Important Definitions Class 11 Term-2

 

Important Definitions Term-2

 

Unit 5-State of Matter

 

Intermolecular Forces: The force of attraction existing among the molecules of a substance (gaseous, liquid or solid) are called intermolecular forces.

Thermal Energy: Thermal energy is the energy of a body arising from motion of its atoms and molecules.

Boyle’s law: Boyle’s law states that at constant temperature, the pressure of a fixed amount of a gas is inversely proportional to its volume.

Mathematically,

 P 𝜶 1 / V

P = k / V

Where, P is the pressure of gas, V is the Volume of gas and k is the proportionality constant.

Isotherm: The P-V curve at constant temperature is termed as isotherm.

Charles’ Law: Charles’ law states that at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.

Mathematically,

V α T

V = k T

Where, V is the volume of gas, T is the absolute temperature and k is the proportionality constant.

Isobar: The V-T curve at constant pressure is termed as isobar.

Absolute zero: The lowest possible hypothetical or theoretical temperature of -273⁰C at which a gas is supposed to have zero volume is called Absolute zero.

Gay-Lussac’s Law/Amonton’s Law: It states that at constant volume, pressure of a fixed amount of gas is directly proportional to its temperature.

Mathematically,

P α T

P = k T

Where, P is the pressure of gas, T is the absolute temperature and k is the proportionality constant.

Isochore: The P-T curve at constant volume is termed as isochore.

Avogadro’s Law: It states that equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules.

Mathematically,

V α n

V = k n

Where, V is the volume of gas, n is the number of moles of gas and k is the proportionality constant.

Standard Temperature and Pressure (STP): Standard temperature and pressure means 273.15 K (0°C) temperature and 1 bar (i.e.,exactly 10⁵ pascal)  pressure. These values approximate freezing temperature of water and atmospheric pressure at sea level. At STP molar volume of an ideal gas or a combination of ideal gases is 22.71098 L mol^-.

 

Dalton’s Law of Partial Pressures: It states that the total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases.

Mathematically,

P_Total = P₁+P₂+P₃+……  (at constant T, V)

 

Kinetic Molecular Theory of Gases: The postulates are as follows:

1.     Gases consist of large number of identical particles (atoms or molecules) that are so small and so far apart on the average that the actual volume of the molecules is negligible in comparison to the empty space between them.

2.     There is no force of attraction between the particles of a gas at ordinary temperature and pressure.

3.     Particles of a gas are always in constant and random motion.

4.     Particles of a gas move in all possible directions in straight lines. During their random motion, they collide with each other and with the walls of the container.

5.     Collisions of gas molecules are perfectly elastic. This means that total energy of molecules before and after the collision remains same.

6.     At any particular time, different particles in the gas have different speeds and hence different kinetic energies.

7.     It is assumed that average kinetic energy of the gas molecules is directly proportional to the absolute temperature.

Ideal Gas: A gas which obeys the ideal equation. PV = nRT under all conditions of temperature and pressure is called an ideal gas.

Vander waals equation:

Where, a and b are vander waals constants.

Compressiblity Factor: The deviation from ideal behaviour can be measured in terms of  compressibility factor Z, which is the ratio of product pV and nRT.

Mathematically,

Boyle Temperature: The temperature at which a real gas obeys ideal gas law over an appreciable range of pressure is called Boyle temperature or Boyle point.

 

 

Unit 6-Thermodynamics

 

System: The part of the universe chosen for thermodynamic consideration, (i.e. to study the effect of temperature, pressure etc) is called a system.

Surrounding: The remaining portion of universe, excluding the system is called surrounding.

Open System: A system is said to be an open system if it can exchange both matter and energy with the surroundings.

Closed System: If a system can exchange only energy with the surroundings but not matter, it is called a closed system.

Isolated system: If a system can neither exchange matter nor energy with the surroundings. It is called an isolated system.

State Function: A physical quantity is said to be state function if the change in its value during the process depends only upon initial state and the final state of the system and does not depend upon the path or route by which this change has been brought about. For example: pressure, volume, temperature, internal energy etc.

