Physical Chemistry

Heat of Combustion ❒ The heat of combustion of a substance is defined as: The change in enthalpy of a system when one mole of the substance is completely burnt in excess of air or oxygen. ❒ It is denoted by ΔHc. As for example, heat of combustion of methane is – 21.0 kcal …

Heat of Formation ❒ The heat of formation of a compound is defined as:The change in enthalpy that takes place when one mole of the compound is formed from its elements. ❒ It is denoted by ΔHf . For example, the heat of formation of ferrous sulphide and acetylene may be expressed as: ❒ Similarly, the …

The heat or enthalpy changes accompanying chemical reactions are expressed in different ways, depending on the nature of the reaction. These are discussed below. (1) Heat of Formation ❒ The heat of formation of a compound is defined as:The change in enthalpy that takes place when one mole of the …

Heat of Reaction or Enthalpy of Reaction ❒The heat of a reaction is simply the amount of heat absorbed or evolved in the reaction. ❒ We also know that the amount of heat absorbed or evolved at constant temperature and pressure is called enthalpy. Therefore the amount of heat change …

Enthalpy of a Reaction ❒Thermochemical measurements are made either at (a) constant volume or (b) constant pressure. The magnitudes of changes observed under the two conditions are different. ❒ The change in internal energy (ΔE): is the heat change accompanying a chemical reaction at constant volume because no external work …

1. The study of the flow of heat or any other form of energy into or out of a system undergoing physical or chemical change is called_______ (a) thermochemistry  (b) thermokinetics (c) thermodynamics (d) thermochemical studies Answer. (c) 2. Thermodynamics is applicable to_______ (a) microscopic systems only  (b) macroscopic systems …

Adiabatic Expansion of an Ideal Gas ❒ A process carried in a vessel whose walls are perfectly insulated so that no heat can pass through them, is said to be adiabatic.❒ In adiabatic process there is no heat exchange between a system and surroundings, and q = 0. ❒ According …

Molar Heat Capacities ❒ By heat capacity of a system we mean the capacity to absorb heat and store energy. As the system absorbs heat, it goes into the kinetic motion of the atoms and molecules contained in the system. This increased kinetic energy raises the temperature of the system. …

Enthalpy of A System ❒ In a process carried at constant volume (say in a sealed tube), the heat content of a system is the same as internal energy (E), as no PV work is done.  ❒ But in a constant-pressure process, the system (a gas) also expends energy in …

Joule-Thomson Effect ❒ Joule and Thomson (later Lord Kelvin) showed that when a compressed gas is forced through a porous plug into a region of low pressure, there is appreciable cooling. ❒ The phenomenon of producing lowering of temperature when a gas is made to expand adiabatically from a region …

Internal Energy ❒ A thermodynamic system containing some quantity of matter has within itself a definite quantity of energy. This energy includes not only the translation kinetic energy of the molecules but also other molecular energies such as rotational, vibrational energies. The kinetic and potential energy of the nuclei and …

  Nature of Heat and Work  When a change in the state of a system occurs, energy is transferred to or from the surroundings. This energy may be transferred as heat or mechanical work.  We shall refer the term ‘work’ for mechanical work which is defined as: force × distance. …

  Thermodynamic Processes ❒  When a thermodynamic system changes from one state to another, the operation is called a Process. ❒ These processes involve the change of conditions (temperature, pressure and volume). ❒ The various types of thermodynamic processes are: (1) Isothermal Processes (2) Adiabatic Processes (3) Isobaric Processes (4) …

  What is Thermodynamic ? ❒ Thermodynamics:  is The study of the flow of heat or any other form of energy into or out of a system as it undergoes a physical or chemical transformation. ❒ In studying and evaluating the flow of energy into or out of a system, …

  ❒ In the previous subject we talk about the concept of Hybridization and the types of Hybridization, but in this subject we will talk about Hybridization and Shapes of Molecules. ❒ Diatomic molecules must all be invariably linear but tri-and tetra-atomic molecules have several possible geometrical structures. In this …

     While formation of simple molecules could be explained adequately by overlap of atomic orbitals, the formation of molecules of Be, B and C present problems of greater magnitude having no solution with the previous theory. To explain fully the tendency of these atoms to form bonds and the …

  preface of This book      The book is divided into four parts. The first part focuses on the macroscopic properties of physical systems. It begins with the descriptive study of gases and liquids, and proceeds to the study of thermodynamics, which is a comprehensive macroscopic theory of the behavior …

  preface of This book      Two very important fields of natural science—chemistry and the science of electricity— matured and grew vigorously during the first half of the nineteenth century. Electrochemistry developed simultaneously. From the very beginning, electrochemistry was not merely a peripheral field but evolved with an important …

Bond Formation (Valence Bond Theory) – Bond formation between atoms to give chemical compounds can be interpreted admirably in terms of the orbital theory of atomic structure. – Heitler and London believed that electron cloud of the valence orbital on one atom ‘overlaps’ the electron cloud of the other bonding …

    1. The valency of an element is ___________ (a) the combining capacity of one atom of it (b) the number of bonds formed by its one atom (c) the number of hydrogen atoms that combine with one atom of it (d) all the above Answer. (d) 2. The …