16.1 Spontaneity
2 min read•june 25, 2024
in chemistry is all about processes that happen naturally without outside help. Think of ice melting at room temp or gas spreading out. These processes increase disorder and spread out matter and energy.
is the key to predicting spontaneity. It combines heat content, temperature, and entropy. If the change in Gibbs is negative, the process happens on its own. Temperature, heat release, and increased disorder all play a role.
Spontaneity and Gibbs Free Energy
Spontaneous vs nonspontaneous processes
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- occur naturally without external intervention (ice melting at room temperature, gas expanding to fill a container, iron rusting in the presence of oxygen and water)
- require external energy input to occur (water freezing at room temperature, gas being compressed into a smaller volume, rust being converted back into pure iron)
Dispersion in spontaneous processes
- Entropy () measures the disorder or randomness of a system
- Spontaneous processes involve an increase in entropy of the universe (), which includes both the system and its surroundings
- Matter becomes more dispersed during spontaneous processes
- Gas molecules spread out to fill a container
- Solute dissolves in a solvent
- Energy spreads out and becomes less concentrated during spontaneous processes
- Heat flows from a hot object to a cold object
- A concentrated solution becomes more dilute over time
Gibbs free energy for spontaneity
- Gibbs free energy () predicts the spontaneity of a process at constant temperature and pressure
- Defined as:
- represents enthalpy (heat content)
- represents absolute temperature (in )
- represents entropy
- Defined as:
- The change in Gibbs free energy () determines the spontaneity of a process using the equation
- If , the process is spontaneous
- If , the process is nonspontaneous
- If , the process is at equilibrium (no net change)
- Factors affecting :
- Higher temperatures favor processes with positive (entropy-driven)
- processes () are favored
- Processes with increased disorder () are favored
Thermodynamics and Spontaneity
- is the study of energy transfer and its relationship to spontaneous processes
- The states that the entropy of the universe always increases for spontaneous processes
- Free energy is a measure of the maximum useful work that can be extracted from a system (Gibbs free energy)
- is the change in free energy when the amount of a substance in a system changes
- in thermodynamics refers to processes that can be reversed without any net change in the system or surroundings
Key Terms to Review (27)
$ ext{Delta S}_{ ext{universe}}$: $ ext{Delta S}_{ ext{universe}}$ refers to the change in entropy of the entire universe during a spontaneous process. Entropy is a measure of the disorder or randomness of a system, and the second law of thermodynamics states that the entropy of the universe always increases for a spontaneous process.
$
Delta H$: $
Delta H$ is the change in enthalpy, a thermodynamic property that represents the total energy released or absorbed during a chemical process or physical transformation at constant pressure. It is a measure of the heat energy exchanged between a system and its surroundings, and is a crucial concept in understanding chemical reactions, phase changes, and spontaneity of processes.
$\Delta G$: $\Delta G$, or Gibbs free energy change, is a thermodynamic quantity that measures the maximum reversible work that can be performed by a system at constant temperature and pressure. It helps determine whether a reaction will occur spontaneously; if $\Delta G$ is negative, the reaction can happen without external input, while a positive $\Delta G$ indicates that energy must be added for the process to occur. Understanding $\Delta G$ is crucial for predicting the behavior of chemical processes, especially during dissolution and assessing spontaneity.
$\Delta S$: $\Delta S$, or the change in entropy, refers to the measure of disorder or randomness in a system during a process. It indicates how the distribution of energy changes within a system, impacting the spontaneity of processes. When a system undergoes a change, such as dissolving a solute or a reaction, the value of $\Delta S$ can help predict whether that change is likely to occur naturally, highlighting the balance between energy dispersal and organization.
$G$: $G$ is a thermodynamic quantity that represents the free energy of a system, which is the maximum amount of work that can be extracted from the system under constant temperature and pressure conditions. It is a crucial concept in understanding the spontaneity and feasibility of chemical reactions and processes.
$H$: $H$ is a thermodynamic variable that represents the total energy content of a system, including both the internal energy and the work done on or by the system. It is a crucial concept in the study of spontaneous processes and the direction of energy flow in chemical and physical systems.
