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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 …