We went over to Penarth, which I believe has been a filming location and from there you can see Flat Holm Island, another ratehr fabulous location.
Now I get to eat more of yesterday's apple crumble and get started on an essay that I don't want to be doing last minute on Wednesday night like last month... (which despite not having time to put a conclusion in, I got 73% for). Ad astra per aspera
Yes, it's nerd Sunday! In the end, might makes right. Nothing has changed since the caveman.
My phys chem textbook has been borrowed by a friend but let's see...
By having impurities in the solvent, it alters the energy of the system. Depending on what the impurity is, the electrostatic forces between water-impurity are different to the forces between water-water. Also, by adding an impurity, you've effectively diluted the solvent.
With sea salt, the presence of Na+ and Cl- causes a restructuring of the alignment of water molecules in order to keep the charges dispersed and dissolved in solution. But salt isn't dissolved in the solid state. Therefore the chemical potential of the solvent in the solid state is unchanged. But the chemical potential of the solvent in liquid state is changed.
Chemical potential is to do with the energy of the system. The freezing point occurs when the energy of the solid state is in equilibrium to that of the liquid state and this is temperature dependent. If you change the chemical potential or energy of the system by introducing impurities, you change the point at which that equilibrium between solid and liquid state occurs.
The freezing point drops because the new chemical potential of the impure solvent in liquid state needs to find the new equilibrium point with the solid state solvent, and this is occurs at a lower temperature. Ad astra per aspera
Can you give me a layman's view of what it means? Never got it straight in college/grad school and ain't doing much better now.
Thank You. In the end, might makes right. Nothing has changed since the caveman.
In this case the claim is that the chemical potential between water ice and pure water is higher than the chemical potential between water ice and water with a solute. The chemical potential depends on the concentration of the solute.
The chemical potential difference between pure water and water with a solute is proportional to the osmotic pressure across a semipermeable membrane separating pure water from water with a solute. En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma
Is that it? In the end, might makes right. Nothing has changed since the caveman.
If you have to "buy" #2 but you "get" osmotic pressure"...
How do you explain osmotic pressure in layman terms in a way that doesn't make it easy to see that it is proportional to the energy difference per water molecule between two phases with differenc solute concentrations?
The energy per molecule is by definition the chemical potential. En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma
In the wikipedia article on freezing point depression it says
The freezing point depression is a colligative property, which means that it is dependent on the presence of dissolved particles and their number, but not their identity. It is an effect of the dilution of the solvent in the presence of a solute. It is a phenomenon that happens for all solutes in all solutions, even in ideal solutions, and does not depend on any specific solute-solvent interactions. The freezing point depression happens both when the solute is an electrolyte, such as various salts, and a nonelectrolyte. In thermodynamic terms, the origin of the freezing point depression is entropic and is most easily explained in terms of the chemical potential of the solvent.
A related notion, osmotic potential is the opposite of water potential, is the degree to which a solvent tends to stay in a liquid.
the potential energy of water relative to pure free water (e.g. deionized water) in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects including surface tension. Water potential is measured in units of pressure and is commonly represented by the Greek letter Ψ (Psi). This concept has proved especially useful in understanding water movement within plants, animals, and soil. Typically, pure water with standard temperature and pressure (or other suitable reference condition) is defined as having a water potential of 0. The addition of solutes to water lowers its potential (makes it more negative), just as the increase in pressure increases its potential (makes it more positive). If possible, water will move from an area of higher water potential to an area that has a lower water potential. One very common example is water that contains a dissolved salt, like sea water or the solution within living cells. These solutions typically have negative water potentials, relative to the pure water reference. If there is no restriction on flow, water molecules will proceed from the locus of pure water to the more negative water potential of the solution.
lowering of vapor pressure; elevation of boiling point; depression of freezing point and osmotic pressure.
