Distinguish in between adhesive and cohesive forcesDefine viscosity, surchallenge anxiety, and also capillary riseDescribe the duties of intermolecular attractive pressures in each of these properties/phenomena

When you pour a glass of water, or fill a car via gasoline, you observe that water and gasoline flow freely. But when you pour syrup on pancakes or add oil to a car engine, you note that syrup and motor oil execute not circulation as conveniently. The viscosity of a liquid is a measure of its resistance to flow. Water, gasoline, and also other liquids that circulation freely have actually a low viscosity. Honey, syrup, motor oil, and other liquids that do not circulation openly, like those presented in (Figure), have higher viscosities. We deserve to measure viscosity by measuring the rate at which a steel ball falls with a liquid (the sphere falls even more gradually with a more viscous liquid) or by measuring the price at which a liquid flows via a narrow tube (even more viscous liquids circulation even more slowly).

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


Surchallenge anxiety is defined as the energy required to boost the surchallenge area of a liquid, or the force required to rise the size of a liquid surchallenge by a provided amount. This home results from the cohesive forces in between molecules at the surconfront of a liquid, and also it causes the surconfront of a liquid to behave actually favor a extended rubber membrane. Surconfront tensions of numerous liquids are presented in (Figure). Amongst prevalent liquids, water exhibits a distinctly high surconfront tension due to strong hydrogen bonding between its molecules. As a result of this high surface stress, the surchallenge of water represents a relatively “challenging skin” that have the right to withstand also substantial force without breaking. A steel needle carefully placed on water will float. Some insects, favor the one shown in (Figure), even though they are denser than water, relocate on its surface because they are supported by the surface stress.

Surchallenge Tensions of Usual Substances at 25 °CSubstanceFormulaSurface Tension (mN/m)
ethylene glycolCH2(OH)CH2(OH)47.99


If you area one finish of a document towel in spilled wine, as displayed in (Figure), the liquid wicks up the paper towel. A similar procedure occurs in a cloth towel as soon as you use it to dry off after a shower. These are examples of capillary action—once a liquid flows within a porous material because of the attractivity of the liquid molecules to the surconfront of the product and also to various other liquid molecules. The adhesive forces between the liquid and also the porous product, unified with the cohesive forces within the liquid, might be solid sufficient to move the liquid upward against gravity.

Wine wicks up a document towel (left) bereason of the strong attractions of water (and also ethanol) molecules to the −OH teams on the towel’s cellulose fibers and also the solid attractions of water molecules to various other water (and also ethanol) molecules (right). (credit photo: modification of occupational by Mark Blaser)


The Newton is identified as a kg m/s2, and also so the offered surconfront stress and anxiety is identical to 0.07199 kg/s2. The provided thickness need to be converted into systems that will certainly cancel appropriately: ρ = 1000 kg/m3. The diameter of the tube 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°, so cos θ = 1. Finally, acceleration due to gravity on the earth is g = 9.8 m/s2. Substituting these values into the equation, and also cancelling systems, we have:

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


diameter = 0.36 mm

Bioclinical Applications of Capillary Action

Many kind of clinical tests need drawing a tiny amount of blood, for instance to recognize the amount of glucose in someone with diabetes or the hematocrit level in an athlete. This procedure can be quickly done bereason of capillary action, the ability of a liquid to flow up a little tube versus gravity, as shown in (Figure). When your finger is pricked, a drop of blood forms and also holds together because of surface tension—the unbalanced intermolecular attractions at the surconfront of the drop. Then, when the open finish of a narrow-diameter glass tube touches the drop of blood, the adhesive pressures between the molecules in the blood and also those at the glass surchallenge draw the blood up the tube. How far the blood goes up the tube relies on the diameter of the tube (and also the kind of fluid). A little tube has actually a fairly large surchallenge area for a provided volume of blood, which outcomes in larger (relative) attrenergetic pressures, allowing the blood to be drawn farther up the tube. The liquid itself is hosted together by its own cohesive pressures. When the weight of the liquid in the tube generates a downward pressure equal to the upward force linked via capillary action, the liquid stops rising.

Blood is collected for clinical analysis by capillary activity, which draws blood into a little diameter glass tube. (credit: modification of work by Centers for Disease Control and also Prevention)

Key Concepts and Summary

The intermolecular forces between molecules in the liquid state vary depending upon their chemical identities and also cause corresponding variations in various physical properties. Cohesive forces in between like molecules are responsible for a liquid’s viscosity (resistance to flow) and also surconfront anxiety (elasticity of a liquid surface). Adhesive pressures in between the molecules of a liquid and various molecules composing a surface in contact through the liquid are responsible for sensations such as surface wetting and also capillary rise.

The test tubes presented below contain equal amounts of the mentioned motor oils. Identical steel spheres were dropped at the exact same time right into each of the tubes, and a brief moment later, the spheres had fallen to the heights shown in the illustration.

Rank the motor oils in order of raising viscosity, and also describe your reasoning:


(a) Exsimple their distinctions in viscosity in terms of the size and form of their molecules and also their IMFs.

(b) Explain their differences in surchallenge tension in regards to the dimension and also shape of their molecules and also their IMFs:

You may have actually heard someone use the number of speech “sreduced than molasses in winter” to define a procedure that occurs progressively. Exsimple why this is an apt idiom, making use of principles of molecular dimension and form, molecular interactions, and also the impact of transforming temperature.

Temperature has an impact on intermolecular forces: The greater the temperature, the greater the kinetic energies of the molecules and also the better the degree to which their intermolecular pressures are get over, and so the even more fluid (less viscous) the liquid. The lower the temperature, the much less the intermolecular forces are get rid of, and so the less viscous the liquid.

It is frequently recommended that you let your car engine run idle to heat up prior to driving, particularly on cold winter days. While the advantage of expanded idling is dubious, it is definitely true that a warmth engine is more fuel effective than a cold one. Exordinary the reason for this.

The surchallenge anxiety and viscosity of water at numerous different temperatures are offered in this table.

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

(a) As temperature boosts, what happens to the surconfront stress and anxiety of water? Exsimple why this occurs, in terms of molecular interactions and also the effect of transforming temperature.

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

(a) As the water reaches better temperatures, the increased kinetic energies of its molecules are more efficient in overcoming hydrogen bonding, and also so its surconfront anxiety decreases. Surconfront stress and also intermolecular pressures are directly associated. (b) The very same trend in viscosity is seen as in surchallenge tension, and for the very same reason.

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At 25 °C, how high will certainly water rise in a glass capillary tube through an inner diameter of 0.63 mm? Refer to (Figure) for the required indevelopment.

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


adhesive forcepressure of attractivity between molecules of various chemical identitiescapillary actionflow of liquid within a porous material because of the attractivity of the liquid molecules to the surconfront of the material and also to other liquid moleculescohesive forceforce of attractivity between similar moleculessurface tensionenergy forced to increase the location, or size, of a liquid surconfront by a offered amountviscositymeasure of a liquid’s resistance to flow