Case Study Questions Class 11 Chemistry Chapter 5 States of Matter
CBSE Class 11 Case Study Questions Chemistry States of Matter. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions States of Matter.
At Case Study Questions there will given a Paragraph. In where some Important Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks, 4 marks.
CBSE Case Study Questions Class 11 Chemistry States of Matter
Case –I
Chemical properties of a substance do not change withthe change of its physical state; but rate of chemicalreactions do depend upon the physical state. Many timesin calculations while dealing with data of experiments werequire knowledge of the state of matter. Therefore, itbecomes necessary for a chemist to know the physical laws which govern the behaviour of matter indifferent states. Intermolecular forces are the forces ofattraction and repulsion between interactingparticles (atoms and molecules). This termdoes not include the electrostatic forces thatexist between the two oppositely charged ionsand the forces that hold atoms of a moleculetogether i.e., covalent bonds.Attractive intermolecular forces are knownas van der Waals forces, in honour of Dutchscientist Johannes van der Waals (1837-1923) . van der Waals forces vary considerablyin magnitude and include dispersion forcesor London forces, dipole-dipole forces, anddipole-induced dipole forces. A particularlystrong type of dipole-dipole interaction ishydrogen bonding. Only a few elements canparticipate in hydrogen bond formation,therefore it is treated as a separatecategory.
Atoms and nonpolar molecules are electricallysymmetrical and have no dipole momentbecause their electronic charge cloud issymmetrically distributed. But a dipole maydevelop momentarily even in such atoms andmolecules. The temporary dipoles of two different atomattract each other. Similarly temporary dipolesare induced in molecules also. This force ofattraction was first proposed by the Germanphysicist Fritz London, and for this reasonforce of attraction between two temporary dipoles is known as London force. dispersion force forces are always attractive and interactionenergy is inversely proportional to the sixthpower of the distance between two interactingparticles (i.e.,1/r 6 where r is the distancebetween two particles). These forces areimportant only at short distances (~500 pm)and their magnitude depends on thepolarisability of the particle.
Dipole-dipole forces act between the moleculespossessing permanent dipole. Ends of thedipoles possess “partial charges” and thesecharges are shown by Greek letter delta (δ).Partial charges are always less than the unitelectronic charge (1.6×10–19 C). The polarmolecules interact with neighbouringmolecules. This interactionis stronger than the London forces but isweaker than ion-ion interaction because onlypartial charges are involved. The attractiveforce decreases with the increase of distancebetween the dipoles. As in the above case herealso, the interaction energy is inverselyproportional to distance between polarmolecules. Dipole-dipole interaction energybetween stationary polar molecules is proportional to 1/r3 and thatbetween rotating polar molecules is proportional to 1/r 6, where r is the distancebetween polar molecules.
Dipole–Induced Dipole Forcesare type of attractive forces operate betweenthe polar molecules having permanent dipoleand the molecules lacking permanent dipole.Permanent dipole of the polar moleculeinduces dipole on the electrically neutralmolecule by deforming its electronic cloud. Thus an induced dipole is developedin the other molecule. In this case alsointeraction energy is proportional to 1/r6where r is the distance between twomolecules. Induced dipole moment dependsupon the dipole moment present in thepermanent dipole and the polarisability of theelectrically neutral molecule.
[A] MCQ
1) Partial charges are always less than the unit electronic charge …
(a) (1.6×10–19 C)
(b) (1.6×10–18 C)
(c) (1.6×10–17 C)
(d) (1.6×10–16 C)
Ans- a) (1.6×10–19 C)
2) Temporary dipoles are induced in molecules also. ,this force of attraction was first proposed by ..
(a) Johannes van der Waals
(b) Fritz London
(c) Robert Boyle
(d) Joseph Lewis Gay Lussac
Ans-b) Fritz London
3) Atoms and nonpolar molecules are electrically ….
(a) Compositional
(b) Unsymmetrical
(c) Symmetrical
(d) All the above
Ans- c) Symmetrical
4) Partial Charges denoted by greek letter ….
(a) ε
(b) ζ
(c) δ
(d) η
Ans- c) δ
5) The attractive force … with the … of distance between the dipoles.
(a) increase , increase
(b) decrease , decrease
(c) increase , decrease
(d) decreases , increase
Ans- d) decreases , increase
[B] Short Answers
1) What are london forces ?
Ans- This force of attraction was first proposed by the German physicist Fritz London, and for this reason force of attraction between two temporary dipoles is known as London force. dispersion force forces are always attractive and interaction energy is inversely proportional to the sixth power of the distance between two interacting particles (i.e., 1/r 6 where r is the distance between two particles).
