Chapter 16: Reaction Energy Flashcards

A set of vocabulary flashcards covering the key terms and concepts of thermochemistry, enthalpy, entropy, and free energy as presented in the lecture notes.

Thermochemistry

The study of the transfers of energy as heat that accompany chemical reactions and physical changes.

Chemical energy

A form of potential energy that a substance has available to do work during a chemical reaction, contained in chemical bonds.

Law of conservation of energy

A fundamental law of science stating that energy can neither be created nor destroyed; it can only change forms.

Calorimeter

An insulated vessel used to measure the energy absorbed or released as heat in a chemical or physical change.

Temperature

A measure of the average kinetic energy of the particles in a sample of matter.

Joule

The SI unit of heat as well as all other forms of energy, abbreviated as $J$ and derived from units for mass, distance, and time: $J = kg \times \frac{m^2}{s^2}$.

Heat

The energy transferred between samples of matter because of a difference in their temperatures.

Specific heat ($c_p$)

The amount of energy required to raise the temperature of one gram of a substance by one degree Celsius ($1\,^\circ C$) or one kelvin ($1\,K$).

Enthalpy ($H$)

The quantity representing the energy absorbed as heat during a chemical reaction at constant pressure.

Enthalpy change ($\Delta H$)

The amount of energy absorbed by a system as heat during a process at constant pressure, defined by the equation $\Delta H = H_{\text{products}} - H_{\text{reactants}}$.

Enthalpy of reaction

The quantity of energy transferred as heat during a chemical reaction, representing the difference between the stored energy of the reactants and products.

Thermochemical equation

An equation that includes the quantity of energy released or absorbed as heat during the reaction as written.

Exothermic reaction

A reaction where energy is released, resulting in products having less energy than reactants and a negative enthalpy change ($\Delta H$).

Endothermic reaction

A reaction where energy is absorbed, resulting in products having a larger enthalpy than reactants and a positive enthalpy change ($\Delta H$).

Molar enthalpy of formation ($\Delta H_f^0$)

The enthalpy change that occurs when one mole of a compound is formed from its elements in their standard state at $25\,^\circ C$ and $1\,atm$.

Enthalpy of combustion ($\Delta H_c$)

The enthalpy change that occurs during the complete combustion of one mole of a substance.

Hess’s law

The law stating that the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process.

Entropy ($S$)

A measure of the degree of randomness or disorder of the particles, such as molecules, in a system.

Free energy ($G$)

A combined enthalpy-entropy function, also called Gibbs free energy, that assesses the tendencies for enthalpy and entropy to change for a system at a given temperature and constant pressure.

Free-energy change ($\Delta G^0$)

The difference between the change in enthalpy ($\Delta H^0$) and the product of the Kelvin temperature and the entropy change ($T\Delta S^0$) according to the equation $\Delta G^0 = \Delta H^0 - T\Delta S^0$.