Model Test Questions Chemistry Test # 11 for Chapter # 5 (Physical States of States)
Short Answer-Questions
Q1. What is KMT? Give its main postulates with respect to three states of matter. Or How kinetic molecular theory differentiates states of matter?
Q2. Define Boiling Point, Melting Point, Freezing Point, fusion, absolute zero
Q3. What is the difference between evaporation and boiling? What is boiling point? How liquid is converted to gas?
Q4. What is diffusion? Why gases diffuse rapidly, Explain? State Graham’s law of diffusion of gases. Which gas from among CO2, CH4 and H2 will diffuse the fastest and why? Give the reason
Q5. Why density of gases increases on cooling?
Q6.Explain that Effusion depends on mean free path.
Q7. Which variables are kept constant in Boyle's law?
Q8. When a gas is allowed to expand, what will be the effect on its temperature?
Q9. What is pressure? Give its reason and unit.
Q10. Can you reduce temperature of a gas by increasing its volume?
Q11.Explain how evaporation caused a cooling effect?
Q12. What is density, how the density of liquid is affected by temperature and pressure?
Q13. What is Effusion, explain with the examples?
Q14. Discuss the property of evaporation in liquids? Which factors affects the evaporation process?
Q15. Why increase in temperature causes increase in the process of evaporation?
Q16. Describe the process of diffusion in liquids? Why rate of diffusion in liquids is less than gases? Prove with the help of examples. State the factors which influence it?
Q17. Define the allotropy with examples?
Long Answer-Questions
Q1. Define vapour pressure and justify that it is visible in a close system only? How equilibrium state involved in vapour pressure of liquids in close system?
Q2. How boiling point is affected by different factors? How boiling point of a substance is affected by atmospheric pressure?
Q3. Describe the Boyle's law with example?
Q4. Define and explain the Charles' law of gases
Q5. Differentiate between amorphous and Crystalline Solids?
Q6. Explain plasma with the daily life examples?
Q7.Justify that atoms of Bose Einstein condensate are super unexcited and super cooled?
Numericals
Q1. Convert the following units :
(A) 100oC to K
(b) 150oC to K
(c) 780K to oC
(d) 170 K to oC
Q2. It is desired to increase the volume of a fixed amount of gas from 90.5 to 120 cm3 while holding the pressure constant. What would be the final temperature if initial temperature is 33oC.
Q3. A 78 ml sample of gas is heated from 35°C to 80°C at constant pressure. What is the final volume?
Q4. A gas occupies a volume of 40.0 dm3 at standard temperature (0oC) and pressure (1 atm), when pressure is increased up to 3 atm unchanged temperature what would be the new volume?
Q5. The pressure of a sample gas is 8 atm and the volume is 15 liters. If the pressure is reduced to 6 atm, what is the volume?
Q6. The 800 cm3 of a gas is enclosed in a container under a pressure of 750 mm. If the volume is reduced to 250 cm3, what will be the pressure?
Q7. The pressure of a sample gas is 3 atm and the volume is 5 liters. If the pressure is reduced to 2 atm, what will be the new volume? (7.5 liters.)
Q8. The 700 cm3 of a gas is enclosed in a container under a pressure of 650 mm of Hg. If the volume is reduced to 350 cm3 , what will be the pressure then? (1300 mm Hg)
Q9. A 600 ml sample of gas is heated from 27 °C to 77 °C at constant pressure. What is the final volume? (700 ml)
Q10. A sample of Hydrogen gas has a volume of 350 cm3 at 40 C. If gas is allowed to expand up to 700 cm3 at constant pressure. Find out its final temperature? (626 K)
Answers of Short Questions
Q1. What is KMT? Give its main postulates with respect to three states of matter. Or How kinetic molecular theory differentiates states of matter?
Answer
Definition
Boltzmann, Maxwell, Kelvin put forward kinetic molecular theory.
Kinetic molecular theory is a hypothetical but practical model which explains the general structures, composition and properties of all the three states of matter.
According to K.M.T, all matter is composed of extremely tiny particles called molecules which are always in a state of continuous random motion possessing kinetic energy. The three states of matter depend upon the arrangements, motions and forces of attraction between these particles.
