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

When you pour a glass of water, or to fill a vehicle with gasoline, you observe the water and also gasoline flow freely. Yet when you pour syrup ~ above pancakes or include oil to a auto engine, you note that syrup and motor oil do not flow as readily. The viscosity of a liquid 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, motor oil, and other liquids that carry out not flow freely, choose those displayed in (Figure), have higher viscosities. We deserve to measure viscosity by measuring the rate at which a metal ball drops through a fluid (the sphere falls more slowly with a more viscous liquid) or by measure up the rate at which a fluid flows through a narrow tube (more viscous liquids flow more slowly).

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(a) Honey and (b) motor oil are instances of liquids with high viscosities; they flow slowly. (credit a: alteration of occupational by Scott Bauer; credit transaction b: change of work-related by David Nagy)


Surface stress is defined as the energy required to boost the surface ar area that a liquid, or the force required to rise the size of a liquid surface by a given amount. This building results from the cohesive forces in between molecules in ~ the surface ar of a liquid, and also it reasons the surface ar of a fluid to behave choose a stretched rubber membrane. Surface ar tensions of numerous liquids room presented in (Figure). Among common liquids, water exhibits a patent high surface stress due to solid hydrogen bonding between its molecules. As a an outcome of this high surface ar tension, the surface of water represents a reasonably “tough skin” that have the right to withstand significant force there is no breaking. A stole needle closely placed ~ above water will certainly float. Some insects, choose the one presented in (Figure), also though they room denser than water, move on its surface because they space supported through the surface ar tension.

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


If you location one end of a file towel in spilled wine, as shown in (Figure), the fluid wicks increase the record towel. A similar procedure occurs in a fabric towel once you use it to dry turn off after a shower. This are instances of capillary action—when a fluid flows within a porous material due to the attraction that the fluid molecules to the surface ar of the material and also to various other liquid molecules. The adhesive forces in between the liquid and the porous material, an unified with the cohesive forces within the liquid, might be strong enough to relocate the liquid upward against gravity.

Wine wicks up a document towel (left) due to the fact that of the solid attractions that water (and ethanol) molecules to the −OH groups on the towel’s cellulose fibers and also the strong attractions that water molecule to various other water (and ethanol) molecule (right). (credit photo: alteration of work-related by mark Blaser)


The Newton is characterized as a kg m/s2, and so the provided surface stress is indistinguishable to 0.07199 kg/s2. The noted density have to be converted into units that will certainly cancel appropriately: ρ = 1000 kg/m3. The diameter that the tube in meters is 0.00025 m, so the radius is 0.000125 m. For a glass tube immersed in water, the call angle is θ = 0°, therefore cos θ = 1. Finally, acceleration because of gravity top top the planet is g = 9.8 m/s2. Substituting this values into the equation, and cancelling units, us have:

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


diameter = 0.36 mm

Biomedical Applications the Capillary Action

Many medical tests require drawing a little amount the blood, for example to determine the quantity of glucose in someone with diabetes or the hematocrit level in one athlete. This procedure deserve to be quickly done due to the fact that of capillary action, the capacity of a liquid to flow up a small tube versus gravity, as displayed in (Figure). When your finger is pricked, a drop of blood forms and also holds together as result of surface tension—the unbalanced intermolecular attractions at the surface ar of the drop. Then, once the open end of a narrow-diameter glass tube touches the drop of blood, the adhesive forces in between the molecules in the blood and also those in ~ the glass surface draw the blood up the tube. How much the blood goes up the tube relies on the diameter of the tube (and the form of fluid). A little tube has actually a relatively large surface area because that a given volume that blood, which outcomes in bigger (relative) attractive forces, permitting the blood to be attracted farther increase the tube. The liquid itself is organized together by its own cohesive forces. When the weight of the fluid in the pipe generates a downward force equal to the upward force associated with capillary action, the fluid stops rising.

Blood is built up for medical analysis by capillary action, i m sorry draws blood into a small 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 relying on their chemical identities and an outcome in matching variations in assorted physical properties. Cohesive forces between like molecules space responsible for a liquid’s viscosity (resistance to flow) and also surface anxiety (elasticity that a fluid surface). Adhesive forces in between the molecule of a liquid and also different molecules composing a surface in contact with the liquid room responsible for phenomena such as surface wetting and capillary rise.

The test tubes presented here save equal amounts of the mentioned motor oils. Identical metal spheres to be dropped in ~ the very same time into each that the tubes, and also a brief moment later, the spheres had actually fallen come the heights suggested in the illustration.

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


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

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

You may have heard someone use the figure of decided “slower 보다 molasses in winter” to explain a procedure that occurs slowly. Define why this is an apt idiom, using concepts of molecular size and also shape, molecule interactions, and also the effect of an altering temperature.

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

It is often recommended the you permit your car engine operation idle to warmth up prior to driving, particularly on cold winter days. While the benefit of an extensive idling is dubious, that is definitely true the a warmth engine is more fuel effective than a cold one. Define the reason for this.

The surface ar tension and also viscosity of water at several different temperatures are given in this table.

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

(a) as temperature increases, what happens to the surface tension of water? define why this occurs, in regards to molecular interactions and the effect of transforming temperature.

(b) as temperature increases, what wake up to the viscosity that water? define why this occurs, in regards to molecular interactions and also the result of changing temperature.

(a) as the water reaches greater temperatures, the increased kinetic energies of its molecule are much more effective in overcoming hydrogen bonding, and also so the surface tension decreases. Surface ar tension and intermolecular pressures are straight related. (b) The very same trend in viscosity is viewed as in surface tension, and also for the very same reason.

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At 25 °C, just how high will certainly water climb in a glass capillary tube through an inside diameter the 0.63 mm? describe (Figure) because that the compelled information.

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


adhesive forceforce that attraction in between molecules of various chemical identitiescapillary actionflow of fluid within a porous material due to the attraction the the liquid molecules to the surface ar of the material and to other liquid moleculescohesive forceforce the attraction in between identical moleculessurface tensionenergy forced to rise the area, or length, of a liquid surface ar by a provided amountviscositymeasure of a liquid’s resistance to flow