ΔG, or Gibbs free energy change, measures whether a process is thermodynamically spontaneous in Intro to Chemistry. A negative ΔG means the process can happen on its own under the given conditions.
ΔG is Gibbs free energy change, and in Intro to Chemistry it tells you whether a process is thermodynamically favorable under a given set of conditions. If ΔG is negative, the process can proceed spontaneously. If ΔG is positive, the process is nonspontaneous and needs continuous outside energy input to keep going.
The shortcut chemistry uses most often is ΔG = ΔH - TΔS. That equation shows that spontaneity is not based on heat alone. ΔH is the enthalpy change, T is the temperature in Kelvin, and ΔS is the entropy change. A process can be helped by releasing heat, by increasing disorder, or by both. Temperature matters because the TΔS term gets bigger at higher temperatures.
That is why some processes change behavior with temperature. A reaction that looks unfavorable at one temperature may become favorable at another if the entropy term starts to win. This is a big idea in basic thermodynamics, because it shows that spontaneity is a balance between energy and dispersal, not just whether something is "energetic" or "lazy."
In solution chemistry, ΔG shows up when you ask whether a solute will dissolve. Dissolution often involves breaking apart the solute, separating solvent particles, and forming new solute-solvent attractions. If the overall enthalpy and entropy changes make ΔG negative, the substance dissolves more readily. If not, the solute may stay mostly undissolved.
At equilibrium, ΔG = 0. That means the forward and reverse processes are balanced, so there is no net change over time. A lot of Intro to Chemistry problems ask you to sort a process into spontaneous, nonspontaneous, or at equilibrium based on the sign of ΔG, or to use the equation to predict how a temperature change shifts the outcome.
ΔG shows up any time you need to predict whether a chemical process will happen without constant outside energy. In Intro to Chemistry, that makes it one of the main tools for connecting thermodynamics to real reactions, phase changes, and dissolving substances.
It also gives you a way to connect three ideas that are often taught separately: enthalpy, entropy, and temperature. Instead of treating heat and disorder as unrelated facts, you can use ΔG to see how they work together. That is especially useful when a problem asks why a process is spontaneous even though it absorbs heat, or why a process changes behavior when the temperature changes.
For dissolution, ΔG helps explain why some ionic or molecular compounds dissolve easily in water while others barely dissolve. The issue is not just "does it like water?" The question is whether the overall process lowers free energy enough for the dissolved state to be favored.
ΔG also connects to equilibrium. When a system reaches equilibrium, there is no net driving force for change, so ΔG is zero. That gives you a clean way to interpret what equilibrium means at the particle level: the system is not frozen, but the forward and reverse changes are balanced.
If you are writing lab conclusions, working through thermodynamics problems, or explaining why a process proceeds one way and not another, ΔG is usually the term that turns your observation into a chemistry explanation.
Keep studying Intro to Chemistry Unit 16
Visual cheatsheet
view galleryEnthalpy (ΔH)
ΔH tells you whether a process absorbs or releases heat, but it does not decide spontaneity by itself. In the ΔG equation, a negative ΔH often favors a negative ΔG, especially when entropy does not fight against it. In Intro to Chemistry problems, you usually look at ΔH first, then check how the entropy term changes the result.
Entropy (ΔS)
ΔS measures how much the energy or particles spread out in a process. A positive ΔS often pushes ΔG lower because the term TΔS is subtracted in the Gibbs equation. That is why dissolving, mixing, and gas-forming processes often become more favorable when disorder increases.
Equilibrium
Equilibrium is the point where the forward and reverse processes occur at the same rate, so there is no net change. For Gibbs free energy, that means ΔG = 0. When you see an equilibrium question in Intro to Chemistry, ΔG helps you tell whether the system still has a driving force to change.
ΔHsoln
ΔHsoln is the enthalpy change for dissolving a solute in a solvent. It is one piece of the free-energy picture for solutions, but not the whole story. A solute can have an unfavorable ΔHsoln and still dissolve if the entropy change is large enough to make ΔG negative.
A problem set question may give you ΔH, ΔS, and a temperature, then ask you to calculate ΔG and decide whether the process is spontaneous. You might also see a conceptual item asking why a substance dissolves better at one temperature than another. The move is to use the sign of ΔG, not just memorize the formula. If ΔG is negative, the process is thermodynamically favored; if it is positive, it is not spontaneous under those conditions. If ΔG equals zero, you are at equilibrium. In lab writeups and short answers, you may need to explain a dissolution or reaction result by linking heat, disorder, and temperature instead of giving only one of them.
ΔH is only the heat change at constant pressure, while ΔG combines enthalpy with entropy and temperature to predict spontaneity. A process can be endothermic and still have a negative ΔG if the entropy term is large enough. If you mix them up, you may wrongly decide that heat absorption always means a process will not happen.
ΔG is Gibbs free energy change, and it tells you whether a process is spontaneous under specific conditions.
A negative ΔG means the process can happen on its own, a positive ΔG means it is nonspontaneous, and ΔG = 0 means equilibrium.
The equation ΔG = ΔH - TΔS shows that heat, entropy, and temperature all affect spontaneity.
In Intro to Chemistry, ΔG comes up often in dissolution, reaction prediction, and thermodynamics questions.
Do not judge spontaneity from enthalpy alone, because entropy and temperature can change the outcome.
ΔG is Gibbs free energy change, a thermodynamic value used to predict whether a process is spontaneous. In Intro to Chemistry, it combines enthalpy, entropy, and temperature into one number. Negative ΔG means the process is favored under those conditions.
If ΔG is less than zero, the process is spontaneous. If ΔG is greater than zero, it is nonspontaneous and needs outside energy input. If ΔG equals zero, the system is at equilibrium.
ΔH measures heat change at constant pressure, while ΔG tells you whether a process will happen on its own. A reaction can absorb heat and still be spontaneous if the entropy term makes ΔG negative. That is why ΔG is the better predictor for spontaneity.
Temperature changes the size of the TΔS term in the equation ΔG = ΔH - TΔS. At higher temperatures, entropy has more influence on the result. That is why some processes become spontaneous only when the temperature rises.