Postulate of Kinetic Molecular Theory for GASEOUS State
1. The molecular are widely separated from each other.
2. The molecules have negligible volume.
3. The gas molecules are in constant random motion
4. The gas molecules move in straight line until they collide with each other or wall of container
5. The collisions of gas molecular are elastic in nature as during collision molecules do not lose energy
6. Pressure produced when molecules collide with the wall of container
7. There are attractive and repulsive forces been molecules.
Postulate of Kinetic Molecular Theory for Liquid State
According to their kinetic molecular theory liquid state shows following characteristics.
1. The molecules of a liquid are randomly arranged like gases.
2. The molecules of liquids have less kinetic energy than gases.
3. The molecules of liquids are fairly free to move.
4. The Liquids has no definite shape but assumes the shape of container.
5. The Boiling point of liquids depends on the external atmospheric pressure.
6. The Liquids are denser and not compressible like gasses.
Comparison of Three States of Matter according to KMT
Q2. Define Boiling Point, Melting Point, Freezing Point, fusion, absolute zero
Answer
Boiling Point
The temperature at which vapour pressure of a liquid become equal to atmospheric pressure is called boiling point of the liquid.
Freezing Point
The temperature at which the vapour pressure of a liquid state becomes equal to the vapour pressure of its solid state is known as Freezing Point of a liquid. At this temperature liquid and solid coexist in dynamic equilibrium.
Melting or Fusion
The process of state change from solid to liquid upon heating is called Melting or Fusion which is the characteristic of solids. e.g. change (melting) of ice to water
Melting Point
The temperature at which a solid starts melting on heating at which both liquid and solid phases co-exist at equilibrium is called melting point (m.p.). Melting point is the criteria of purity of solid as a pure solid has a sharp and fixed melting point.
Absolute zero
It is the temperature at which an ideal gas would have zero volume. It is equal to –273°C..
Q3. What is the difference between evaporation and boiling? What is boiling point? How liquid is converted to gas?
Answer
How liquid is converted to gas?
When a liquid changes to gas, the particles absorb heat energy and they start vibrating faster and distance between them increases. On constant vibration, intermolecular forces decrease and particles start moving away from each other and change to gas.
Q4. What is diffusion? Why gases diffuse rapidly, Explain? State Graham’s law of diffusion of gases. Which gas from among CO2, CH4 and H2 will diffuse the fastest and why? Give the reason
Answer
Diffusion
The spontaneous mixing of molecules by random motion and collision to form a homogenous mixture is called diffusion. Diffusion is movement of particles from an area of high concentration to one of low concentration. Diffusion results in the gradual mixing of materials, and eventually it forms a homogeneous mixture.
Reason of Rapid diffusion in gases
Gases are rapidly diffusible due to free movement of molecules.
Graham’s law of diffusion of gases
The quantitative relationship between the rate of diffusion of different gases and their molar masses or densities is called Graham’s Law of Diffusion established by a Scottish chemist, Thomas Graham in 1846. This law states that:
“The rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass (under the same conditions of temperature and pressure).”
Reason of diffusion
According to Graham’s law, lighter gases diffuse faster than heavier gases. e.g. among CO2, CH4 and H2, H2 gas has least molar mass so it diffuses fastest while CO2 has highest molar mass so it diffuses slowest. CH4 has moderate molar mass so it diffuses slowly than H2 but quickly than CO2. The increasing order of rate of diffusion is
CO2 < CH4 < H2
Q5. Why density of gases increases on cooling?
Answer
The density of gases can be increased by cooling as density of gases is inversely proportional to temperature. Greater the temperature, less will be density of gas and vice-versa.
Q6. Explain that Effusion depends on mean free path.
Answer
The Effusion is escaping of gas molecules through a tiny hole into a space with lesser pressure. For process of effusion, the diameter of hole must be smaller than the molecule's mean free path. (Mean free path is the average distance that a gas particle travels between successive collisions with other gas particles).
Q7. Which variables are kept constant in Boyle's law?
Answer
While studying Boyle’s law, temperature and number of moles of a gas are kept constant.
Q8. When a gas is allowed to expand, what will be the effect on its temperature?
Answer
According to Charle’s law, volume of gas is directly proportional to absolute temperature. When a gas is allowed to expand its volume increases which in turn increases its temperature.
Q9. What is pressure? Give its reason and unit.
Answer
Definition of Pressure
Gas Pressure is the force exerted by gaseous molecules per unit area.
