Thermodynamics Overview and Concepts

Thermodynamics

• Thermodynamics studies heat, energy transfer, and its effect on physical and chemical properties of substances.
• Outcomes include definitions of thermodynamics, basic terminologies, laws of thermodynamics (0th, 1st, 2nd, and 3rd), entropy and enthalpy, free energy, and applications in pharmaceutical processes.

What is Thermodynamics?

• A diagram shows a galvanic cell with anode and cathode, illustrating electrochemical reactions.
• The chemical reaction HCl(aq) + NaOH(aq) → NaCl(s) + H₂O(l) is used as an example to understand if heat from a reaction can be used to do work.
• Thermodynamics involves the relationships between heat, work, and other forms of energy.

Spontaneous Change

• A spontaneous change occurs without a continuous input of energy from outside the system.
• All chemical processes require activation energy.
• Once a spontaneous process begins, no further input of energy is needed.
• A nonspontaneous change requires a continuous supply of energy from the surroundings.
• If a change is spontaneous in one direction, it is nonspontaneous in the reverse direction.

System vs Surroundings

• A system is the space defined by a fixed mass or region in space.
• Surroundings are everything external to the system.
• The boundary separates the system from the surroundings, it can be real or imaginary and fixed or movable.

Types of Systems

• Open systems exchange both energy and matter with their surroundings (e.g., boiling water in an open pan).
• Closed systems exchange energy but not matter with their surroundings (e.g., boiling water in a closed pan).
• Isolated systems exchange neither energy nor matter with their surroundings (e.g., water in a thermos flask).
• The universe is an isolated system.

Properties of a System

• Any characteristic of a system is its property.
• Intensive properties (e.g., density, temperature, pressure) are independent of the mass of the system.
• Extrinsic properties (e.g., volume, enthalpy, entropy, kinetic energy, potential energy) depend on the mass of the system.
• A property per unit mass is a specific property (e.g., specific volume, specific enthalpy, specific entropy, specific heat capacity).

Classification of Processes

• Quasi-static processes are seemingly, allegedly, or supposedly static processes; they are infinitely slow.
• Non-quasi-static processes are not infinitely slow.
• Reversible processes can be reversed by reversing the direction of the changes, without leaving any effects on the system or surroundings.
• Irreversible processes cannot be reversed in the same way.
• All quasi-static processes are not reversible, but reversible processes are always quasi-static.
• Quasi-static compression and expansion of a gas is a reversible process.

Macroscopic vs Microscopic Analysis

• Macroscopic analysis considers the average molecular behavior, valid when the continuum concept holds (e.g., mean free path is much smaller than system dimensions).
• Microscopic analysis considers individual molecular behaviors, valid when the mean free path of molecules is comparable to system dimensions.

Thermodynamic Equilibrium

• Thermal equilibrium involves equal temperatures with no heat transfer.
• Mechanical equilibrium involves equal forces.
• Chemical equilibrium involves chemical composition not changing with time.
• Phase equilibrium means the mass of each phase remains constant over time.

The Laws of Thermodynamics

• C. P. Snow was a British chemist.
• Zeroth Law: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
• First Law: Energy is conserved. The change in internal energy of a system equals the heat added to the system less the work done.
• Second Law: The entropy or disorder of an isolated system always increases.
• Third Law: A perfect crystal has zero entropy at absolute zero.

First Law:

• Law of conservation matter/ Energy: In an isolated system, the total energy remains constant.
• The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Processes

• Adiabatic: No heat transfer, △E = q - w (expansion: w is positive, compression: w is negative).
• Isothermal: Constant temperature, ΔE = 0 for ideal gasses and q = w.
• Isochoric: Constant volume, w = 0, so ΔE = q.
• Isobaric: Constant pressure.

Enthalpy Change

• △H is the heat gained or lost at constant pressure (qp), a criteria for spontaneity.
• △H < 0: Spontaneous reaction
• △H > 0: Not a spontaneous reaction

Types of Enthalpy Change

• Heat of Formation (△H°f)
• Heat of Fusion (△H°f)
• Heat of Vaporization (△H°vap)
• The enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps.

Specific Heat Capacity

• Heat Capacity: q/△T = constant
• Specific Heat Capacity (c): c=q/(△T×m)
• Molar Heat Capacity (C): C=q/(△T×n)

Zeroth Law of Thermodynamics

• Two systems that are in thermal equilibrium with a third system are in thermal equilibrium with each other.
• It establishes the concept of temperature and heat transfer.

Entropy (Microstate)

• Quantized energy levels (electronic, vibrational, rotational, translational).
• At any time (t), particles are at a specific energy level, moving at a specific speed, vibrating and rotating at specific frequencies.
• Each quantized state of the whole system of molecules is called a microstate.

Entropy

• Boltzmann's entropy equation (S = k ln W): S is the entropy of the system, k is Boltzmann's constant, and W is the number of microstates.
• A system with fewer microstates has lower entropy, and a system with more microstates has higher entropy.
• Phase changes (solid to liquid to gas) and dissolving salts typically increase entropy.
• Chemical reactions producing more particles will typically increase entropy.

Change in Entropy

• △Ssys = Sfinal - Sinitial where S is the entropy of the system.
• ∆S° univ = ∆S° sys + ∆S° surr > 0, for a spontaneous process

Second Law of Thermodynamics

• The entropy (disorder) of an isolated system always increases.
• All real processes occur spontaneously in a direction that increases the entropy of the universe.

Entropy and Gibbs Free Energy

• △Suniv is total change of entropy in the universe.
• If △Suniv > 0, the process is spontaneous; if △Suniv < 0, then the process is non-spontaneous

Standard Entropy of Reaction (△S°rxn)

• △S°rxn is entropy change in standard state conditions, where reactants and products are in standard states.
• Moles of gases: ↑ in gases ↑ in entropy (usually +ve)

Entropy Change and Spontaneous Reactions

• △S° univ must be +ve for a reaction to be spontaneous.

Standard Entropy

• Entropy values can be used to calculate △S°rxn

Calculate △G°

• Given a reaction, you can calculate △G° using enthalpy and entropy values

Gibbs Equation and Gibbs Free Energy

• Gibbs equation (△G = △H - T△S) for calculating free energy.
• At standard state conditions, △G° = -RT lnK, where K is the equilibrium constant

Calculating △AG

• Calculating △AG° from △G°f values (standard free energy of formation): △G° rxn = Σn△Gf° (products) - Σm△Gf° (reactants)

Factors Affecting Entropy

• Temperature: Entropy increases with temperature.
• Physical state: Entropy increases as a substance changes from solid to liquid to gas.
• Solution formation: Entropy increases when a substance dissolves.
• Molecular complexity: Entropy increases with increasing complexity in a molecule.

Effect of Temperature on Reaction Spontaneity

• The sign of △G may change at different temperatures.

Temperature and Reaction Spontaneity

• Finding the temperature at which a reaction becomes spontaneous:
• T = △H / △S

Equilibrium State

• For any process approaching equilibrium, △S° univ is greater than or equal to zero
• When a system reaches equilibrium, no net reaction occurs in either direction

ΔG, Q, and K

• AG = RT ln Q/K, where Q is reaction quotient relative to the reaction's extent and K is the equilibrium constant. This equation gives the change in Gibbs free energy.

ΔG and Equilibrium Constant

Summary Table

Explore the fascinating study of thermodynamics, including its fundamental laws, key terminologies, and the concepts of entropy and enthalpy. Understand the role of thermodynamics in chemical reactions and energy transfer through practical examples. This quiz will help solidify your grasp of both basic and advanced thermodynamic principles.