Thermodynamics and Energy

Vocabulary practice flashcards covering thermodynamics, state functions, laws of thermodynamics, Gibbs free energy, redox reactions, and ATP energetics from Chapter 8.

Thermodynamics

The branch of science describing the macroscopic properties of chemical reactions, including whether or not a reaction will occur, but not how quickly it occurs.

State function

A thermodynamic property that depends solely on the current state of a reaction or system, rather than the pathway taken to reach that state.

Enthalpy ($H$)

A thermodynamic state function that represents the potential energy stored within a chemical system.

Enthalpy change ($\Delta H$)

The difference in enthalpy between products and reactants ($\Delta H = H_{\text{prod}} - H_{\text{reac}}$), which corresponds to the heat generated or absorbed during a reaction.

Exothermic reaction

A chemical reaction that releases heat to its surroundings, characterized by $\Delta H < 0$, which tends to be spontaneous.

Endothermic reaction

A chemical reaction that absorbs heat from its surroundings, characterized by $\Delta H > 0$.

First Law of Thermodynamics

The physical principle stating that energy cannot be created or destroyed, only transferred or transformed.

Second Law of Thermodynamics

The physical principle stating that the entropy of an isolated system always increases over time.

Entropy ($S$)

A thermodynamic state function measuring the degree of disorder, randomness, or dispersal of energy within a system.

Entropy change ($\Delta S$)

The change in disorder between products and reactants ($\Delta S = S_{\text{prod}} - S_{\text{reac}}$), where $\Delta S > 0$ indicates products are less ordered and $\Delta S < 0$ indicates products are more ordered.

Spontaneous reaction

A reaction that proceeds on its own without requiring an input of energy, occurring consistently when potential energy decreases ($\Delta H < 0$) and disorder increases ($\Delta S > 0$).

Gibbs Free Energy ($G$)

The total energy in a reaction available to perform work, calculated by the equation $\Delta G = \Delta H - T\Delta S$, where $T$ is temperature in Kelvin.

Exergonic reaction

An energetically favorable, spontaneous reaction that releases energy and is characterized by $\Delta G < 0$.

Endergonic reaction

An energetically unfavorable, nonspontaneous reaction that requires energy input and is characterized by $\Delta G > 0$.

Energetic coupling

The biological process in which free energy released by an exergonic reaction is used to directly drive an endergonic reaction, typically via electron transfer or phosphate group transfer.

Reduction

The gain of electrons by an atom or molecule during a chemical reaction.

Oxidation

The loss of electrons from an atom or molecule during a chemical reaction.

Redox reaction

A coupled chemical process wherein one molecule undergoes oxidation (loss of electrons) while another simultaneously undergoes reduction (gain of electrons).

Oxidizing agent

A chemical species that acts as an electron acceptor, oxidizing other molecules while becoming reduced itself (such as $O_2$).

Reducing agent

A chemical species that acts as an electron donor, reducing other molecules while becoming oxidized itself.

Adenosine triphosphate (ATP)

A nucleotide and universal high-energy molecule consisting of adenine, ribose, and three phosphate groups that drives endergonic cellular reactions through phosphate group transfer.

Phosphoanhydride bonds

The high-energy chemical bonds connecting the adjacent phosphate groups in ATP whose hydrolysis yields substantial free energy.

Inorganic phosphate ($P_i$)

The cleaved phosphate product of ATP hydrolysis whose resonance stabilization and solvation energetically favor the forward reaction.