Nature Of Liquids

Let Us learn and understand properties of liquids

a) Liquid particles are always in motion, Liquid particles are free to slide past one another.
b) liquids can both FLOW
c) However, liquid particles are attracted to each other, whereas gases are not
d) Particles of a liquid spin and vibrate while they move, thus contributing to their average kinetic energy
e) But, most of the particles do not have enough energy to escape into the gaseous state; they would have to overcome their intermolecular attractions with other particles
f) The intermolecular attractions also reduce the amount of space between particles of a liquid Thus, liquids are more dense than gases
g) Increasing pressure on liquid has hardly an effect on it’s volume
h) Water in an open vessel or puddle eventually goes into the air
i) Increasing the pressure also has little effect on the volume of a solid For that reason, liquids and solids are known as the condensed states of matter
j) The conversion of a liquid to a gas or vapor is called vaporization.When this occurs at the surface of a liquid that is not boiling, the process is called evaporation
k) Some of the particles break away and enter the gas or vapor state; but only those with the
minimum kinetic energy
l) A liquid will also evaporate faster when heated Because the added heat increases the average
kinetic energy needed to overcome the attractive forces
m) Cooling occurs because those with the highest energy escape first
n) The vapor pressure of a liquid can be determined by a device called a manometer
o) The boiling point (bp) is the temperature at which the vapor pressure of the liquid is just equal to the external pressure.

We can investigate pressure in a liquid by using the apparatus shown in figure below

It is a simple pressure gauge and it measures differences in pressure exerted at the two ends of the apparatus. It is called manometer. The mouth of a thistle funnel is tightly covered with a thin plastic sheet. The thistle funnel is connected to a U-tube manometer containing water, by a rubber tubing. If you press the plastic sheet lightly with a finger, the air inside the manometer gets compressed and it exerts greater pressure at that end than the atmospheric pressure exerted at the open end of the U-tube. As a result, the liquid level alters and goes up in the other open arm of the U-tube. When the pressure exerted on the plastic sheet is greater, the difference in the levels (h) is also greater. This difference is the measure of the difference in the pressures at the two ends of the manometer.

Now, lower the mouth of the funnel into a glass vessel containing water. You will notice that the deeper it goes, greater is the difference in the levels of the water in the manometer. This indicates that the pressure in a liquid increases with depth.

Repeat the experiment by turning the thistle funnel in different directions keeping the depth constant. You will observe that as long as the depth remains the same there is no change in the level of the water in the manometer. Thus, the pressure exerted by a liquid at a given depth is the same in all directions

Now, lower the thistle funnel to the same depth in a number of liquids having different densities. You will notice that in liquids having greater density the pressure at the same depth is greater. This indicates that greater the density of the liquid, greater is the pressure at the same depth.