Distinguish in between adhesive and also cohesive forcesDefine viscosity, surface ar tension, and capillary riseDescribe the functions of intermolecular attractive forces in every of these properties/phenomena

When you pour a glass of water, or fill a auto with gasoline, friend observe the water and gasoline circulation freely. But when you pour syrup ~ above pancakes or add oil to a auto engine, you note that syrup and also motor oil execute not flow as readily. The viscosity that a fluid is a measure up of that is resistance to flow. Water, gasoline, and also other liquids that flow freely have actually a low viscosity. Honey, syrup, engine oil, and other liquids that do not flow freely, prefer those shown in (Figure), have higher viscosities. We deserve to measure viscosity by measure up the rate at i m sorry a steel ball falls through a liquid (the sphere falls an ext slowly v a an ext viscous liquid) or by measuring the rate at which a liquid flows v a narrow tube (more viscous liquids flow an ext slowly).

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(a) Honey and (b) engine oil are instances of liquids through high viscosities; they circulation slowly. (credit a: change of work-related by Scott Bauer; credit transaction b: modification of job-related by David Nagy)


Surface stress and anxiety is defined as the power required to boost the surface area that a liquid, or the force required to increase the size of a liquid surface ar by a provided amount. This property results from the cohesive forces between molecules at the surface of a liquid, and also it causes the surface of a fluid to behave like a stretched rubber membrane. Surface tensions of numerous liquids space presented in (Figure). Amongst common liquids, water exhibits a patent high surface anxiety due to strong hydrogen bonding in between its molecules. As a an outcome of this high surface ar tension, the surface of water represents a reasonably “tough skin” that deserve to withstand considerable force there is no breaking. A steel needle carefully placed on water will float. Part insects, choose the one presented in (Figure), even though they room denser 보다 water, move on that is surface because they are supported through the surface ar tension.

Surface stress of usual Substances in ~ 25 °CSubstanceFormulaSurface tension (mN/m)
ethylene glycolCH2(OH)CH2(OH)47.99


If you place one end of a file towel in spilled wine, as displayed in (Figure), the fluid wicks increase the document towel. A similar procedure occurs in a towel towel once you use it to dry off after a shower. These are examples of capillary action—when a liquid flows in ~ a porous material due to the attraction of the fluid molecules to the surface ar of the material and also to other liquid molecules. The adhesive forces in between the liquid and the porous material, merged with the cohesive forces within the liquid, might be solid enough to move the liquid upward versus gravity.

Wine wicks up a record towel (left) due to the fact that of the strong attractions of water (and ethanol) molecules to the −OH teams on the towel’s cellulose fibers and also the solid attractions that water molecules to various other water (and ethanol) molecules (right). (credit photo: change of occupational by mark Blaser)


The Newton is characterized as a kg m/s2, and also so the detailed surface stress and anxiety is tantamount to 0.07199 kg/s2. The detailed density need to be converted right into units that will cancel appropriately: ρ = 1000 kg/m3. The diameter of the pipe in meters is 0.00025 m, so the radius is 0.000125 m. For a glass tube immersed in water, the contact angle is θ = 0°, therefore cos θ = 1. Finally, acceleration as result of gravity top top the earth is g = 9.8 m/s2. Substituting this values right into the equation, and also cancelling units, we have:

Check Your finding out Water rises in a glass capillary pipe to a elevation of 8.4 cm. What is the diameter the the capillary tube?


diameter = 0.36 mm

Biomedical Applications that Capillary Action

Many medical tests require illustration a tiny amount of blood, for instance to identify the lot of glucose in someone through diabetes or the hematocrit level in one athlete. This procedure have the right to be conveniently done because of capillary action, the ability of a liquid to flow up a small tube against gravity, as shown in (Figure). Once your finger is pricked, a fall of blood forms and holds together because of surface tension—the unbalanced intermolecular attractions in ~ the surface of the drop. Then, as soon as the open end of a narrow-diameter glass tube touches the autumn of blood, the adhesive forces in between the molecule in the blood and also those in ~ the glass surface attract the blood increase the tube. How much the blood goes up the tube counts on the diameter that the tube (and the form of fluid). A little tube has actually a relatively big surface area for a given volume of blood, which outcomes in larger (relative) attractive forces, allowing the blood come be attracted farther increase the tube. The fluid itself is hosted together through its very own cohesive forces. As soon as the load of the fluid in the tube generates a downward force equal to the increase force linked with capillary action, the fluid stops rising.

Blood is accumulated for medical analysis by capillary action, i m sorry draws blood right into a little diameter glass tube. (credit: change of work by Centers for condition Control and also Prevention)

Key Concepts and Summary

The intermolecular forces in between molecules in the fluid state vary depending upon their chemical identities and an outcome in matching variations in miscellaneous physical properties. Cohesive forces between like molecules room responsible because that a liquid’s viscosity (resistance come flow) and also surface anxiety (elasticity the a fluid surface). Adhesive forces in between the molecule of a liquid and also different molecules writing a surface in contact with the liquid are responsible because that phenomena together as surface wetting and also capillary rise.

The check tubes shown here contain equal amounts of the stated motor oils. The same metal spheres were dropped at the same time right into each the the tubes, and also a short moment later, the spheres had actually fallen to the heights indicated in the illustration.

Rank the motor oil in bespeak of increasing viscosity, and also explain her reasoning:


(a) define their differences in viscosity in terms of the size and shape of their molecules and their IMFs.

(b) define their distinctions in surface tension in regards to the size and also shape of their molecules and their IMFs:

You may have actually heard someone usage the number of speech “slower than molasses in winter” to explain a procedure that wake up slowly. Explain why this is one apt idiom, using concepts of molecular size and also shape, molecular interactions, and also the impact of changing temperature.

Temperature has actually an impact on intermolecular forces: The higher the temperature, the higher the kinetic energies of the molecules and also the better the degree to which your intermolecular pressures are overcome, and also so the more fluid (less viscous) the liquid. The lower the temperature, the less the intermolecular forces are overcome, and also so the much less viscous the liquid.

It is often recommended the you allow your car engine run idle to heat up prior to driving, particularly on cold winter days. When the benefit of prolonged idling is dubious, it is certainly true that a heat engine is much more fuel reliable than a cold one. Define the reason for this.

The surface tension and viscosity that water in ~ several various temperatures are provided in this table.

WaterSurface stress (mN/m)Viscosity (mPa s)
0 °C75.61.79
20 °C72.81.00
60 °C66.20.47
100 °C58.90.28

(a) together temperature increases, what wake up to the surface stress of water? describe why this occurs, in terms of molecular interactions and the result of changing temperature.

(b) as temperature increases, what happens to the viscosity the water? explain why this occurs, in terms of molecular interactions and the effect of transforming temperature.

(a) together the water reaches higher temperatures, the raised kinetic energies of its molecule are an ext effective in overcoming hydrogen bonding, and also so the surface tension decreases. Surface ar tension and also intermolecular pressures are directly related. (b) The same trend in viscosity is seen as in surface ar tension, and for the same reason.

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At 25 °C, exactly how high will water climb in a glass capillary tube v an inner diameter of 0.63 mm? refer to (Figure) for the forced information.

Water rises in a glass capillary pipe to a height of 17 cm. What is the diameter of the capillary tube?


adhesive forceforce the attraction in between molecules of various chemical identitiescapillary actionflow of liquid within a porous material as result of the attraction the the liquid molecules come the surface ar of the material and also to other liquid moleculescohesive forceforce of attraction between identical moleculessurface tensionenergy forced to increase the area, or length, the a liquid surface by a offered amountviscositymeasure that a liquid’s resistance come flow