2) What are Dipole–Induced Dipole Forces ?
Ans-Induced Dipole Forces are type of attractive forces operate between the polar molecules having permanent dipole and the molecules lacking permanent dipole. Permanent dipole of the polar molecule induces dipole on the electrically neutral molecule by deforming its electronic cloud . Thus an induced dipole is developed in the other molecule.
3) Why it is necessary for a chemist to know the physical laws which govern the behaviour of matter indifferent states ?
Ans- Chemical properties of a substance do not change with the change of its physical state; but rate of chemical reactions do depend upon the physical state. Many times in calculations while dealing with data of experiments we require knowledge of the state of matter. Therefore, it becomes necessary for a chemist to know the physical laws which govern the behaviour of matter in different states.
[C] Long Answers
1) Explain Intermolecular Forces .
Ans- Intermolecular forces are the forces of attraction and repulsion between interacting particles (atoms and molecules). This term does not include the electrostatic forces that exist between the two oppositely charged ions and the forces that hold atoms of a molecule together i.e., covalent bonds. Attractive intermolecular forces are known as van der Waals forces, in honour of Dutch scientist Johannes van der Waals (1837- 1923) . van der Waals forces vary considerably in magnitude and include dispersion forces or London forces, dipole-dipole forces, and dipole-induced dipole forces. A particularly strong type of dipole-dipole interaction is hydrogen bonding. Only a few elements can participate in hydrogen bond formation, therefore it is treated as a separate category.
2) Explain Dipole Dipole forces .
Ans-Dipole-dipole forces act between the molecules possessing permanent dipole. Ends of the dipoles possess “partial charges” and these charges are shown by Greek letter delta (δ). Partial charges are always less than the unit electronic charge (1.6×10–19 C). The polar molecules interact with neighbouring molecules. This interaction is stronger than the London forces but is weaker than ion-ion interaction because only partial charges are involved. The attractive force decreases with the increase of distance between the dipoles. As in the above case here also, the interaction energy is inversely proportional to distance between polar molecules. Dipole-dipole interaction energy between stationary polar molecules is proportional to 1/r 3 and that between rotating polar molecules is proportional to 1/r 6 , where r is the distance between polar molecules.
Case –II
Hydrogen bond is found in the molecules in which highly polarN–H, O–H or H–F bonds are present. AlthoughHydrogen bonding is regarded as being limitedTo N, O and F; but species such as Cl mayAlso participate in hydrogen bonding. EnergyOf hydrogen bond varies between 10 to 100kJ mol–1. This is quite a significant amount ofenergy; therefore, hydrogen bonds arepowerful force in determining the structure andproperties of many compounds, for exampleproteins and nucleic acids. Strength of thehydrogen bond is determined by the coulombicinteraction between the lone-pair electrons ofthe electronegative atom of one molecule andthe hydrogen atom of other molecule. Thermal energy is the energy of a body arisingfrom motion of its atoms or molecules. It isdirectly proportional to the temperature of thesubstance. It is the measure of averagekinetic energy of the particles of the matterand is thus responsible for movement ofparticles. This movement of particles is calledthermal motion. When molecular interactions are veryWeak, molecules do not cling together to makeLiquid or solid unless thermal energy isReduced by lowering the temperature. GasesDo not liquify on compression only, althoughMolecules come very close to each other andIntermolecular forces operate to the maximum.However, when thermal energy of moleculesIs reduced by lowering the temperature; theGases can be very easily liquified. The gaseous state is the simplest state of matter.Throughout our life we remain immersed inThe ocean of air which is a mixture of gases.We spend our life in the lowermost layer ofThe atmosphere called troposphere, which isHeld to the surface of the earth by gravitationalForce. The thin layer of atmosphere is vital toOur life. It shields us from harmful radiationsAnd contains substances like dioxygen,Dinitrogen, carbon dioxide, water vapour, etc. The gaseous state is characterized by theFollowing physical properties.
- Gases are highly compressible.
- Gases exert pressure equally in allDirections.
- Gases have much lower density than theSolids and liquids.
- The volume and the shape of gases areNot fixed. These assume volume and shape of the container.
- Gases mix evenly and completely in allProportions without any mechanical aid.
Simplicity of gases is due to the fact thatThe forces of interaction between theirMolecules are negligible. Their behaviour isGoverned by same general laws, which wereDiscovered as a result of their experimentalStudies. These laws are relationships betweenMeasurable properties of gases. Some of theseProperties like pressure, volume, temperatureAnd mass are very important becauseRelationships between these variables describeState of the gas.
