Gibbs free energy (G) will always be negative for spontaneous processes at constant temperature and pressure, indicating that the reaction can occur without external input. Conversely, Gibbs free energy will be positive for non-spontaneous processes, suggesting that the reaction requires energy input to proceed. When G is zero, the system is at equilibrium, meaning there is no net change in the concentrations of reactants and products.
Gibbs free energy (ΔG) will always be negative for a spontaneous process occurring at constant temperature and pressure. This typically occurs when the change in enthalpy (ΔH) is negative (exothermic reactions) and the change in entropy (ΔS) is positive, leading to a favorable increase in disorder. Additionally, even if ΔH is positive, a sufficiently large positive change in entropy can also result in a negative ΔG at high temperatures, according to the equation ΔG = ΔH - TΔS.
For a reaction with a positive enthalpy change (ΔH > 0) and a positive entropy change (ΔS > 0), the spontaneity is influenced by temperature through the Gibbs free energy equation: ΔG = ΔH - TΔS. As temperature increases, the TΔS term becomes larger, which can make ΔG more negative, thereby favoring spontaneity. Therefore, at higher temperatures, the reaction is more likely to be spontaneous, while at lower temperatures, it may not be spontaneous.
The purpose is to determine the available energy. Some of the energy in any system is useless - can't be converted into useful work.
In a spontaneous reaction, the value of ΔG (Gibbs free energy change) is less than 0. This indicates that the reaction can occur without the input of external energy, favoring the formation of products. If ΔG is greater than 0, the reaction is non-spontaneous, and if ΔG equals 0, the system is at equilibrium. Thus, for spontaneity, ΔG must be negative.
quadski
Since the question seems to be about reactions - and the whole idea of a reaction is that something is changing... The CHANGE in Gibbs free energy will always be positive for a spontaneous reaction. As far as whether the Gibbs free energy of a system (without the term "change" attached) ... Since Gibbs free energy is a state function, it is always defined relative to a standard state. Asking if the Gibbs free energy is positive is akin to asking how "high" something is - the answer depends on where you define zero to be. If you define 0 height to be the level of the ground you are standing on, you will get a different answer than if you define zero height to be "sea level". A cactus in Death Valley may have a positive height relative to the ground, but would actually have a negative height relative to sea level. Likewise, the Gibbs free energy of a system will be positive or negative (or zero) depending on what you define as the standard state.
The Gibbs free energy will always be negative for a spontaneous reaction at constant temperature and pressure. This suggests that the reaction is thermodynamically favorable and can proceed without the input of external energy.
Gibbs free energy (ΔG) will always be negative for a spontaneous process occurring at constant temperature and pressure. This typically occurs when the change in enthalpy (ΔH) is negative (exothermic reactions) and the change in entropy (ΔS) is positive, leading to a favorable increase in disorder. Additionally, even if ΔH is positive, a sufficiently large positive change in entropy can also result in a negative ΔG at high temperatures, according to the equation ΔG = ΔH - TΔS.
Since the question seems to be about reactions - and the whole idea of a reaction is that something is changing... The CHANGE in Gibbs free energy will always be positive for a spontaneous reaction. As far as whether the Gibbs free energy of a system (without the term "change" attached) ... Since Gibbs free energy is a state function, it is always defined relative to a standard state. Asking if the Gibbs free energy is positive is akin to asking how "high" something is - the answer depends on where you define zero to be. If you define 0 height to be the level of the ground you are standing on, you will get a different answer than if you define zero height to be "sea level". A cactus in Death Valley may have a positive height relative to the ground, but would actually have a negative height relative to sea level. Likewise, the Gibbs free energy of a system will be positive or negative (or zero) depending on what you define as the standard state.
when H is negative and S is positive
Gibbs energy accounts for both enthalpy (heat) and entropy (disorder) in a system. A reaction will be spontaneous if the Gibbs energy change is negative, which occurs when enthalpy is negative (exothermic) and/or entropy is positive (increased disorder). The relationship between Gibbs energy, enthalpy, and entropy is described by the equation ΔG = ΔH - TΔS, where T is temperature in Kelvin.
The units of Gibbs energy are joules (J) or kilojoules (kJ). Gibbs energy is related to the thermodynamic properties of a system by indicating whether a process is spontaneous or non-spontaneous. If the Gibbs energy is negative, the process is spontaneous, and if it is positive, the process is non-spontaneous.
When H is positive and S is negative
Photosynthesis is a positive delta G as it produces more free energy than it uses. The overall result of the Gibbs equations shows that delta G is positive
The name of the single thermodynamic quantity is Gibbs free energy (G). The symbol for Gibbs free energy is ΔG (delta G). The sign of ΔG determines whether a reaction is spontaneous (negative ΔG) or non-spontaneous (positive ΔG).
The units of Gibbs free energy are joules (J) or kilojoules (kJ). Gibbs free energy is a measure of the energy available to do work in a system at constant temperature and pressure. It relates to the thermodynamic properties of a system by indicating whether a reaction is spontaneous (negative G) or non-spontaneous (positive G) under given conditions.
The Gibbs energy formula is G H - TS, where G is the change in Gibbs energy, H is the change in enthalpy, T is the temperature in Kelvin, and S is the change in entropy. This formula is used to determine if a chemical reaction is thermodynamically feasible by comparing the change in Gibbs energy to zero. If G is negative, the reaction is spontaneous and feasible. If G is positive, the reaction is non-spontaneous and not feasible.