Free energy

Definition

Free energy is the amount of work a system can perform at constant temperature and pressure. It represents the energy available to do work, factoring in both the internal energy of the system and its entropy. Understanding free energy is crucial because it helps to determine the spontaneity of reactions and processes in biological systems.

5 Must Know Facts For Your Next Test

1. Free energy is calculated using the equation: $$ G = H - TS $$, where G is Gibbs free energy, H is enthalpy, T is temperature in Kelvin, and S is entropy.
2. A negative change in free energy ($$ \\Delta G < 0 $$) indicates that a reaction or process can occur spontaneously, while a positive change ($$ \\Delta G > 0 $$) means it is non-spontaneous.
3. Biological reactions often require a net release of free energy to proceed, making the concept vital for understanding metabolism and energy transformations.
4. The concept of free energy helps to explain why certain reactions, despite being exothermic (releasing heat), may not occur if they lead to an increase in disorder that outweighs the energy released.
5. In living organisms, free energy drives processes such as cellular respiration and photosynthesis, allowing cells to perform work necessary for life.

Review Questions

• How does free energy relate to the spontaneity of biochemical reactions?
  • Free energy is key to understanding whether biochemical reactions can occur spontaneously. When the change in Gibbs free energy ($$ \\Delta G $$) for a reaction is negative, it indicates that the reaction can happen without the input of additional energy. This relationship allows us to predict which reactions will proceed under biological conditions and which will require external energy input.
• In what ways do enthalpy and entropy contribute to changes in free energy during metabolic processes?
  • Enthalpy and entropy both play crucial roles in determining changes in free energy during metabolic processes. Enthalpy reflects the total heat content and energy changes during reactions, while entropy measures disorder within the system. The relationship among these factors is captured in the Gibbs free energy equation: $$ G = H - TS $$, where an increase in entropy or a decrease in enthalpy can lead to a more negative free energy change, promoting spontaneity in reactions.
• Evaluate the importance of understanding free energy in the context of cellular respiration and photosynthesis.
  • Understanding free energy is essential for analyzing cellular respiration and photosynthesis because it helps explain how organisms convert nutrients into usable energy. In cellular respiration, the breakdown of glucose releases free energy that cells harness for work. Conversely, photosynthesis captures light energy, storing it as chemical potential through changes in free energy. Both processes demonstrate how life relies on managing and transforming free energy to sustain metabolic functions.

Related terms

enthalpy: Enthalpy is the total heat content of a system, used to measure the energy change during chemical reactions, especially at constant pressure.

entropy: Entropy is a measure of disorder or randomness in a system, indicating how much energy in a system is unavailable to do work.

Gibbs free energy: Gibbs free energy is a specific type of free energy that indicates whether a process will occur spontaneously at constant temperature and pressure.