On the basis of his experiments, Robert BoyleReached to the conclusion that at constantTemperature, the pressure of a fixedAmount (i.e., number of moles n) of gasVaries inversely with its volume. This isKnown as Boyle’s law. Mathematically, it canBe written asp ∝1⇒p =k11
VV
Where k1 Is the proportionality constant. TheValue of constant k1 Depends upon theAmount of the gas, temperature of the gasAnd the units in which p and V are expressed. On rearranging equation we obtainpV = k1 .It means that at constant temperature,product of pressure and volume of a fixedamount of gas is constant.If a fixed amount of gas at constanttemperature T occupying volume V1 atpressure p1 undergoes expansion, so thatvolume becomes V2 and pressure becomes p2,Then according to Boyle’s law : P1V1 = P2V2= constant ⇒ P1=V2
P2.V1.
Charles’ law, which states thatPressure remaining constant, the volume of a fixed mass of a gas is directlyProportional to its absolute temperature. The lowest hypothetical or imaginaryTemperature at which gases are supposed toOccupy zero volume is called Absolute zero. AnotherThe mathematicalRelationship between pressure andTemperature was given by Joseph Gay LussacAnd is known as Gay Lussac’s law. It statesThat at constant volume, pressure of a fixedAmount of a gas varies directly with theTemperature. Mathematically,
P ∝T⇒ P= constant = k3
T
[A] MCQ
1) Which of the following element is not participates in hydrogen bonding ?
(a) C
(b) N
(c) O
(d) F
Ans- a) C
2) According to Boyle’s law
(a) p∝ V
(b) p∝1
V
(c) p= V
(d) p~ 1
V
Ans- b) p ∝1
V
3) Energy Of hydrogen bond varies between …
(1) 1 to 10 kJ mol–1.
(b) 1 to 100 kJ mol–1.
(c) 10 to 100 kJ mol–1.
(d) 10 to 20 kJ mol–1.
Ans- c) 10 to 100 kJ mol–1.
4) According to Gay Lussac’s law…
(a) p ∝ V
(b) p ∝1
V
(c) p ∝ 1
T
(d) p∝ T
Ans- d) p ∝ T
5) Gaseous can liquefy when intermolecular forces are …
(a) Maximum
(b) Minimum
(c) Constant
(d) None Of Above
Ans- a) Maximum
[B] Short Answers
1) What is thermal energy ?
Ans- Thermal energy is the energy of a body arising from motion of its atoms or molecules. It is directly proportional to the temperature of the substance. It is the measure of average kinetic energy of the particles of the matter and is thus responsible for movement of particles. This movement of particles is called thermal motion.
2) What is hydrogen bonding ?
Ans- Hydrogen bond is found in the molecules in which highly polar N–H, O–H or H–F bonds are present. Although Hydrogen bonding is regarded as being limited To N, O and F; but species such as Cl may Also participate in hydrogen bonding. Energy Of hydrogen bond varies between 10 to 100 kJ mol–1. This is quite a significant amount of energy; therefore, hydrogen bonds are powerful force in determining the structure and properties of many compounds.
3) State Gay Lussac’s law .
Ans- The mathematical Relationship between pressure and Temperature was given by Joseph Gay Lussac And is known as Gay Lussac’s law. It states That at constant volume, pressure of a fixed Amount of a gas varies directly with the Temperature. Mathematically, P ∝T⇒P= constant = k3
T
4) State Charles law .
Ans-Charles’ law, states that Pressure remaining constant, the volume of a fixed mass of a gas is directly Proportional to its absolute temperature. The lowest hypothetical or imaginary Temperature at which gases are supposed to Occupy zero volume is called Absolute zero.
[C] Long Answers
1) State and explain Boyle’s Law .
Ans- On the basis of his experiments, Robert Boyle Reached to the conclusion that at constant Temperature, the pressure of a fixed Amount (i.e., number of moles n) of gas Varies inversely with its volume. This is Known as Boyle’s law. Mathematically, it can Be written as p ∝1⇒p =k11
V V
Where k1 Is the proportionality constant. The Value of constant k1 Depends upon the Amount of the gas, temperature of the gas And the units in which p and V are expressed. On rearranging equation we obtain pV = k1 .It means that at constant temperature,product of pressure and volume of a fixedamount of gas is constant.If a fixed amount of gas at constant temperature T occupying volume V1 at pressure P1 undergoes expansion, so that volume becomes V2 and pressure becomes P2 , Then according to Boyle’s law : P1V1 = P2V2 = constant ⇒P1= V2
P2. V1.
