La particolare struttura dell’acqua 
L’acqua una molecola essenziale per la vita di ogni essere umano è formata da due atomi di idrogeno e uno di ossigeno inoltre presenta una forte elettronegatività dell'atomo di ossigeno che attrae verso di sé gli elettroni impegnati nei legami covalenti, producendo uno sbilanciamento di cariche tra le parti della molecola che risulta quindi un dipolo: un'estremità ha carica negativa, l'altra positiva.
Questo semplice fatto produce interazioni between the same water molecules, between water and ions between water and macromolecules, such as to trigger chains of consequences that occur in the most diverse and important phenomena, to what happens in the macroscopic world in which we live.
The surface tension
actions attractions between molecules of a liquid (the forces of cohesion ) mean that the 
molecules of the surface layer are not subjected to the force resulting
nothing that tends to move them inwards, therefore, they tend to escape from
limit surface of the liquid and therefore, this tends to have the extension
minimum possible.
molecules on the surface have a potential energy
higher than that of molecules in the liquid, so if you want to increase the extent of
free surface of a liquid should be proportional to the increase
spend energy surface.
molecules of the surface layer are not subjected to the force resulting
nothing that tends to move them inwards, therefore, they tend to escape from
limit surface of the liquid and therefore, this tends to have the extension
minimum possible.
molecules on the surface have a potential energy
higher than that of molecules in the liquid, so if you want to increase the extent of
free surface of a liquid should be proportional to the increase
spend energy surface.
If the liquid undergoes a transformation that alters only its
surface S, there is a variation of internal energy, ΔU, which is practically equal
the variation of potential energy of the surface layer, and therefore proportional to the increase ΔS
surface. This change in internal energy is in part (Q) provided by
' kinetic energy of the molecules of the environment and in part (L) corresponding to a
mechanical work that must be supplied from outside.
is defined as surface tension (or surface free energy) of a liquid
amount of work required to increase the extent of its surface of a
units maintaining a constant temperature of system, ie the increase in energy
freedom (Df = ΔU-Q) per unit area. The widespread
surface S, there is a variation of internal energy, ΔU, which is practically equal
the variation of potential energy of the surface layer, and therefore proportional to the increase ΔS
surface. This change in internal energy is in part (Q) provided by
' kinetic energy of the molecules of the environment and in part (L) corresponding to a
mechanical work that must be supplied from outside.
is defined as surface tension (or surface free energy) of a liquid
amount of work required to increase the extent of its surface of a
units maintaining a constant temperature of system, ie the increase in energy
freedom (Df = ΔU-Q) per unit area. The widespread
The capillary is the set of phenomena due to interactions between molecules a liquid and a solid on their surface of separation.
It occurs on the surface of the liquid in contact with solid raised
that can occur (in the case of 'water ), since the adhesion forces between the water and the container that contains
are greater than the cohesive forces between the water molecules, or
depressed (eg mercury ) than the rest of the surface, because in this case are the
cohesive forces prevail over the forces of adhesion. The forces that occur are
cohesion, the ' adesione e la tensione superficiale .
Calore specifico
Il calore specifico di una sostanza è la quantità di calore che permette di far variare
la sua temperatura di 1°C. Nel caso dell'acqua il calore specifico è molto elevato 4,19
KJ/Kg. Occorre quindi molta energia per far variare di un grado centigrado la
temperatura dell'acqua e questo rallenta le variazioni di temperatura. Le correnti
oceaniche trasportano grandi quantità di calore.
Il calore specifico di una sostanza è la quantità di calore che permette di far variare
la sua temperatura di 1°C. Nel caso dell'acqua il calore specifico è molto elevato 4,19
KJ/Kg. Occorre quindi molta energia per far variare di un grado centigrado la
temperatura dell'acqua e questo rallenta le variazioni di temperatura. Le correnti
oceaniche trasportano grandi quantità di calore.
L’acqua come solvente
Quando un composto ionico o polare viene messo
in acqua, viene circondato dalle molecole
of water which, because of their small size,
fit between an ion and another or between one molecule and the other
solute
targeted especially to be presented to each ion (or polar end) of
solute the part of himself bearing the opposite charge, and this weakens the attraction between the ions
(or between the polar molecules) and breaks the crystal structure. Each ion (or any
polar molecule) is found then solvated,
that is completely surrounded by water molecules. An example of a solute ion is the common salt (sodium chloride
), an example of molecular polar solute is sugar. In general, polar substances
ion, such as acids, alcohols and salts are quite soluble in water, while not
are non-polar substances such as fats and oils. The non-polar molecules do not mix
water because it is energetically favored the formation of hydrogen bonds
inside, rather than forming ties with Van der Waals
nonpolar molecules.
Quando un composto ionico o polare viene messo
in acqua, viene circondato dalle molecole
of water which, because of their small size,
fit between an ion and another or between one molecule and the other
solute
targeted especially to be presented to each ion (or polar end) of
solute the part of himself bearing the opposite charge, and this weakens the attraction between the ions
(or between the polar molecules) and breaks the crystal structure. Each ion (or any
polar molecule) is found then solvated,
that is completely surrounded by water molecules. An example of a solute ion is the common salt (sodium chloride
), an example of molecular polar solute is sugar. In general, polar substances
ion, such as acids, alcohols and salts are quite soluble in water, while not
are non-polar substances such as fats and oils. The non-polar molecules do not mix
water because it is energetically favored the formation of hydrogen bonds
inside, rather than forming ties with Van der Waals
nonpolar molecules.
No comments:
Post a Comment