# Tag Info

## Hot answers tagged physical-chemistry

8

(This might get more/better answers on Physics Stack Exchange) At the high temperatures of the early Big Bang, you have individual protons and electrons, not hydrogen atoms and molecules. This is because the $kT$ thermal energy is much, much more than the binding energy of the hydrogen atom. In that case, the moving individual charges create a continuous ...

7

It sounds like your confusion arises from not making a distinction between $\Delta G$ and $\Delta G^\circ$ when describing a reaction as spontaneous or not. The $\Delta G^\circ$ is the free energy change for the reaction at the defined "standard" conditions of 1 M solute concentrations and/or 1 bar gas partial pressures of both the reactants and products. ...

7

The $\sigma_\mathrm v$ mirror planes in the $C_\mathrm{3v}$ point group are themselves related by symmetry: note that they can be interchanged via rotation by 120 degrees about the preexisting $C_3$ axis. To be technically precise, they belong to the same conjugacy class, in the sense that applying $C_3$, then one mirror plane, and then the inverse of $C_3$ ...

4

In general it is necessary to consider any entropy changes in determining whether a system is at equilibrium or if a spontaneous change will occur. As there must be an increase in entropy in actual processes then $dS_{system}+dS_{surr}=dS_{irrev} \ge 0$. By using the first law with the last expression and after several steps, we find that in an ...

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An indicator does not affect a particular reaction. But in your solution, you have two successive reactions when adding HCl to this solution : First $$\ce{CO_3^{2-} + H^+ -> HCO_3^-}$$ and a given indicator must be added to determine the end of this reaction. If you don't, all you see is a colorless solution being transformed into another colorless ...

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I agree with Andrew that it depends on whether you define spontaneity based on $\Delta G^\circ <0$ or $\Delta G < 0$. Typically, freshman chemistry books use the former. However, I've never liked equating spontaneity with the sign of $\Delta G^\circ$, prefering to instead use the sign of $\Delta G^\circ$ as an indicator of whether reactants or ...

1

First, not all gases can be liquefied at room temperature by increasing pressure. If the gas is above the critical temperature, it cannot be liquefied by any increase in pressure; it becomes a supercritical fluid. Supercritical fluids have some of the properties of a gas (e.g. diffusing through fine openings), ans some of liquids (e.g. dissolving solids and ...

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Here is a simple example that may help from application of the Rault's Law (see this video), where colligative properties of a solution mixes apply (linearly or with deviations) to the relative molar concentration of solute compositions and not the identity of the solute. First, take a known amount of CaCl2 and place it into a known volume of water, but do ...

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Roughly (in the ideal world), colligative properties depend on the number concentration of particles, not on what those particles are. A particle can be a micelle or vesicle or other colloidal particle such as a polymer, or a nonassociated solute molecule. For instance, a protein is a polymer usually consisting of a linear chain of aminoacids. It is ...

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This question shows that you have probably not really understood what the free enthalpy (or Gibbs energy, or free energy) is. I will try to explain it qualitatively without too much thermodynamics. Let's go ! The origin of the Gibbs energy is coming from Gibbs' reflexions on the spontaneity of chemical reactions. He was trying to find a potential energy ...

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