An overview of the fundamental concepts of chemical thermodynamics, including energy, work, heat, and the laws of thermodynamics.
Introduction to Chemical Thermodynamics
Fundamental concepts, key laws, and practical applications
| Concept | Symbol | Units | Typical Use |
|---|---|---|---|
| System | – | – | Portion of the universe under study (e.g., a reaction flask). |
| Surroundings | – | – | Everything external to the system. |
| State Function | – | – | Property that depends only on the current state (e.g., internal energy, enthalpy, entropy). |
| Path Function | – | – | Property that depends on the process path (e.g., heat q, work w). |
| Enthalpy (H) | (H) | J (or kJ) | Heat content at constant pressure. |
| Entropy (S) | (S) | J K⁻¹ | Measure of disorder or the number of accessible microstates. |
| Gibbs Free Energy (G) | (G) | J (or kJ) | Predicts spontaneity at constant (T) and (P). |
| Internal Energy (U) | (U) | J | Total microscopic energy of a system. |
| Law | Statement (Chemistry Emphasis) | Practical Implication |
|---|---|---|
| Zeroth | If two systems are each in thermal equilibrium with a third, they are in equilibrium with each other. | Enables the definition of temperature. |
| First (Energy Conservation) | ΔU = q + w. Energy cannot be created or destroyed; it only changes form. | Balances heat and work in reactions; basis for calorimetry. |
| Second | For any spontaneous process, ΔS_total = ΔS_system + ΔS_surroundings > 0. | Predicts directionality; introduces entropy. |
| Third | As T → 0 K, the entropy of a perfect crystal approaches zero. | Provides an absolute entropy reference point. |
First Law (Differential Form)
[
dU = \delta q + \delta w
]
Enthalpy Change at Constant Pressure
[
\Delta H = \Delta U + P\Delta V
]
Entropy Change (Reversible Process)
[
\Delta S = \int_{i}^{f} \frac{\delta q_{\text{rev}}}{T}
]
Gibbs Free Energy
[
\Delta G = \Delta H - T\Delta S
]
Relationship to Equilibrium Constant
[
\Delta G^\circ = -RT\ln K
]
(R = 8.314 J mol⁻¹ K⁻¹, (K\