Chemical potential energy is a form of potential energy related to the structural arrangement of atoms or molecules. This arrangement may be the result of chemical bonds within a molecule or otherwise. Chemical energy of a chemical substance can be transformed to other forms of energy by a chemical reaction. As an example, when a fuel is burned the chemical energy is converted to heat, same is the case with digestion of food metabolized in a biological organism. Green plants transform solar energy to chemical energy through the process known as photosynthesis, and electrical energy can be converted to chemical energy through electrochemical reactions. The similar term chemical potential is used by chemists to indicate the potential of a substance to undergo a chemical reaction.
Chemical potential energy is a form of potential energy related to the structural arrangement of atoms or molecules. This arrangement may be the result of chemical bonds within a molecule or otherwise. Chemical energy of a chemical substance can be transformed to other forms of energy by a chemical reaction. As an example, when a fuel is burned the chemical energy is converted to heat, same is the case with digestion of food metabolized in a biological organism. Green plants transform solar energy to chemical energy through the process known as photosynthesis, and electrical energy can be converted to chemical energy through electrochemical reactions.
The similar term chemical potential is used by chemists to indicate the potential of a substance to undergo a chemical reaction.
In the most basic layman terms possible when you discuss chemical potential, you are talking about the energy of the components that make up the system.
The chemical potential of a molecule depends on the bonds it forms, how easily these can be broken, what they react with and how much energy is released/absorbed in a reaction etc.
The chemical potential (energy) of the pure component therefore won't be the same as the chemical potential of the component when diluted by an impurity. The equations show how this works.
Have you done free energy calculations? This is essentially a chemical potential calculation.
and don't feel so bad about not getting it: The chemical potential
A vague discomfort at the thought of the chemical potential is still characteristic of a physics education. This intellectual gap is is due to the obscurity of the writings of J. Willard Gibbs who discovered and understood the matter 100 years ago.
Because physicists look down on chemistry, don't learn it well and teach it even less well. I found that chemists (at least physical chemists) have a much better intuitive and quantitative understanding of thermodynamics. Physicists rarely talk about the chemical potential as chemistry is too messy. In addition, Physicists tend to go straight to statistical mechanics thinking that the manipulation of thermodynamic potentials is a trivial matter once you have a partition function, which is not the case. En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma
Not really to nitpick since I am not sure I fully understand it myself, but it appears that chemical potential has to do with colligative properties which
depend on the number of molecules in a given volume of solvent and not on the properties (e.g. size or mass) of the molecules.
There are some articles I came across which made the distinction between chemical potential and the free energy (Gibbs energy) of the system which do get confused and I'm guilty of that.
It is why I asked if the Twank had done free energy calculations because the difference in energy (either absorbed or released) when a reaction takes place is a chemical potential calculation effectively.
In the case of salt in water, in a given volume, the addition of salt which splits into two ions, effectively dilutes the solvent and decreases the chemical potential - the values can be plugged into the right equations to show the effect that has in reducing freezing point etc.
Gibbs Free Energy and Pressure, Chemical Potential, Fugacity
Gibbs free energy per mole of substance ... This quantity is called the chemical potential and it is given the symbol, μ
Chemical potentials
In an aqueous solution of salt or of another solute, the chemical potential of water is lower than the chemical potential of pure water. The chemical potentials of pure ice and pure water vapor however, are independent of the composition of the solution from which it was formed. At equilibrium water will be in the state that has the lowest chemical potential. Therefore an aqueous solution has a lower freezing point and a higher boiling point (lower vapor pressure) than pure water.
But in terms of trying to find an explanation that can help to visualise how that happens I always look at how the molecules interact because it helps me to find some logic to help the concepts stick. Ad astra per aspera
The Gibbs Free Energy does not incorporate quantities of matter or chemical potential. Gibbs realised that when the quantity of matter can change, you need an additional energy term proportional to the quantity of matter and you define chemical potential as, (for instance) the Gibbs Free Energy per mole of substance at constant temperature and pressure. Of course, adding matter to a system at constant temperature and pressure requires increasing the volume of the system, but that's okay... En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma
Thank you for the help on the P. Chem.
Later! In the end, might makes right. Nothing has changed since the caveman.