Extensive properties: These are those properties which depend upon the quantity of the matter contained in the system. For example; mass, volume and heat capacity.

Intensive properties: These are those properties which depend only upon the nature of the substance and are independent of the amount of the substance present in the system. For example; temperature, refractive index, viscosity etc.

Adiabatic process: When a process is carried out in such a manner that no heat can flow from the system to the surroundings or vice versa.

Isothermal process: When a process is carried out in such a manner that the temperature remains constant throughout the process, it is called an isothermal process.

Isochoric process: It is a process during which the volume of the system is kept constant.

Isobaric process: It is a process during which the pressure of the system is kept constant.

First Law of Thermodynamics: Energy can neither be created nor destroyed although it may be converted from one form to another.

or

The total energy of the universe (i.e., the system and the surroundings) remains constant, although it may undergo transformation from one form to the other.

or

The energy of an isolated system is constant.

Heat Capacity, C: Heat capacity of a system is defined as the amount of heat required to raise the temperature of the system through 1⁰C.

Specific Heat Capacity, c: Specific heat capacity of a system is defined as the amount of heat required to raise the temperature of 1 gram of the substance through 1⁰C.

Molar Heat Capacity, C_m: Molar heat capacity of a system is defined as the amount of heat required to raise the temperature of one mole of substance through 1⁰C.

Thermochemical Equations: When a balanced chemical equation not only indicates the quantities of the different reactants and products but also indicates the amount of heat evolved or absorbed (as in the above reactions), it is called a thermochemical equation.

Standard enthalpy of reaction: The standard enthalpy of reaction is the enthalpy change accompanying the reaction when all the reactants and products are taken in their standard states.

Enthalpy of Combustion: The enthalpy of combustion of a substance is defined as the heat change (usually the heat evolved) when 1 mole of substance is completely burnt or oxidized in oxygen. It is usually represented by Δ_cH.

Enthalpy of Formation: The enthalpy of formation of a substance is defined as the heat change, i.e., heat evolved or absorbed when 1 mole of the substance is formed from its elements under given conditions of temperature and pressure. It is usually represented by Δ_fH.

Enthalpy of Solution: The enthalpy of solution of a substance in a particular solvent is defined as the enthalpy change (i.e. amount of heat evolved or absorbed) when 1 mole of the substance is dissolved in a specified amount o fthe solvent.

Enthalpy of atomization: When one mole of a given substance dissociates into gaseous atoms, the enthalpy change accompanying the process is called enthalpy of atomization. It is represented by the symbol Δ_aH.

Enthalpy of Hydration: The amount of enthalpy change (i.e. the heat evolved or absorbed) when one mole of the anhydrous salt combines with the required number of moles of water so as to change into the hydrated salt, is called the enthalpy of hydration or heat of hydration.

Enthalpy of Fusion: Enthalpy of fusion is the enthalpy change accompanying the transformation of one mole of a solid substance into its liquid state at its melting point.

Enthalpy of Vaporisation: It is the amount of heat required to convert one mole of a liquid into its vapour state at its boiling point.

Enthalpy of Sublimation: Enthalpy of sublimation of a substance is the enthalpy change accompanying the conversion of 1 mole of a solid directly into vapour phase at a given temperature below its melting point.

Hess’s Law of Constant Heat Summation: The total amount of heat evolved or absorbed in a reaction is the same whether the reaction takes place in one step ar in a number of steps.

Bond Enthalpy or Bond Energy: Bond energy is the amount of energy released when one mole of bonds are formed from the isolated atoms in the gaseous state or the amount of energy required to dissociate one mole of bonds present between the atoms in the gaseous molecules.

Spontaneous process: A process which can take place by itself or has an urge or tendency to take place is called spontaneous process or to sum up, a spontaneous process is simply a process which is feasible.

Entropy: Entropy is a measure of randomness or disorder of the system.

