Free Energy and Entropy

Front

Enthalpy (ΔH) Noun

---

[en-thal-pee]

Back

Enthalpy (ΔH)

---

A measure of the total heat content of a system, where its change indicates if a process is exothermic or endothermic.

---

Example: This diagram shows that adding heat energy causes phase changes, like ice melting and water boiling, which illustrates the concept of enthalpy change (ΔH).

Front

Exothermic Adjective

---

[ek-so-thur-mik]

Back

Exothermic

---

Describes a process that releases energy, usually as heat, into its surroundings, corresponding to a negative change in enthalpy.

---

Example: A combustion reaction, like burning wood, is exothermic because it releases energy into the surroundings as heat and light.

Front

Endothermic Adjective

---

[en-do-thur-mik]

Back

Endothermic

---

Describes a process that absorbs energy, usually as heat, from its surroundings, corresponding to a positive change in enthalpy.

---

Example: The Earth absorbs energy from the sun, an example of an endothermic process where a system (Earth) takes in energy from its surroundings (the Sun).

Front

Combustion Noun

---

[kom-bus-chun]

Back

Combustion

---

A rapid chemical reaction between a substance and an oxidant, like oxygen, that produces both heat and light energy.

---

Example: This diagram shows a combustion reaction, where a hydrocarbon fuel and oxygen (inputs) react to produce heat, light, water, and carbon dioxide (outputs).

Front

Entropy (S) Noun

---

[en-tro-pee]

Back

Entropy (S)

---

A thermodynamic property that serves as a measure of the disorder, randomness, or unpredictability within a given system.

---

Example: This diagram shows that entropy is a measure of disorder. A system moves from a low entropy (ordered) state to a high entropy (disordered) state.

Front

Spontaneous Process Noun

---

[spon-tay-nee-us pro-sess]

Back

Spontaneous Process

---

A process that can occur without a continuous input of external energy after it has been initiated; also called thermodynamically favorable.

---

Example: Adding sugar to hot water causes it to dissolve on its own, spreading the sugar particles evenly to form a solution; this is a spontaneous process.

Front

Nonspontaneous Process Noun

---

[non-spon-tay-nee-us pro-sess]

Back

Nonspontaneous Process

---

A process that requires a continuous input of external energy to proceed; also known as a thermodynamically unfavorable process.

---

Example: Photosynthesis is a nonspontaneous process because it requires a constant input of energy from sunlight to convert carbon dioxide and water into glucose.

Front

Free Energy (G) Noun

---

[free en-er-jee]

Back

Free Energy (G)

---

The portion of a system's total energy that is available to perform useful work, determining the spontaneity of a process.

---

Example: A ball at the top of a hill has stored energy and will roll down on its own. This illustrates how systems with high free energy (G) change spontaneously.

Front

Reaction Rate Noun

---

[ree-ak-shun rayt]

Back

Reaction Rate

---

The speed at which a chemical reaction proceeds, which is a kinetic property independent of its thermodynamic favorability.

---

Example: This graph shows that as a reaction progresses over time, the amount of starting materials (reagents) decreases while the amount of new substances (products) increases.

Front

Kelvin (K) Noun

---

[kel-vin]

Back

Kelvin (K)

---

The SI base unit of thermodynamic temperature, essential for calculations involving the free energy equation and other thermodynamic relationships.

---

Example: This diagram compares the Kelvin and Celsius temperature scales, showing that 0 K is absolute zero, the lowest possible temperature, which is crucial for thermodynamic calculations.