Reason of Pressure
Pressure of a gas is due to the elastic collisions of its molecules with the walls of container.
Pressure (P) = Force (F)/Area (A)
Unit of Pressure
The S.I. unit of pressure is N–m–2 which is also known as ‘pascal’ abbreviated as ‘Pa’ (which is defined as the pressure exerted by a force of one newton acting on area of one square meter) i.e. 1 Pa is equal to 1N–m–2
Pressure (P) = Force (F)/Area (A) = N/m2 = 1 Nm–2 = 1Pa (pascal)
Q10. Can you reduce temperature of a gas by increasing its volume?
Answer
Yes. When the gas expands against an external pressure, the gas transfers some energy to the surroundings. and decreases its temperature.
Q11. Explain how evaporation caused a cooling effect?
Answer
The evaporation is also considered as cooling process because when high kinetic energy molecules escape in the air in the form of vapour. The temperature of remaining molecules falls down. To compensate this deficiency of energy molecules absorb energy from the surrounding, due to which temperature of surrounding decreases and feel cold
Q12. What is density, how the density of liquid is affected by temperature and pressure?
Answer
The density of liquid is defined as mass per unit volume.
D = M/V
Factors affecting Density
Temperature
Liquids are less affected by the temperature. By increasing temperature liquids increased their volume which decreases density.
Pressure
Liquids are slightly affected by pressure. Increase in pressure on liquids increases the density but liquids are not readily compressed due to this density change is negligible.
Q13. What is Effusion, explain with the examples?
Answer
Definition
The Effusion is escaping of gas molecules through a tiny hole into a space with lesser pressure.
Effusion depends upon molecular masses of gases. Lighter gases effuse rapidly than heavier gases.
For Example
Q14. Discuss the property of evaporation in liquids? Which factors affects the evaporation process?
Answer
Definition
The process by which a liquid changes to a gas phase is called evaporation. Evaporation is endothermic change in which heat is absorbed.
For example
Clothes dry under the sun due to evaporation in this process water is converted from liquid state into vapours by acquiring from
Reason of Evaporation
The molecules of liquids are in continuous motion they collide with each other but all the molecules do not have same kinetic energy. Majority molecules have average kinetic energy and few have more than average kinetic energy. The molecules having more than average kinetic energy overcome the attractive forces among the molecules and escape from the surface showing evaporation.
Evaporation is a cooling process
The evaporation is also considered as cooling process because when high kinetic energy molecules escape in the air in the form of vapour. The temperature of remaining molecules falls down. To compensate this deficiency of energy molecules absorb energy from the surrounding, due to which temperature of surrounding decreases and feel cold
Factors Affecting Evaporation
(i) Surface Area
The evaporation is a surface based process. Greater the surface area greater is evaporation.
For example water left in bowl evaporate slowly than water left in a large tub. A saucer is used to cool the tea quickly than tea cup.
(ii). Temperature
The rate of evaporation increases with the increase in temperature. Because temperature increases the kinetic molecular energy which overcome the intermolecular forces and makes evaporation rapidly.
For example clothes dry quickly in a sunny day than a cloudy day.
(iii). Intermolecular Forces
The rate of evaporation increases with less intermolecular forces .If intermolecular forces are stronger evaporation is lesser.
For example perfume have lesser intermolecular forces than water therefore they evaporate quickly.
Q15.Why increase in temperature causes increase in the process of evaporation?
Answer
The rate of evaporation increases with the increase in temperature. Because temperature increases the kinetic molecular energy which overcome the intermolecular forces and makes evaporation rapidly.
For example clothes dry quickly in a sunny day than a cloudy day.
Q16. Describe the process of diffusion in liquids? Why rate of diffusion in liquids is less than gases? Prove with the help of examples. State the factors which influence it?
Answer
Definition of Diffusion
The diffusion is spreading out of the liquid molecules throughout the vessel.
Like gases, liquids are able to diffuse as their molecules are also able to move and flow.
Diffusion in liquids is much slower than that of gases as the rate of movement of liquid molecules is smaller than gases.
As the molecule of liquid are in cluster and bounded with strong intermolecular binding forces. The liquid molecules are in continuous motion. They move from high concentration to low concentration and mix up with molecules of others liquids from homogenous mixture.
For example a drop of dye or any coloured solution like blue ink diffuses through water.