Second Law of Thermodynamics: The entropy of the universe is continuously increasing.

or

All spontaneous process are thermodynamically irreversible.

or

Without the help of an external agency, a spontaneous process cannot be reversed.

or

All spontaneous process are accompanied by a net increase of entropy, i.e., for all the spontaneous processes, the total entropy change is positive.

Gibbs Free Energy: Gibbs free energy is that thermodynamic quantity of a system the decrease in whose value during a process is equal to the maximum possible useful work that can be obtained from the system.

Third Law of Thermodynamics: The entropy of a perfectly crystalline solid approaches zero as the temperature approaches absolute zero.

or

The entropy of all perfectly crystalline solids may be taken as zero at the absolute zero of temperature.

or

At absolute zero, a perfectly crystalline solid has a perfect order of its constituent particles, i.e., there is no disorder at all. Hence, the absolute entropy is taken as zero.

 

 

Unit 7-Equilibrium

 

Irreversible Reaction: Those reactions which proceed in one direction only and proced almost to completion are called irreversible reaction.

Reversible Reaction: Those reactions which under identical conditions proceed in forward as well as in backward direction and never proceed to completion are called reversible reaction.

Equilibrium: Equilibrium represents the state of a process in which the properties like temperature, pressure, concentration of the system do not show any change with the passage of time. Equilibrium is attained when the rate of forward reaction become equal to the rate of backward reaction.

Henry’s law: It states that the mass of a gas dissolved in a given mass of a solvent at any temperature is proportional to the pressure of the gas above the solvent.

Law of Mass Action: The rate at which a substance reacts is proportional to its active mass and hence the rate of a chemical reaction is proportional to the product of the active masses of the reactants.

Law of Chemical Equilibrium: It may be defined as the product of molar concentrations of the products, each raised to the power equal to its stoichiometric coefficient divided by the product of the molar concentrations of the reactants, each raised to the power equal to its stoichiometric coefficient is constant at constant temperature and is called Equilibrium constant.

Homogeneous Equilibrium: When in an equilibrium reaction, all the reactants and the products are present in the same phase (i.e., gaseous or liquid), it is called a homogeneous equilibrium.

Heterogeneous Equilibrium: When in an equilibrium reaction, all the reactants and the products are present in two or more than two phases, it is called a homogeneous equilibrium.

Le Chatelier’s Principle: It states that a change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner so as to reduce or to counteract the effect of the change.

Electrolyte: An electrolyte is defined as a compound whose aqueous solution or melt conducts electricity.

Strong Electrolyte: A strong electrolyte is defined as a substance which dissociates almost completely into ions in aqueous solution and hence is a very good conductor of electricity. e.g. KOH, HCl, NaCl etc.

Weak Electrolyte: A weak electrolyte is defined as a substance which dissociates to a small extent in aqueous solution and hence conducts electricity also to a small extent, e.g. CH₃COOH, NH₄OH.

Arrhenius Concept of Acids and Bases:

Acid: An acid is a substance which when dissolved into water gives hydrogen ions (H⁺).

Base: A base is a substance which when dissolved into water gives hydroxide ions (OH^-).

Bronsted-Lowry Concept of Acids and Bases:

Acids: An acid is defined as a substance which has the tendency to give a proton (H⁺).

Base: A base is defined as a substance which has a tendency to accept a proton (H⁺).

Lewis Concept of Acids and Bases:

Acid: An acid is defined as substance (atom, ion or molecule) which is capable of accepting a pair of electrons.

Base: A base is defined as a substance (atom, ion or molecule) which is capable of donating an unshared (lone) pair of electrons.

pH: pH may be defined as negative logarithm of hydronium ion concentration.

Solubility Product: Solubility product of an electrolyte at a specified temperature may be defined as the product of the molar concentrations of its ions in a saturated solution, each concentration raised to the power equal to the number of ions produced on dissociation of one molecule of the electrolyte.

Buffer Solution: A buffer solution is defined as a solution which resist any change in its pH value even when small amounts of the acid or the base are added to it.