Chemistry in Energy Generation: Chemical Energy, Fuels, and Bonding

Practice vocabulary flashcards reviewing chemical energy, covalent bond mechanics, Lennard-Jones potential parameters, bond strength values, and thermochemical reaction calculations.

Covalent Bond

A chemical bond that arises from the mutual attraction of two nuclei for the same electrons, resulting in electron sharing and a balance of attractive and repulsive forces.

Two-Centre Two-Electron Bond

A covalent linkage conventionally represented in shorthand notation by dashes between chemical element symbols.

Lennard-Jones Potential

A mathematical model describing the potential energy of interaction between two atoms as a balance of attractive forces (a negative term) and repulsive forces (a positive term), represented by V_{LJ} = \begin{pmatrix}\frac{r_m}{r}\right)^{12} - 2\begin{pmatrix}\frac{r_m}{r}\right)^6.

$r$ (in Lennard-Jones Potential)

The variable representing the distance between interacting atoms.

$r_m$ (in Lennard-Jones Potential)

The specific internuclear distance between two atoms at minimum potential energy.

Bond Formation

The process occurring when two atoms come together to create a bond, which always emits, evolves, or releases energy and is inherently exothermic.

Bond Dissociation

The process wherein two atoms in a bond separate, which always requires energy and is inherently endothermic.

Bond Strength

The quantity of energy required to break a chemical bond.

Bond Length of $H_2$

The internuclear distance between the two hydrogen atoms at minimum potential energy, equal to $74\,pm$.

Bond Energy of $H_2$

The energy needed to break the single $H-H$ bond, equal to $436\,kJ\,mol^{-1}$.

Exothermic Reaction

A chemical reaction in which the energy released from forming new bonds is greater than the energy required to break existing reactant bonds, resulting in heat being given out.

Endothermic Reaction

A chemical reaction in which the energy required to break bonds is greater than the energy released when new bonds are formed.

Combustion of Methane

The reaction $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$, requiring $2648\,kJ\,mol^{-1}$ to break bonds and releasing $3342\,kJ\,mol^{-1}$ as new bonds form, making it net exothermic.

Chemical Energy in Fuels

Energy released during combustion because the energy required to break $C-C$ and $C-H$ bonds in fuel molecules is less than the energy released when very strong $C=O$ and $O-H$ bonds form in $\text{CO}_2$ and $\text{H}_2\text{O}$.

Hydrogenation of Propene

The addition reaction of propene with hydrogen which results in $126\,kJ\,mol^{-1}$ of energy being evolved.

Reaction of $\text{H}_2 + \text{Br}_2 \rightarrow 2\text{HBr}$

The reaction of hydrogen and bromine to yield hydrogen bromide, which evolves $23\,kcal\,mol^{-1}$ of energy based on the given bond energies of $105\,kcal\,mol^{-1}$ ($H-H$), $46\,kcal\,mol^{-1}$ ($Br-Br$), and $87\,kcal\,mol^{-1}$ ($H-Br$).