Factors affecting Diffusion
Intermolecular forces
Liquids have weaker intermolecular forces than solid due to this liquids diffuse faster than solid but less rapidly than gases.
Size of molecules
Diffusion depends upon size of molecules. Small size molecules diffuse rapidly than bigger one.
For example, water diffuses slowly than alcohol.
Shape of molecules
Molecules with irregular shape diffuse slowly than regular shaped molecules because they easily slip over and move faster.
Temperature
Diffusion increases by increasing temperature because at high temperature intermolecular forces become weak due to high kinetic energy of the molecules.
Q17.Define the allotropy with examples?
Answer
Definition
The existence of an element in more than one crystalline forms is known as allotropy. These forms of the element are called allotropes or allotropic forms.
Reason of Allotropy
This happens when the atoms of the element are bonded together in a different way. Different bonding arrangements between atoms result in different structures with different chemical and physical properties.
Examples
Only some elements like sulphur, phosphorus, carbon and tin are elements which show allotropy.
For example, the allotropes of carbon include:
(i) Diamond, where the carbon atoms are bonded together in a four-cornered lattice arrangement
(ii) Graphite, where the carbon atoms are bonded together in sheets of a six-sided lattice.
(iii) Graphene, single sheet of graphite.
(iv) Fullerenes, where the carbon atoms are bonded together in spheres, cylinders or egg-shaped
Long Answer-Questions
Q1. Define vapour pressure and justify that it is visible in a close system only? How equilibrium state involved in vapour pressure of liquids in close system?
Answer
Definition
The pressure exerted by vapours in equilibrium with its pure liquid at a particular temperature is called Vapour Pressure.
The equilibrium is a state when rate of evaporation is equal to rate of condensation but in opposite directions.
Explanation or Origin of Vapour Pressure
Vapour pressure takes place in a closed system because in open system or open surface liquid molecule evaporates and mix-up with air.
Evaporated molecules start gathering over the liquid surface. Initially the vapour condense slowly to return to liquid .After sometimes condensation process increases and a stage reaches when the rate of evaporation become equal to rate of condensation. At that stage the number of molecules evaporates will be equal to the number of molecules condensate (coming back) to liquid. At this point where pressure exerted by the vapour is called vapour pressure.
Unit
The unit of pressure is expressed in mm of Hg, atmosphere, torr or newton per meter square.
Factors Affecting Vapour Pressure
(i). Nature of Liquid
The vapour pressure depends upon the nature of liquids .Polar liquids have low vapour pressure than nonpolar liquids at the same temperature. It is because of strong intermolecular forces of molecules and high boiling point in the polar liquids.
For example
Water (polar liquid) has less vapour pressure than alcohol (non-polar liquid).
(ii). Size of Molecules
The vapour pressure is more in small size molecules because small sized molecules evaporate easily and exert more vapour pressure.
For example
Hexane (C6H14) has a small size molecule as compared to decane (C10H22), due to this hexane evaporate rapidly and exert more pressure.
(iii). Temperature
The vapour pressure increases with raise in temperature. The average kinetic energy of molecules increases with temperature which causes increase in vapour pressure.
For example
Vapour pressure of water at 0°C is 4.58 mm Hg while at 100°C it increases up to 760mm Hg.
Q3. Describe the Boyle's law with example?
Answer
Boyle's Law/ Pressure-Volume Law
Statement
A characteristic property of gases is their great compressibility. The relationship between pressure and volume of gases is known as Boyle’s law given by Robert Boyle In 1662.
Providing temperature constant, the volume of a fixed mass of a gas is inversely proportional to its pressure. OR The product of pressure and volume of a given mass of a gas at constant temperature is always constant.
Mathematical Expression of Boyle’s Law
V a 1/P (Temperature constant)
V = K x 1/P (Removing proportionality sign (a) by introducing a constant)
PV = K (Constant )
Here K = Constant of proportionality whose value depends upon the amount of the gas, temperature of the gas and the units in which p and V are expressed.]
If, pressure is changed from P1 to P2, the volume will change from V1 to V2, then according to Boyle’s law:
P1V1 = K ––––––––– (1), And
P2V2 = K –––––––––– (2) [Comparing equation (1) and (2).]