2) Write physical Properties of gaseous .
Ans-The gaseous state is characterized by the following physical properties.
- Gases are highly compressible.
- Gases exert pressure equally in all
- Gases have much lower density than the Solids and liquids.
- The volume and the shape of gases are Not fixed. These assume volume and shape of the container.
- Gases mix evenly and completely in all Proportions without any mechanical aid.
Case –III
First complete data on pressure-volume-Temperature relations of a substance in bothGaseous and liquid state was obtained byThomas Andrews on Carbon dioxide. He plottedIsotherms of carbon dioxide at variousTemperatures . Later on it was foundThat real gases behave in the same manner asCarbon dioxide. Andrews noticed that at highTemperatures isotherms look like that of anIdeal gas and the gas cannot be liquified even atVery high pressure. As the temperature isLowered, shape of the curve changes and dataShow considerable deviation from idealBehaviour. At 30.98°C carbon dioxide remainsGas upto 73 atmospheric pressure. At 73 atmospheric pressure, liquidCarbon dioxide appears for the first time. TheTemperature 30.98°C is called criticalTemperature (TC) of carbon dioxide. This is theHighest temperature at which liquid carbonDioxide is observed. Above this temperature itIs gas. Volume of one mole of the gas at criticalTemperature is called critical volume (Vc) andPressure at this temperature is called criticalPressure (pC). The critical temperature, pressureand volume are called critical constants. A gasBelow the critical temperature can be liquifiedBy applying pressure, and is called vapour ofThe substance. Carbon dioxide gas below itsCritical temperature is called carbon dioxideVapour.
Intermolecular forces are stronger in liquidState than in gaseous state. Molecules in liquidsAre so close that there is very little empty space between them and under normal conditionsLiquids are denser than gases.Molecules of liquids are held together byAttractive intermolecular forces. Liquids haveDefinite volume because molecules do notSeparate from each other. However, moleculesOf liquids can move past one another freely,Therefore, liquids can flow, can be poured andCan assume the shape of the container in whichThese are stored. If an evacuated container is partially filled withA liquid, a portion of liquid evaporates to fillThe remaining volume of the container withVapour. Initially the liquid evaporates andPressure exerted by vapours on the walls ofThe container (vapour pressure) increases. AfterSome time it becomes constant, an equilibriumIs established between liquid phase andVapour phase. Vapour pressure at this stageIs known as equilibrium vapour pressure orSaturated vapour pressure.. Since process ofVapourisation is temperature dependent; theTemperature must be mentioned whilereporting the vapour pressure of a liquid.
When a liquid is heated in an open vessel,The liquid vapourises from the surface. At theTemperature at which vapour pressure of theLiquid becomes equal to the external pressure,Vapourisation can occur throughout the bulkOf the liquid and vapours expand freely intoThe surroundings. The condition of freeVapourisation throughout the liquid is calledBoiling. The temperature at which vapourPressure of liquid is equal to the externalPressure is called boiling temperature at thatPressure. At 1 atm pressure boilingTemperature is called normal boiling point.If pressure is 1 bar then the boiling point isCalled standard boiling point of the liquid.Standard boiling point of the liquid is slightlyLower than the normal boiling point because 1 bar pressure is slightly less than 1 atmPressure. The normal boiling point of water is100 °C (373 K), its standard boiling point is99.6 °C (372.6 K).At high altitudes atmospheric pressure isLow. Therefore liquids at high altitudes boil atLower temperatures in comparison to that atSea level. Since water boils at low temperatureOn hills, the pressure cooker is used forCooking food. In hospitals surgical instrumentsAre sterilized in autoclaves in which boilingPoint of water is increased by increasing thePressure above the atmospheric pressure byUsing a weight covering the vent.Boiling does not occur when liquid isHeated in a closed vessel. On heatingContinuously vapour pressure increases.
AtFirst a clear boundary is visible between liquidAnd vapour phase because liquid is more denseThan vapour. As the temperature increases more and more molecules go to vapour phaseAnd density of vapours rises. At the same timeLiquid becomes less dense. It expands becauseMolecules move apart. When density of liquidAnd vapours becomes the same; the clearBoundary between liquid and vapoursDisappears. This temperature is called critical Temperature.
