Skip to main content Accessibility help
×
  1. Home
  2. Browse subjects
  3. Engineering
  4. Chemical engineering
  5. Content listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

2477 results in Chemical engineering

Page 27 of 124

  • 15 - Thermodynamics

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    08 May 2019
    Print publication:
    16 May 2019, pp 793-889

  • Summary

    Introduction

    In our day-to-day life, we come across several instances in which one form of energy is converted into another form. When you rub your hands they become hot; similarly, if a piece of metal is hammered, it becomes hot. In both the above examples, mechanical energy is converted into heat energy. On the other hand, you are well aware that when water is heated, steam is generated, which is used to move turbines for the generation of electricity. Here, heat energy produces mechanical work. There can be numerous examples for the conversion of one form of energy into another. The science that deals with the interconversion of heat to work or any other form of energy is termed as thermodynamics. The term is self-indicative of what is happening – “thermo” is from temperature, which means energy and ‘dynamics’ pertains to motion or work. Chemical thermodynamics is a portion of thermodynamics that deals with the study of the processes in which chemical energy is involved.

    The principles of interconversion of energy in various forms are summarized in the three basic laws of thermodynamics. The first law is a statement of the law of conservation of energy, that is, energy cannot be created or destroyed, it can merely be converted from one form to another. The second law of thermodynamics explains the occurrence of various reactions spontaneously. It introduces the concept of ‘entropy’ or ‘disorder’ or ‘randomness’ to predict the spontaneous occurrence of chemical reactions. The third law of thermodynamics relates, among other things, to the experimental approach to absolute zero.

    Thermodynamics is a powerful tool for chemists. It studies the relationship between the effects of temperature on physical systems at the macroscopic scale. It helps in predicting whether a reaction will occur or not. It also helps to predict the direction in which a chemical reaction will occur.

    However, thermodynamics does not show how fast a reaction will proceed. Let us now deal with the fundamental concept of thermodynamics.

    Terminology of Thermodynamics

    It is necessary to define certain terms and expressions commonly used in thermodynamics.

    (I) System and surroundings

    System A thermodynamic system may be defined as that portion of the universe which is under observation or study.

  • 16 - Electrochemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    08 May 2019
    Print publication:
    16 May 2019, pp 890-967

  • Summary

    Introduction

    Electrochemistry is the branch of science which deals with the relationship between electrical energy and chemical energy and the inter-conversion of one form into other. If electrical energy brings about chemical reactions to occur, then the process is called electrolysis; for example, water can be made to split into hydrogen and oxygen by the passage of electric current. On the other hand, electrical energy can be produced as a result of chemical change. Both the above changes are called electrochemical changes and the latter finds use in the manufacture of cells and batteries, which generate electricity due to chemical changes. Both types of changes have widespread applications in chemistry. This chapter, however, deals only with the conversion of chemical energy into electrical energy and its applications in chemistry.

    Types of Conductors

    Conductors are substances which allow electricity to pass through them, for example, copper, silver and gold. Those substances which do not allow the passage of electric current through them are called non–conductors or insulators; for example, wood, rubber, etc.

    Conductors can be of two types:

  • (i) Metallic conductors Metallic conductors allow electricity to pass through them without undergoing any chemical change. The flow of electric current through metallic conductors is due to the flow of electrons in the metal. Common examples of metallic conductors are metals like copper, silver, etc.

  • (ii) Electrolytic conductors These are substances which allow electricity to pass through them in their molten states or in their aqueous solutions. Electric current brings about decomposition in them. The charge is carried by the ions and conduction occurs due to the movement of ions. Thus, these substances do not conduct electricity in solid state but in molten state or in aqueous solutions, as the ions can move about freely in molten state or in aqueous state. Substances like these are termed as electrolytes. Example: Molten solution of NaCl. The differences between metallic and electrolytic conductors are summarised in Table 16.1.

  • (iii) Non-electrolytes These are substances which do not conduct electricity at all, neither in their molten state nor in their aqueous solution. Example: sugar, glucose, urea, etc.

