The liquid state is one of the primary states of matter characterized by having a definite volume with no fixed shape. In essence, liquids can be said to flow and acquire the shape of their container while maintaining a constant volume. Some examples of liquids encountered in everyday life include water, milk, and oil. The liquid state is of foremost importance in the sphere of human life for a number of biological and practical reasons. For instance, water is crucial for living organisms. Water plays an integral role in the digestion, circulation, and regulation of body temperature in the human body. Liquids in cooking and cleaning make daily routine tasks easier to manage. The liquid state gives substances the capability for easy mixing among themselves; this enables the formation of solutions that can range from beverages to medicines. Moreover, liquids play an important role in the industrial process—for example, as lubricants of machines. This function makes the running of the machine very smooth, with less friction and wear. This ability to flow and take up varied shapes of containers makes liquids very useful and irreplaceable in most applications, from household uses to complex industrial operations. Thus, the liquid state of matter
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Liquid State
Intermolecular forces are stronger in the liquid state than in the gaseous state. Molecules in liquids are so close that there is very little empty space between them and under normal conditions liquids are denser than gases. Molecules of liquids are held together by attractive intermolecular forces. Liquids have a definite volume because molecules do not separate from each other. However, molecules of liquids can move past one another freely, therefore, liquids can flow, can be poured, and can assume the shape of the container in which these are stored. In the following sections, we will look into some of the physical properties of liquids such as vapor pressure, surface tension, and viscosity.
Vapor Pressure
At a particular temperature, it is the pressure exerted by vapors over the liquid surface when vapors are in equilibrium with the liquid.
Surface Tension
It is the force at right angles to the surface of a liquid along one cm or one-meter length of the surface.
Viscosity
For a better understanding of the topic and to learn more about Liquid State with video lesson we provide the link to the
YouTube video:
Example 1: With the increase in temperature, how does the surface tension of a liquid change?
1)Increases
2) Decreases
3)Remain same
4)Nothing can be predicted
Solution
With the increase in temperature, the intermolecular forces of attraction decrease. Because of this temperature increase, the molecules' kinetic energy also increases, and thus, the surface tension decreases.
Hence, the answer is the option (2).
Example 2: An increase in kinetic energy can overcome intermolecular forces of attraction. How will the viscosity of liquid be affected by the increase in temperature?
1)No effect
2) Decrease
3)Increase
4)Nothing can be predicted
Solution
Effect of Temperature on Viscosity
With increasing temperature, viscosity decreases as the average thermal energy of molecules increases; hence, the effect of intermolecular attraction forces decreases.
It can be shown by the Arrhenius equation as follows:
$\eta=\mathrm{Ae}^{\mathrm{E}_{\mathrm{a}} / \mathrm{RT}}$
Here, T = Temperature, R = Universal gas constant, Ea = Activation energy.
With the increase in kinetic energy, intermolecular forces of attraction decrease. Thus, due to this decrease, the viscosity also decreases.
Hence, the answer is the option (2).
Example 3: Soap helps in cleaning clothes, because
1)Chemicals of soap change
2)It increases the surface tension of the solution
3)It absorbs the dirt
4) It lowers the surface tension of the solution
Solution
As we learned in Surface tension due to surface tension, liquids tend to minimize their surface area.
Thus, Soap helps to lower the surface tension of the solution, thus soap sticks to the dust particles and grease, and these are removed by action of water.
Hence, the answer is the option (4).
Example 4: On increasing temperature, the viscosity of liquid:
1)Increases
2) Decreases
3)Remain same
4)None of these
Solution
Viscosity
As we learned in Viscosity - The viscosity of liquids decreases as the temperature rises.
Viscosity of liquid $\alpha \frac{1}{\text { temperature }}$
Hence, the answer is the option (2).
Summary
The liquid state of matter has two features: it maintains a definite volume but takes a shape that will fit its container. Examples are water, milk, and oil—all products in use every day. For instance, one drinks, cooks, and cleans with these liquids. Water is, however, very important for life as it helps the body to hydrate, transport nutrients, and control the body temperature. In cooking, liquids are essential in the preparation and mixing of foodstuffs to come up with different foods that are rich in nutritional value. Liquids can be used in cleaning—dissolution of dirt, and hence clean or disinfecting. Some industrial applications include lubrication. The flowability and mixability of liquids permit the preparation of solutions, which form the backbone in many industries related to medicine or chemical fabrication. In general, life without the liquid state is unthinkable: a state that underpins biological functions eases household chores, and makes possible a large array of industrial processes—a real importance-loaded state in many spheres.
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