$S$: $S$ is a key term that represents the spontaneity of a process or reaction. Spontaneity refers to the natural tendency of a system to undergo a change or transformation without the input of external energy. This concept is central to understanding the thermodynamics of chemical and physical processes.
$T$: $T$ is a fundamental concept in thermodynamics that describes the degree of disorder or randomness in a system. It is a measure of the amount of energy in a system that is not available to do useful work, but is instead dissipated as heat. $T$ is a crucial factor in determining the spontaneity and direction of chemical and physical processes.
Chemical Potential: Chemical potential is a measure of the tendency of a chemical species to escape from a given phase and participate in a chemical reaction. It represents the amount of energy that a substance has due to its chemical composition and physical state, which determines its reactivity and ability to undergo spontaneous changes.
Chemical thermodynamics: Chemical thermodynamics studies the interrelation of heat and work with chemical reactions or physical changes. It applies principles of thermodynamics to predict the direction and extent of chemical processes.
Dispersion: Dispersion is the separation of a substance into its constituent parts or elements, often in the context of light or other forms of electromagnetic radiation. It is a fundamental concept that underpins various phenomena in chemistry, physics, and other scientific disciplines.
Exothermic: Exothermic refers to a chemical reaction or process that releases energy in the form of heat to the surrounding environment. These reactions produce more energy than they consume, resulting in a net release of heat.
Exothermic process: An exothermic process is a chemical reaction or physical change that releases heat to its surroundings. This release of energy usually results in an increase in the temperature of the surroundings.
Free Energy: Free energy is a thermodynamic concept that represents the maximum amount of work that can be extracted from a system while maintaining a constant temperature and pressure. It is a measure of the energy available to do useful work and is a crucial factor in determining the spontaneity and feasibility of chemical reactions and physical processes.
Free energy change (ΔG): Free energy change ($\Delta G$) is the difference in free energy between the products and reactants in a chemical reaction. It determines whether a process is spontaneous or non-spontaneous.
Gibbs Free Energy: Gibbs free energy is a thermodynamic property that combines the concepts of enthalpy and entropy to determine the spontaneity and feasibility of a chemical process. It is a crucial factor in understanding the driving forces behind chemical reactions and phase changes.
Gibbs free energy (G): Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure. It is used to predict the direction of chemical reactions.
Kelvin: Kelvin is the base unit of temperature in the International System of Units (SI). It is named after the physicist William Thomson, also known as Lord Kelvin, who was the first to propose an absolute scale of temperature. The Kelvin scale is a fundamental quantity in various areas of chemistry, including measurements, the ideal gas law, collision theory, and the study of spontaneity.
Kelvin (K): Kelvin (K) is the SI unit of thermodynamic temperature. It is one of the seven base units in the International System of Units (SI).
Nonspontaneous Processes: Nonspontaneous processes are physical or chemical changes that do not occur naturally or on their own without the input of external energy. These processes require an energy source or external work to be performed in order to proceed, unlike spontaneous processes which occur naturally and without any energy input.
Reversibility: Reversibility refers to the ability of a process or reaction to be reversed, meaning it can proceed in both the forward and backward directions. This concept is particularly important in the context of spontaneity and free energy, as it determines the direction and feasibility of a given process.
Second law of thermodynamics: The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. It implies that natural processes increase the overall disorder or randomness of a system.
Second Law of Thermodynamics: The second law of thermodynamics states that the total entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium. It is a fundamental principle that describes the direction of spontaneous processes in the universe.
Spontaneity: Spontaneity refers to the inherent tendency of a system or process to occur naturally, without the need for external intervention or energy input. It is a fundamental concept in chemistry that describes the natural, unforced progression of a reaction or physical change towards a more stable or favorable state.
Spontaneous process: A spontaneous process is a physical or chemical change that occurs without external intervention. It is driven by a decrease in free energy and an increase in entropy.
Spontaneous Processes: Spontaneous processes are natural, self-driven changes that occur in a system without the need for external energy input. They are characterized by an increase in the disorder or randomness of the system, as described by the Second Law of Thermodynamics.
Thermodynamics: Thermodynamics is the branch of physics that deals with the relationships between heat, work, temperature, and energy. It describes the fundamental physical laws governing the transformation of energy and the flow of heat, which are essential to understanding the behavior of chemical systems and processes.