P1V1 = P2V2 = K [This is the second form of Boyle’s law]
Where
P1 = initial pressure,
P2 = final pressure,
V1 = initial volume,
V2 = final volume
Experimental Verification
The relationship between volume and pressure at constant temperature is shown in the following figure. Where given mass of a gas at constant temperature shows increase in volume by decrease in pressure. While increase in pressure decreases volume. But in both cases, the product of pressure and volume is constant.
Q4. Define and explain the Charles' law of gases
Answer
Charle’s Law (Effect of Absolute Temperature on Gas Volume)
Statement
In 1787, French physicist Jacques Charles proposed his law to explain the relationship between volume and temperature keeping the pressure constant.
The volume of a fixed mass of a gas held at constant pressure is directly proportional to the absolute (kelvin) temperature. In other words, the ratio of volume of a fixed mass (mole) gas to its absolute temperature at constant pressure always remains constant.
Mathematical Expression
Then, Charles law can be expressed as:
V a T (Pressure constant)
V = KT (Removing proportionality sign by introducing a constant)
V/T = Constant = K [Here K = Constant of proportionality]
If V1 and V2 are the original and changed volume; T1 and T2 are the original and changed temperature, then
V1/T1 = K ---------------------- (1) And
V2/T2 = K ---------------------- (2)
(Comparing equation (1) and (2), we get the second form of Charle’s law)
V1/T1 = V2/T2 = K
Absolute Temperature Scale
Lord Kelvin introduced absolute temperature scale or Kelvin scale. It starts from zero, 0K which is equal to –273°C. It is the temperature at which an ideal gas would have zero volume and known as absolute zero. As Celsius and kelvin scales have equal degree range therefore when zero kelvin is equal to -273°C, and 273 kelvin is equal to zero °C.
Conversion of kelvin temperature and Celsius temperature are vice versa as follows:
K = °C + 273 And °C = K – 273
Experimental Verification
According to Charele’s law if absolute temperature of a gas is doubled, its volume will also double. For example, that if you double the temperature from 300 K to 600 K, at constant pressure, the volume of a fixed mass of the gas will become double
Q6. Differentiate between amorphous and Crystalline Solids?
Answer
Difference between Amorphous and Crystalline Solids
Answer
English scientist William Crookes identify the fourth states of matter known as Plasma.
Plasma are super-hot and super excited atoms. Plasma is distinct state of matter containing a significant number of electrically charged particles which affect its electrical properties and behavior.
It was discovered by adding energy to a gas. As a result some electrons left their atoms and formed positive and negative ions by ionization. In plasma these charged particles react strongly to electric and magnetic fields. If plasma loses heat, the ions will re-form into a gas, emitting the energy which had caused them to ionize.
Some examples of daily life are as follow:
(i) The lightning makes plasma naturally.
(ii) The Artificial (man-made) uses of plasma include fluorescent light bulbs, Neon signs.
(iii) The use of plasma display of television or computer screens.
(iv) The plasma lamps and globes are popular in children's toys and room decoration.
Scientists are experimenting with plasma to make a new kind of nuclear power, called fusion, which will be much better and safer than ordinary nuclear power with less radioactive waste.
Q8. Justify that atoms of Bose Einstein condensate are super unexcited and super cooled?
Answer
The atoms in a Bose-Einstein condensate (BEC) are super unexcited and super cold atoms.
Two scientists Satyendra Bose and Albert Einstein discovered another state of matter in 1920 but they did not have the equipment and facilities to make it happens at that time.
Afterward in 1995 two other scientists Eric Cornell and Carl Weiman also proposed another state of matter known as Bose-Einstein Condensate (BEC)
They discovered that as plasma are super-hot and super excited atoms. The atoms in a Bose-Einstein condensate (BEC) are totally opposite. They are super unexcited and super cold atoms.
Condensation happens when several gas molecules come together and form a liquid. It all happens because of a loss of energy. Gases are really excited or energetic atoms. When they lose energy, they slow down and begin to gather. They can gather into one drop.
For example, when you boil water. Water vapour in the form of steam condenses on the lid of pot. Vapour cool and become a liquid again. You would then have a condensate. (Absolute Zero is a temperature where all the atomic activities stop theoretically).
The BEC happens at super low temperatures. When we get a temperature near absolute zero, all molecular motion stops due to depletion of energy, and atoms begin to clump.
The result of this clumping is the BEC. In common we cannot see this state in observable nature, because it is very difficult to reach at very low temperature under normal lab conditions.
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