Plus One Chemistry Notes Chapter 5 States of Matter is part of Plus One Chemistry Notes. Here we have given Kerala Plus One Chemistry Notes Chapter 5 States of Matter.
|Text Book||NCERT Based|
|Chapter Name||States of Matter|
|Category||Plus One Kerala|
Kerala Plus One Chemistry Notes Chapter 5 States of Matter
The observable characteristics of chemical systems represent bulk properties of matter. Chemical properties do not depend on the physical state of matter but chemical reactions do.
These are the forces of attraction and repulsion between interacting particles or atoms or molecules.
1. van der Waal’s forces
These are very short live intermolecular attractive forces. These forces exist between all atoms and molecules when they approach each other quite closely.
2. Dispersion forces or London forces
The force of attraction between two temporary dipoles is known as London forces. These include non-polar molecules which have no dipole moment and lie at short distance 500 pm.
3. Dipole-dipole forces
These type of interactions occur in polar molecules having permanent dipoles such as HCI, HBr, H2S etc. Such molecules possess partial charges of opposite sign at their ends. The positive end of one molecule attracts the negative end of the other molecule and vice versa.
4. Dipole-induced dipole forces
These type of interactions are found in a mixture, containing polar and non-polar molecules. When a non-polar molecule is brought near a polar molecule, the positive end of the polar molecule attracts the electron cloud at the non polar molecule. Thus a polarity is induced in the non-polar molecule. Then there will be attractive interaction between the polar molecule and the induced dipole of the non polar molecule
5. Hydrogen bond
The bond between the hydrogen atom of one molecule and the more electronegative atom of the same or another molecule is called hydrogen bond. This is found in highly polar bonds and in dipole-dipole interaction.
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.
Inter molecular forces Vs Thermal interactions
The three spates of matter are inter convertible. This can be done by heating (increases K.E) or cooling, ie., balance between the inter molecular forces and the thermal energy of the molecules.
The Gaseous State
- Gases are highly compressible.
- Gases exert pressure equally in all directions.
- 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 with out any mechanical aid.
The Gas Laws
The four measurable properties (mass, volume, pressure and temperature) of a gas are inter related and these relationship are commonly known as gas laws.
Boyle’s law pressure-Volume Relationship)
The law states that at constant temperture, the pressure (volume) of a fixed mass of gas is inversely proportional to the volume (pressure).
Pα at constant temp and number of moles. Also, V α at constant temp and number of moles PV = a constant
The value of the constant depends upon the amount and temperature of the Gas. P1V1 = a constant or P1V1= P2V2 = a constant.
Applications of Boyle’s law
According to Boyle’s law, for a certain fixed amount of gas PV = a constant or P1V1= P2V2= P3V3 and so on.
Some applications are:
- It is used in cycle pump.
- It is used in aneriod barometer.
- It is used in tyre pressure gauze.
Charles’ law (Temperature-Volume relationship)
This law states that the volume of a given mass of a gas at constant pressure is directly proportional to the absolute temperature.
V α T at constant P. i.e., V = kT where A is a constant or = a constant. .
Note: Charles’law can also be stated as the volume of fixed mass of gas at constant pressure increases or decreases by 1/273 of its volume. It is obeyed by ideal gases but other gases obey this law at very low pressure and high temperature.
If volume of the gas at 0 °e and t °C are V0 and V1 respectively then,
Absolute zero and Absolute scale of temperature
The lowest possible temperature at which all the gases are supposed to occupy zero volume is called absolute zero . The temperature at which volume become zero has been found to be -273.15 °C is known as the absolute scale of temperature.
Gay Lussac’s Law (Pressure- Temperature Relationship)
The 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 α T or = constant
This relationship can be derived from Boyle’s law and Charles’ law. Each line the Pressure vs temperature (Kelvin) graph at constant molar volume is called isochore.
It states that equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules. Mathematically we can write V α Nat constant T and P.
The number of molecules in one mole of a gas has been determined to be 6.022 x 1023 and is known as Avogadro’s constant. A gas that follows Boyle’s law, Charles’ law and Avagadro’s law strictly is called an ideal gas .
Standard Temperature and Pressure
• Standard temperature = 273.15 K (Freezing temperature of water) or 0 °C.
• Standard pressure = 1 atm.
• Standard volume = 22.4 L
Ideal Gas Equation
A gas which obeys Boyle’s and Charles’ law under all conditions of T and P is called ideal gas. Other gases will follow ideal gas equation at high T and low P.
A vessel of 120 ml capacity contains a certain amount of gas at 35°C and 1.2 bar pressure. The gas is transferred to another vessel of volume 180 ml at 35°C. What would be its pressure?
A sample of helium has a volume of 500 cm3 at 373 K. Calculate the temperature at which the volume will become 260 cm3 keeping pressure constant.
