Free Energy

Definition

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.

5 Must Know Facts For Your Next Test

1. The change in free energy, $\Delta G$, determines the spontaneity of a process: if $\Delta G < 0$, the process is spontaneous; if $\Delta G > 0$, the process is non-spontaneous.
2. Free energy is the sum of the system's internal energy ($U$), the work done by the system on its surroundings ($-PV$), and the energy associated with the system's entropy ($-TS$).
3. Processes that decrease the free energy of a system are favored, as they represent a decrease in the system's potential to do useful work.
4. The change in free energy is related to the change in enthalpy ($\Delta H$) and the change in entropy ($\Delta S$) through the equation: $\Delta G = \Delta H - T\Delta S$.
5. At constant temperature and pressure, a system will spontaneously move towards a state of lower free energy, as this represents a more stable and favorable configuration.

Review Questions

• Explain how the concept of free energy relates to the spontaneity of a process.
  • The spontaneity of a process is determined by the change in free energy, $\Delta G$. If $\Delta G < 0$, the process is spontaneous and will occur naturally, as it represents a decrease in the system's free energy and a more stable configuration. Conversely, if $\Delta G > 0$, the process is non-spontaneous and will not occur without the input of external energy. The spontaneity of a process is therefore directly linked to the system's tendency to minimize its free energy.
• Describe the relationship between free energy, entropy, and enthalpy, and how this relationship affects the spontaneity of a process.
  • The change in free energy, $\Delta G$, is related to the change in enthalpy, $\Delta H$, and the change in entropy, $\Delta S$, through the equation: $\Delta G = \Delta H - T\Delta S$. Enthalpy represents the system's internal energy, while entropy represents the system's disorder or randomness. Processes that decrease the free energy of a system are favored, as they represent a decrease in the system's potential to do useful work. This means that processes that have a negative $\Delta H$ (exothermic) and a positive $\Delta S$ (increase in disorder) are more likely to be spontaneous, as they will result in a decrease in the system's free energy.
• Analyze how the concept of free energy can be used to predict and explain the feasibility of chemical reactions and physical processes.
  • The concept of free energy is a powerful tool for predicting and explaining the feasibility of chemical reactions and physical processes. By calculating the change in free energy, $\Delta G$, for a given process, we can determine whether the process is spontaneous and likely to occur naturally ($\Delta G < 0$) or non-spontaneous and requiring the input of external energy ($\Delta G > 0$). This information can be used to guide the design and optimization of chemical processes, as well as to understand the driving forces behind natural phenomena. Additionally, the relationship between free energy, entropy, and enthalpy allows us to analyze the underlying thermodynamic factors that contribute to the spontaneity and feasibility of a process, providing valuable insights into the fundamental principles governing the behavior of chemical and physical systems.

Related terms

Gibbs Free Energy: A measure of the maximum amount of non-expansion work that can be extracted from a closed system at constant temperature and pressure.

Entropy: A measure of the disorder or randomness of a system, which is related to the number of possible microscopic arrangements of the system's particles.

Spontaneity: The tendency of a process to occur naturally without the input of external energy, driven by the system's tendency to minimize its free energy.