Chapter 16: Reaction Energy Flashcards

Vocabulary practiced focused on thermochemistry, enthalpy, entropy, and free energy concepts from Chapter 16.

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 within 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 ($J$)

The SI unit of heat as well as all other forms of energy, defined as $J = \text{kg} \times \text{m}^2 / \text{s}^2$.

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 ($1\,^{\circ}\text{C}$) or one kelvin ($1\,\text{K}$) at a given pressure.

Enthalpy ($H$)

A quantity used to represent 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, calculated as $H_{\text{products}} - H_{\text{reactants}}$.

Enthalpy of reaction

The quantity of energy transferred as heat during a chemical reaction.

Thermochemical equation

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

Exothermic reaction

A chemical reaction where energy is released and the enthalpy change ($\Delta H$) is always negative.

Endothermic reaction

A chemical reaction where energy is absorbed and the enthalpy change ($\Delta H$) is always positive.

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 $25\,^{\circ}\text{C}$ and $1\,\text{atm}$.

Enthalpy of combustion ($\Delta H_c$)

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

Hess's law

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

Energy density

The amount of energy that can be extracted from a given amount of matter, often measured in units of $\text{MJ/kg}$ or $\text{MJ/L}$.

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 at a given temperature and constant pressure.

Free-energy change ($\Delta G$)

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

Spontaneous reaction

A reaction that occurs naturally and results in a decrease in free energy ($\Delta G < 0$).