Solutions (Terminology)

[@komalkumar2474]

one of the best channels for physical chemistry..

[@mortezakhoshbin]

Thanks alot beautiful explanation.. i had an unrelated question if it is possible. i saw the energy needed to break double bond of carbon is about 100 Kcal/mol. what temprature will be sufficient to break this bond?

[@PhysicalChemistry]

It's useful to think about this as a probability... and you can work out the probabilities for yourself. Recall the Boltzmann probability distribution (kzbin.info/www/bejne/Y6WwiGufipWSqtU), which will tell you that the probability that the bond is broken, relative to the probability that it is formed, is P(broken) / P(bonded) = exp(-ΔE / kT) (This assumes that the degeneracy is the same for both cases, which is not true. But it works okay as a rough approximation.) Then use your bond strength ΔE and any temperature you like. For example, at T = 298 K, a 100 kcal/mol bond will be broken with P ≈ 5E-74. So essentially none of the C-C bonds will break at room temperature. Then rephrase the question to ask about the specific situation you're interested in. If you have a mole of bonds, at what temperature would you expect to find a single one of them broken (which might then initiate a radical reaction mechanism)? Or at what temperature would you expect to find 1 in 1000, or 1 in 1 million of them broken (which might correspond to when you would begin to see thermal decomposition)? Note that these rough estimates will depend on the value of ΔE. Your estimate of 100 kcal/mol is a little low for a C=C double bond (although it depends on the compound).

[@mortezakhoshbin]

@@PhysicalChemistry thanks alot for this complete explain. it is so helpfull to me🌹🌹🌹

[@GulzarAhmad-sw1kh]

NaCl melts at high temperature but dissolves in water at room temperature. How these two phenomena are different?

[@PhysicalChemistry]

When a (pure) solid melts, it changes into the (pure) liquid phase. The molecules in the liquid (or ions, in the case of NaCl) are surrounded by other molecules (or ions) of the same substance. When a solid dissolves in a solvent to make a solution, the molecules (or ions) of the solute are surrounded by molecules of the solvent. NaCl can dissolve in water at mild temperatures because the energy cost of separating the ions from each other is paid back in part by favorable interactions with the polar water molecules, and is also compensated by an increase in entropy when the solid disperses in the solution.