[A] MCQ
1) First complete data on Pressure-Volume-Temperature relations of a substance in both Gaseous and liquid state was obtained by …
(a) Thomas Andrews
(b) Fritz London
(c) Robert Boyle
(d) Joseph Lewis Gay Lussac
Ans-a) Thomas Andrews
2) Critical Temperature (TC) of carbon dioxide is …
(a) 24°C
(b) 8°C
(c) 56°C
(d) 29°C
Ans- b) 30.8°C
3) The condition of free Vapourisation throughout the liquid is called …
(a) Evaporation
(b) Melting
(c) Boiling
(d) None of above
Ans- c) Boiling
4) Standard boiling point of Water is …
(a) 100°C
(b) 3°C
(c) 105°C
(d) 6 °C
Ans- d) 99.6 °C.
5) Boundary between liquid and vapours Disappears ,This temperature is called …
(a) Critical temperature
(b) Absolute temperature
(c) Normal temperature
(d) Boiling temperature
Ans- a) Critical temperature
[B] Short Answers
1) Why liquids can flow, can be poured and can assume the shape of the container in which these are stored?
Ans- Molecules of liquids are held together byAttractive intermolecular forces. Liquids have 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.
2) Explain equilibrium vapour pressure orsaturated vapour pressure.
Ans- The liquid evaporates and Pressure exerted by vapours on the walls of The container (vapour pressure) increases. After Some time it becomes constant, an equilibrium Is established between liquid phase and Vapour phase. Vapour pressure at this stage Is known as equilibrium vapour pressure or Saturated vapour pressure.
3) Define
(i) Boiling Temperature
(ii) Standard boiling point
(iii) Normal Boiling Point
Ans- i.) The temperature at which vapour pressure of liquid is equal to the external Pressure is called boiling temperature at that pressure.
ii.) If pressure is 1 bar then the boiling point is calledstandard boiling point of the liquid.
iii.) At 1 atm pressure boiling temperature is called normal boiling point.
[C] Long Answers
1) Explain Andrew’s Isotherms of Carbon dioxide
Ans- First complete data on pressure-volume-Temperature relations of a substance in both Gaseous and liquid state was obtained by Thomas Andrews on Carbon dioxide. He plotted Isotherms of carbon dioxide at various Temperatures . Later on it was found That real gases behave in the same manner as Carbon dioxide. Andrews noticed that at high Temperatures isotherms look like that of an Ideal gas and the gas cannot be liquified even at Very high pressure. As the temperature is Lowered, shape of the curve changes and data Show considerable deviation from ideal Behaviour. At 30.98°C carbon dioxide remains Gas upto 73 atmospheric pressure. At 73 atmospheric pressure, liquid Carbon dioxide appears for the first time. The Temperature 30.98°C is called critical Temperature (TC ) of carbon dioxide. This is the Highest temperature at which liquid carbon Dioxide is observed.
Part – IV
It is well known fact that liquids assume theshape of the container. Why is it then smalldrops of mercury form spherical bead insteadof spreading on the surface. Why do particlesof soil at the bottom of river remain separatedbut they stick together when taken out ? Whydoes a liquid rise (or fall) in a thin capillary assoon as the capillary touches the surface ofthe liquid ? All these phenomena are causeddue to the characteristic property of liquids,called surface tension. A molecule in the bulkof liquid experiences equal intermolecularforces from all sides. The molecule, thereforedoes not experience any net force. But for themolecule on the surface of liquid, net attractiveforce is towards the interior of the liquid, due to the molecules below it. Since thereare no molecules above it.Liquids tend to minimize their surface area.The molecules on the surface experience a netdownward force and have more energy than the molecules in the bulk, which do notexperience any net force. Therefore, liquids tendto have minimum number of molecules at theirsurface. If surface of the liquid is increased bypulling a molecule from the bulk, attractiveforces will have to be overcome. This willrequire expenditure of energy. The energyrequired to increase the surface area of theliquid by one unit is defined as surface energy.Its dimensions are J m –2. Surface tension isdefined as the force acting per unit lengthperpendicular to the line drawn on the surfaceof liquid. It is denoted by Greek letter γ(Gamma). It has dimensions of kg s –2 and in SIunit it is expressed as N m –1.
The lowest energystate of the liquid will be when surface area isminimum. Liquid tends to rise (or fall) in the capillarybecause of surface tension. Liquids wet thethings because they spread across their surfacesas thin film. Moist soil grains are pulled togetherbecause surface area of thin film of water isreduced. It is surface tension which givesstretching property to the surface of a liquid.On flat surface, droplets are slightly flattenedby the effect of gravity; but in the gravity freeenvironments drops are perfectly spherical. Viscosity is a measure of resistance toflow which arises due to the internal frictionbetween layers of fluid as they slip past oneanother while liquid flows. Strongintermolecular forces between molecules holdthem together and resist movement of layerspast one another.
