Monthly Archives: December 2016

[Explanation] What is Viscosity? 

Viscosity of a liquid implies the viscous force that tends to prevent the relative motion of a liquid layer compared to another layer in its contact.

The coefficient of viscosity ‘n’ is the numerical measure of viscosity, and it is defined as the frictional force, F per unit area per unit velocity gradient i.e., 

n= F/{A(dv/dx)}

Where, 

A is the surface area and

dv/dx is the velocity gradient.
On addition of a solute having larger molecular size and increased intermolecular forces, the coefficient of viscosity of water increases. Thus, addition of a solute increases the viscosity of water. With increase in its concentration, the viscosity of the solution is increased further.


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​যাহার শক্তি শুশিয়া জয়িলা ভুবন,

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সময় থাকিতে করিলা যারে হেলা;

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[Explanation] Boiling Point Elevation: Cause & Effect

Introduction:

Boiling point elevation describes the phenomenon that the boiling point of liquid (a solvent) will be higher when a non volatile solute is dissolved in it than when it is pure.

Cause and Effect :

Boiling point elevation is the reduction of chemical potential of the liquid solvent as a result of the presence of a non-volatile solute. The physical basis of lowering of chemical potential is entropic.
In the absence of solute, the pure liquid solvent has an entropy that reflects its disorder. Its vapour pressure reflects the tendency of the liquid to change towards greater entropy, which can be achieved if the liquid is vaporized to form a more chaotic gas. When a solute is present, there is an additional contributions to the entropy of the liquid. Since there is already an additional randomness in the liquid, the system reaches its maximum entropy. When less liquid evaporates then the solute, and the randomness it causes is absent. The effect of the solute is a lower vapour pressure and hence a higher boiling point.
Thanks for reading 🙂