  • 4 - Phase Rule

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    08 May 2019
    Print publication:
    16 May 2019, pp 255-306

  • Summary

    Introduction

    The phase rule was given by Gibbs, which explains the equilibrium existing in heterogeneous systems. It states that the equilibrium between different phases is influenced by temperature, pressure and concentration only and not gravity, electrical or magnetic forces. The number of degrees of freedom (F), which will be explained later, is related to the number of components (C) and phases (P) by the following phase rule equation.

    Explanation of Terms

    Phase A phase is a homogenous, physically distinct and mechanically separable portion of a system which is separated from other parts of the system by a definite boundary.

    Examples

  • A gaseous mixture, being thoroughly miscible in all proportions constitutes one phase only.

  • If two liquids are immiscible (e.g., oil and water), they will constitute two separate phases.

  • Two miscible liquids (e.g., water and alcohol) constitute one phase only.

  • A solute completely dissolved in a solvent constitutes a single phase, for example, a solution of glucose in water, salt in water, etc.

  • At freezing point, water consists of three phases.

  • Each solid constitutes a separate phase. A mixture of rhombic and monoclinic sulphur is a two phase system.

  • A solid solution irrespective of the number of solids present is a single phase system.

  • Calcium carbonate decomposes as follows:

  • The above equilibrium has three phases (two solid and one gaseous)

  • Similarly,

  • Here there are two solid phases, Fe and FeO and one gaseous phase consisting of H2O(g) and H2(g). Hence, there are three phases in equilibrium.

  • A homogenous solution of Mohr's salt [FeSO4.(NH4)2SO4.6H2O] constitutes a single phase.

  • Components The number of components of a system at equilibrium is the smallest number of independently variable constituents by means of which the composition of each phase present can be expressed either directly or in the form of a chemical equation. While expressing the composition of a phase in terms of its components, zero and negative quantities are permissible. The components of a system do not represent the number of constituents or chemical individuals present in the system.

    • For example

  • (i) The sulphur system consists of four phases – rhombic, monoclinic, liquid and vapour.

  • 5 - Engineering Materials

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    08 May 2019
    Print publication:
    16 May 2019, pp 307-351

  • Summary

    Cement

    Introduction

    Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. It is used in construction for binding materials like bricks, stones and tiles, and is also used for flooring and plastering purposes.

    Cements used in construction can be either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) set and harden because of hydration and hydrolysis reactions between the anhydrous cement powder and water.

    Non-hydraulic cement such as slaked limes (calcium hydroxide mixed with water) harden due to the carbonation reaction by carbon dioxide present naturally in the air.

    Cement alone cannot be used for construction work. It is used as a mixture with sand and crushed stones. It may be used as mortar or concrete. Mortar It is a mixture of cement, sand and water which is used for binding bricks together and for plastering.

    Concrete It is a mixture of cement, gravel (crushed stones), sand and water. It is used in flooring works, columns, beams, foundations, etc. If instead of cement, lime is used, then the concrete is known as lime concrete.

    Reinforced concrete construction (RCC) It is concrete reinforced with steel rods or heavy wire mesh. Reinforced concrete is used in floors, beams, girders, columns, slabs, bridges, etc. It imparts high tensile strength to structures.

    Portland cement was discovered by Joseph Aspdin in 1824. The name Portland cement comes from the fact that the colour and quality of the resulting concrete are similar to Portland stone, a kind of limestone found in England.

    Types of cements

    The different types of cements based on Indian Standards are as follows:

  • Ordinary Portland cement It is the most important type of cement and is commonly called OPC. It is made by grinding and mixing clay and lime bearing minerals in proper proportions and then heating the mixture to nearly 1400 °C. It is not in much use these days, having been replaced by Portland pozzolana cement (PPC).

  • Portland pozzolana cement It can be fly ash-based or calcined clay-based. PPC is obtained by mixing OPC with suitable pozzolans at a certain temperature. Pozzolans are deposits of volcanic ash produced by rapid cooling. When mixed with slaked lime, pozzolans show properties similar to cement when it comes in contact with water. PPC is commonly used for various construction activities.

Page 27 of 124