Physical Chemistry

Intermolecular Forces in Liquids

Intermolecular Forces in Liquids – Intermolecular forces in liquids are collectively called van der Waals forces. – These forces are essentially electrical in nature and result from the attraction of charges of opposite sign.  – The principal kinds of intermolecular attractions are: (1) Dipole-dipole attractions (2) London forces (3) Hydrogen bonding.  …

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Gases – General Characteristics of gases

States of the matter – All matter exists in three states: gases, liquids and solids. – A molecular-level representation of gaseous, liquid and solid states is shown in the following Figure.   – A gas consists of molecules separated wide apart in empty space. The molecules are free to move …

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MCQ on Chapter Thermochemistry ΔH, ΔE

1. For exothermic reactions, ΔH is _______ while for endothermic reactions it is _______. (a) positive, negative (b) positive, positive (c) negative, negative (d) negative, positive Answer. (d) 2. The branch of chemistry which deals with the heat changes caused by chemical reactions is called _______ (a) thermodynamics (b) thermal …

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Measurement of The Heat of Reaction

Measurement of The Heat of Reaction – The experimental measurement of the heat of reaction or enthalpy change is known as calorimetry. – The name (calorimetry) evidently finds its origin in the unit of heat–the calorie. – The heat given out or absorbed in a chemical reaction is measured in …

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Energy Changes During Transitions or Phase Changes

Energy Changes During Transitions or Phase Changes

 – In this subject, we will discuss Energy Changes During Transitions or Phase Changes. Energy Changes During Transitions or Phase Changes – The three states of matter – solid, liquid and gas differ from one another in the arrangement of their constituent particles. – The magnitudes of intermolecular forces acting …

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Enthalpy of Reaction

Enthalpy of Reaction

– For reactions involving solids and liquids only the change in volume (ΔV) is very small and the term P × ΔV is negligible. For such reactions, the Change of Enthalpy of Reaction ΔH is equal to ΔE. Enthalpy of Reaction – Thermochemical measurements are made either at (a) constant …

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MCQ on the First law of Thermodynamics

MCQ on the First Law of Thermodynamics – In this subject, you will find 50 questions and answers MCQ on the First law of Thermodynamics 1. The first law of thermodynamics is_______ (a) the total energy of an isolated system remains constant though it may change from one form to …

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Adiabatic Expansion of an Ideal Gas

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 the adiabatic process there is no heat exchange between a system and surroundings, and q = 0. …

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Heat Capacity – Molar Heat Capacity

Molar Heat Capacity – 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 …

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Enthalpy of A System

Enthalpy of A System

– Enthalpy (H) is the total heat content of a system at constant pressure and is equivalent to the internal energy E plus the PV energy. Enthalpy of A System – In a process carried at constant volume (say in a sealed tube), the heat content of a system is …

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Joule-Thomson Effect

Joule-Thomson Effect

– The phenomenon of producing a lowering of temperature when a gas is made to expand adiabatically from a region of high pressure into a region of low pressure is known as the Joule-Thomson Effect or Joule-Kelvin Effect Joule-Thomson Effect – Joule and Thomson (later Lord Kelvin) showed that when …

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