When a liquid flows over a fixed surface,the layer of molecules in the immediate contactof surface is stationary. The velocity of upperlayers increases as the distance of layers fromthe fixed layer increases. This type of flow inwhich there is a regular gradation of velocityin passing from one layer to the next is calledlaminar flow.‘ η’ is proportionality constant and is calledcoefficient of viscosity. Viscosity coefficientis the force when velocity gradient is unity andthe area of contact is unit area. Thus ‘ η’ ismeasure of viscosity. SI unit of viscositycoefficient is 1 newton second per square metre(N s m–2) = pascal second (Pa s =1 g cm–1s –1). Incgs system the unit of coefficient of viscosity ispoise (named after great scientist Jean LouisePoiseuille).1 poise = 1 g cm–1s –1 = 10 –1kg m –1s –1Greater the viscosity, the more slowly theliquid flows. Hydrogen bonding and van derWaals forces are strong enough to cause highviscosity.
Glass is an extremely viscous liquid.It is so viscous that many of its propertiesresemble solids.Viscosity of liquids decreases as thetemperature rises because at high temperaturemolecules have high kinetic energy and canovercome the intermolecular forces to slip pastone another between the layers.
[A] MCQ
1) The dimension of surface energy is …
(a) J m–2
(b) J m2
(c) Kjm–2
(d) Kjm2
Ans- a) J m–2
2) 1 poise =
(a) 1 cmskg-1
(b) 1 g cm–1s –1
(c) 1 g cms –1
(d) 1 g cm–1s
Ans- b) 1 g cm–1s –1
3) Which of the following is most viscous liquid ?
(a) Glass
(b) Water
(c) Mercury
(d) Kerosene
Ans- a) Glass
4) Surface Tension denoteed by greek letter …
(a) ε
(b) ζ
(c) δ
(d) γ
Ans- d) γ
5) Flow in which there is a regular gradation of velocity in passing from one layer to the next is called …
(a) Turbulent flow
(b) Shear flow
(c) Streamline flow
(d) laminar flow.
Ans- d) laminar flow.
[B] Short Answers
1) What is laminar flow ?
Ans- When a liquid flows over a fixed surface, the layer of molecules in the immediate contact of surface is stationary. The velocity of upper layers increases as the distance of layers from the fixed layer increases. This type of flow in which there is a regular gradation of velocity in passing from one layer to the next is called laminar flow.
2) What is viscosity coefficient ?
Ans- Viscosity coefficient is the force when velocity gradient is unity and the area of contact is unit area. Thus ‘ η’ is measure of viscosity. SI unit of viscosity coefficient is 1 newton second per square metre (N s m–2) = pascal second (Pa s =1 g cm–1s –1).
3) What is viscosity ?
Ans- Viscosity is a measure of resistance to flow which arises due to the internal friction between layers of fluid as they slip past oneanother while liquid flows. Strongintermolecular forces between molecules holdthem together and resist movement of layerspast one another.
[C] Long Answers
1) Explain surface tension ?
Ans- Surface tension is the characteristic property of liquids. A molecule in the bulk of liquid experiences equal intermolecular forces from all sides. The molecule, therefore does not experience any net force. But for the molecule on the surface of liquid, net attractive force is towards the interior of the liquid, due to the molecules below it. Since there are no molecules above it. Liquids tend to minimize their surface area. The molecules on the surface experience a net downward force and have more energy than the molecules in the bulk, which do not experience any net force. Therefore, liquids tend to have minimum number of molecules at their surface. If surface of the liquid is increased by pulling a molecule from the bulk, attractive forces will have to be overcome.
2) ‘The lowest energy state of the liquid will be when surface area is minimum and Spherical shape satisfies this condition’. explain the statement with suitable examples.
Ans-The lowest energy state of the liquid will be when surface area is minimum. Liquid tends to rise (or fall) in the capillary because of surface tension. Liquids wet the things because they spread across their surfaces as thin film. Moist soil grains are pulled together because surface area of thin film of water is reduced. It is surface tension which gives stretching property to the surface of a liquid. On flat surface, droplets are slightly flattened by the effect of gravity; but in the gravity free environments drops are perfectly spherical.
Case Study States of Matter Class 11