05. MG2112 Termodinamika Metalurgi (S01: Kesetimbangan, Energi Bebas Gibbs, Potensial Kimia)

Summary

This lecture explores the fundamental concepts of thermodynamics, focusing on equilibrium systems and the relationship between Gibbs free energy and chemical potential. It covers the concept of stable equilibrium where no further changes occur over time, illustrated by examples like the phase change of water and ice at 0°C. The video delves into reversible processes, potential energy, and the spontaneity of reactions based on changes in Gibbs free energy and chemical potential. The key takeaway is that spontaneous processes occur when the chemical potential of the system decreases, enabling work to be done without external input.

Takeaways

• 😀 Equilibrium is a fundamental concept in thermodynamics, referring to a system's state where there is no change over time, meaning the system is stable and not undergoing any transformations.
• 😀 In thermodynamics, equilibrium is typically marked by uniform temperature across all phases, though the system may consist of multiple phases that are still in balance.
• 😀 An example of equilibrium is the coexistence of liquid water and ice at 0°C and 1 ATM pressure, where the two phases (solid and liquid) are stable and in equilibrium.
• 😀 A system is considered to be at equilibrium if no net work is done on or by the system, and no changes are observed in energy or phases over time.
• 😀 The concept of reversible work is crucial in understanding equilibrium; when reversible work is zero, the system is in a state of equilibrium and cannot do further work.
• 😀 Gibbs free energy (G) plays a central role in determining whether a process will occur spontaneously. If ΔG is negative, the process is spontaneous; if positive, it requires external work.
• 😀 The chemical potential of a substance reflects its potential to change, and the system reaches equilibrium when the chemical potentials of all components are equal.
• 😀 When considering a system in equilibrium, its energy (both potential and kinetic) is balanced, meaning that no energy is being transferred in or out of the system, and thus no work can be done.
• 😀 Spontaneous processes occur when the chemical potential of the system decreases, analogous to how water flows from a higher to a lower potential (like a waterfall).
• 😀 The equilibrium condition can be described by the equation ΔG = 0, where the system is stable, with no net change in energy or phase between the components.
• 😀 The laws of thermodynamics, particularly the first and second laws, are essential in understanding how systems behave at equilibrium, emphasizing energy conservation and entropy considerations.

Q & A

What is the concept of equilibrium in thermodynamics?

Equilibrium in thermodynamics refers to a state where a system's properties remain constant over time, meaning no changes occur with respect to time. This state is stable, with uniform temperature, but can have phases that are not homogeneous, like the coexistence of liquid water and ice at 0°C.

How is thermodynamic equilibrium related to temperature and phase changes?

Thermodynamic equilibrium is achieved when the temperature is uniform across the system, and there is no phase transition occurring within the system. For example, at 0°C and 1 ATM pressure, water and ice can exist in equilibrium, with no further changes unless external conditions like temperature or pressure change.

What does 'reversible work' mean in the context of equilibrium?

Reversible work refers to work that can be done by a system in equilibrium, where no energy is lost to the surroundings. In equilibrium, the system can no longer perform any reversible work, as the system's energy is balanced and stable, meaning no net energy is available to perform work.

What is Gibbs free energy and how does it relate to equilibrium?

Gibbs free energy (G) is a thermodynamic potential that measures the useful work obtainable from a system at constant temperature and pressure. At equilibrium, the change in Gibbs free energy (ΔG) equals zero, indicating that the system can no longer do work and is in a stable state.

What does the relationship between Gibbs free energy and chemical potential tell us about equilibrium?

The chemical potential (μ) is related to the Gibbs free energy in that when the chemical potentials of the components in the system are equal, the system is in equilibrium. If the chemical potential of one component is higher than that of another, the system will move toward equilibrium by transferring the substance from high to low chemical potential.

How does the first law of thermodynamics apply to equilibrium?

The first law of thermodynamics, which states that energy cannot be created or destroyed, applies to equilibrium in that during a reversible process, the internal energy of the system remains constant. At equilibrium, the system is in a stable energy state where no further energy transformation occurs.

What role does entropy play in the concept of equilibrium?

Entropy is a measure of disorder or randomness in a system. At equilibrium, the entropy of the system reaches a maximum, meaning the system has reached its most probable and stable state. Any reversible process will move towards increasing entropy, which aligns with the second law of thermodynamics.

Why is spontaneous change in thermodynamics associated with negative Gibbs free energy?

A negative change in Gibbs free energy (ΔG < 0) indicates that a process is spontaneous, meaning it can occur without external input. This corresponds to a decrease in the system's energy, where energy is released to the surroundings, often in the form of work or heat.

How does the concept of equilibrium relate to phase transitions like melting and freezing?

In phase transitions like melting or freezing, equilibrium is achieved when the rates of the forward and reverse processes are equal. For example, at 0°C, liquid water and ice can coexist in equilibrium, meaning the rate of ice melting equals the rate of water freezing under specific temperature and pressure conditions.

What is the significance of the equation ΔG = ΔH - TΔS in thermodynamics?

The equation ΔG = ΔH - TΔS relates Gibbs free energy (ΔG) to enthalpy (ΔH) and entropy (ΔS). It shows that a process is spontaneous when ΔG is negative, which occurs when the enthalpy change (ΔH) is negative (energy is released) and/or the entropy change (ΔS) is positive (disorder increases).