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When ΔS > 0 and ΔH < 0, the process is always spontaneous as written. When ΔS < 0 and ΔH > 0, the process is never spontaneous, but the reverse process is always spontaneous. When ΔS > 0 and ΔH > 0, the process will be spontaneous at high temperatures and non-spontaneous at low temperatures. When ΔS < 0 and ΔH < 0, the process will be ...
Spontaneous emission is the process in which a quantum mechanical system (such as a molecule, an atom or a subatomic particle) transits from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantized amount of energy in the form of a photon. Spontaneous emission is ultimately responsible for most of the light ...
The T-V diagram of the rubber band experiment. The decrease in the temperature of the rubber band in a spontaneous process at ambient temperature can be explained using the Helmholtz free energy = where dF is the change in free energy, dL is the change in length, τ is the tension, dT is the change in temperature and S is the entropy.
or dG < 0. For a similar process at constant temperature and volume, the change in Helmholtz free energy must be negative, <. Thus, a negative value of the change in free energy (G or A) is a necessary condition for a process to be spontaneous. This is the most useful form of the second law of thermodynamics in chemistry, where free-energy ...
For a process at constant temperature and pressure without non-PV work, this inequality transforms into <. Similarly, for a process at constant temperature and volume, <. Thus, a negative value of the change in free energy is a necessary condition for a process to be spontaneous; this is the most useful form of the second law of thermodynamics ...
Some of the largest volcanic eruptions on the planet have occurred at Yellowstone National Park, and scientists have determined when the next one could occur.
Note that this simple theory predicts that this contribution to the diffusiophoretic motion is always up a salt concentration gradient, it always moves particles towards higher salt concentration. By contrast, the sign of the electric-field contribution to diffusiophoresis depends on the sign of β ζ {\displaystyle \beta \zeta } .
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