, there is no net change of reactants and products in the system.  is zero in this case because net changes to the system have ceased, and thus the free energy is no longer in flux.

Exothermic reactions release heat (think exothermic = explosion = creates heat), and this is due to the release of energy from the reactant bonds. These reactions have  less than zero. Endothermic reactions are just the opposite and actually require energy to occur, and therefore do not occur spontaneously nor release heat. 

A hydrogen bond is the weak attraction of a covalently bonded hydrogen to nearby fluorine, oxygen, or nitrogen (FON) atoms. These attractions can occur within a single molecule (intramolecular) or between two distinct molecules in close proximity (intermolecular). Hydrogen bonds give water its cohesiveness and its surface tension. 

Ionic bonds form when one or more electrons from an atom are removed and attached to another atom resulting in positive and negative ions that attract each other. Sodium chloride is an example of an ionic compound. Covalent bonds form when one or more pairs of electrons are shared by two atoms. Hydrochloric acid is an example of a covalent compound. A hydrogen bond is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity (oxygen, nitrogen, or fluorine) in another molecule. Water molecules are capable of intermolecular hydrogen bonds. A dipole-dipole bond is an attractive force between the positive end of one polar molecule and the negative end of another polar molecule. Iodine monochloride molecules show dipole-dipole attraction. Van der Waals forces arise from spontaneous changes in electron density; these occur in all chemical molecules regardless of composition and are extremely weak interactions.

Energy is absorbed when bonds break. The energy required to break the bond is absorbed from the surroundings. You have to put energy into a molecule to break its chemical bond.

Energy is released when bonds form. Bond formation represents a stable configuration of atoms. If breaking a bond absorbs energy, forming a bond must release energy; thus, the mnemonic BARF—Break (a bond), Absorb (energy), Release (energy), Form (a bond).

SCAN is the mnemonic for the magnetic field induced in a coil—south clockwise, anticlockwise north. PASS stands for pull, aim, squeeze, sweep—how to use a fire extinguisher. RICE is the treatment for an injury to a joint: rest, ice, compression, elevation. LEO says GER is a mnemonic for loss of electrons is oxidation, gain of electrons is reduction. 

Since hydrochloric acid has a partial positive charge on the hydrogen and a partial negative charge on the chlorine, the molecules will have dipole-dipole interactions between them. Although hydrogen bonding is a stronger force, a hydrogen must be attached to a nitrogen, oxygen, or fluorine in order to exhibit hydrogen bonding.

Hydrogen bonding is possible when a hydrogen atom is attached to a nitrogen, oxygen, or fluorine. Of the following options, hydrochloric acid  is the only option that does not fit the criteria.

Oxidation is the process of losing electrons, or acquiring a more positive charge. We can determine which atom has lost electrons by comparing the oxidation number of the atom as a reactant and as a product. Aluminum is in elemental form as a reactant, so it has an oxidation number of 0. As a product, it is bonded with oxygen, giving each aluminum an oxidation number of +3. Since it has a more positive charge, the aluminum has been oxidized.