A sample N2 gas has volume of 1.00 L at a pressure of 0.50 atm at 4 PC. Calculate the pressure if the gas is compressed to 0.225 cm3 at -6°C.
Density and Molar Mass of a Gaseous Substance
Ideal gas equation can be rearranged as follows:
On rearranging equation we get the relationship for calculating molar mass of a gas.
Dalton’s law of Partial pressure
It states that total pressure exerted by the mixture of non-reactive gases enclosed in a definite volume is equal to the sum of the partial pressures of individual gases.
Ptotal = P1 + P2 + P3 + … at constant Temp, Vol.
Application of Dalton’s Law of Partial Pressures
1. In the determination of pressure of a dry gas.
Pdry gas= Ptotal -Aqueous tension.
Aqueous tension: Pressure exerted by saturated water vapours is called aqueous tension.
2. To calculate the partial pressure in terms of mole fraction: Suppose at temperature T, three gases enclosed in the volume V, exert partial pressures P1 P2 P3 .
Kinetic Molecular Theory of Gases
Maxwell, Boltzmann and others put forward a theoretical model of the gas. The theory is
known as kinetic molecular theory of gases or microcopic model of gases.
Postulates of kinetic molecular theory are:
- All gases are made up of a large number of extremely small particles called molecules.
- The molecules are separated from one another by large distances so that the actual volume of the molecules is negligible as compared to the total volume of gas.
- The molecules are in a state of continuous rapid motion in all directions. During their motion, they keep on colliding with one another and also with the walls of the container.
- Molecular collisions are perfectly elastic i.e, there is no net loss or gain of energy in their collisions. However, there may be redistribution of energy during such collisions.
- There are no attractive forces between the molecules. The move completely independent of each other.
Deviation from Ideal Behavoiur
It is apparent that at very high pressure the measured volume is more than the calculated volume. At low pressure, measured and calculated volumes approach each other.
It is found that real gases do not follow Boyle’s law, Charles’ law and Avogadro’s law perfectly under all conditions.
Compressibility factor (Z)
The deviation from ideal behaviour is measured in terms of compressibility factor Z, which is the ratio of product PV and nRT.
Boyle temperature or Boyle point
The temperature at which a real gas obeys ideal gas law over an appreciable range of pressure is called Boyle temperature or Boyle point.
Liquifaction of Gases
The highest temperature of which liquifaction of the gas first occurs is called critical temperature (Tc). Volume of one mole of the gas at critical temperature is called critical volume (Vc) and pressure at this temperature is called critical pressure (Pc).
The critical temperature, pressure and volume are called critical constants.
The Liquid State
The liquid state lies between the gaseous and solid states. In liquids, the cohesive forces between the particles are strong enough to keep them together.
Vapour pressure of the Liquid (Equilibrium or Saturated vapour pressure)
The pressure exerted by the vapours in equilibrium with the liquid at a given temperature is called vapour pressure of the liquid. For any liquid, the vapour pressure increases with increase in temperature.
Surface Tension (S.T)
Surface tension of a liquid is the amount of work that must be done to expand the surface of liquid by unit area.
- It is due to S.T. that a drop of liquid assumes spherical shape because the surface area of a sphere is minimum.
- T. is also responsible for the rise or fall in liquids in capillary tube.
- A shaving blade or a thin metallic needle floats on the surface of water due to S.T.
It is a common observation that certain liquids flow faster than others. For example, liquid like water, ether etc. flow rapidly while liquids like glycerine, castor oil, honey etc. flow slowly. These differences in flow rates result from a property known as viscosity. Every liquid has some internal resistance to flow. This internal resistance to flow possessed by a liquid is called its viscosity. Liquids which flow slowly have high internal resistance and are said to have high viscosity. On the other hand, liquids which flow rapidly have low internal resistance and are said to have low viscosity.
What is the effect of temperature on viscosity and why ?
Viscosity increases with the decrease in temperature because inter molecular force of attraction increases.
Kinetic energy and Molecular speeds
Molecules of gases remain in continuous motion. If there are n number of molecules in a sample and their individual speeds are u1, u2, u3………. un then average speed of molecules uav can be calculated as follows:
Maxwell and Boltzmann have shown that actual distribution of molecular speeds depends on temperature and molecular mass of a gas.
The maximum in the curve represents speed possessed by maximum number of molecules. This speed is called most probable speed,uamp.
We know that kinetic energy of a particle is given by the expression:
Kinetic energy 1/2 mu2
Therefore, if we want to know average translational kinetic energy, , for the movement of a gas particle in a straight line, we require the value of mean of square of speeds, ;, of all molecules.
Root mean square velocity (ums). It is defined as the square root of the mean (average) of the squares of velocity of all the molecules. It is a direct measure of average kinetic energy of the molecules
where u1is velocity of n1 molecules u2 is velocity of n2 molecules and so on. un is velocity of nn molecules
[Here, R is gas constant.T is temperature in Kelvin, M is molar mass of gas]
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