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.
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.
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.
An endergonic reaction is a reaction in which the change in Gibbs free energy is positive, indicating that the reaction requires an input of energy to proceed. This means that the products of the reaction have more free energy than the reactants.
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 and standard free energy are both measures of the energy available to do work in a chemical reaction. The main difference is that Gibbs free energy takes into account the temperature and pressure of the system, while standard free energy is measured under specific standard conditions. In chemical reactions, the change in Gibbs free energy determines whether a reaction is spontaneous or non-spontaneous. If the Gibbs free energy change is negative, the reaction is spontaneous, while a positive change indicates a non-spontaneous reaction. The relationship between Gibbs free energy and standard free energy lies in the fact that the standard free energy change can be used to calculate the Gibbs free energy change under any conditions.
when H is negative and S is positive
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.
When H is positive and S is negative
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 Gibbs free energy is a measure of the energy available to do work in a system. When the Gibbs free energy is lower, the system is more stable because it has less tendency to change or react with its surroundings. In other words, a lower Gibbs free energy indicates a more stable system.
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 units for Gibbs free energy are joules (J) in the International System of Units (SI).