Definitions of Chemistry

1. ION:- 

           An atom or group of atoms that can exist independently with a charge is called an “ION”. 

                                           (Or) 

             Loss or Gain of electrons

2. ATOM:-

           These are the smallest particle of a matter which may or may not exist independently.

3. MOLECULE:-

            These are the smallest particles of a matter which exists independently.

4. SYMBOL:-

             It is the shortest form of an element which represents the number of atoms in that.

5. EQUATION:-

             An equation represents a chemical reaction in which there are the reactants and products in symbolic form.

6. RADICAL:-

            An atom or group of atoms can exist independently with charges and are formed by loss or gain of electrons.

7. EMPIRICAL FORMULA:-

             It is the formula of a molecule that contains the least possible ratio of atoms.

8. MOLECULAR FORMULA:-

             It represents the ratio of the atoms in a molecule or a compound which are actually present in that.

9. COMPOUND:-

          Two elements combine chemically is called a compound.

10. ELEMENT:-

          It is a pure substance.

                    (Or)

           Molecules made of identical atoms.

11. MATTER:-

          Which has weight and occupies space     

12. CHEMISTRY:-

          It is the science which deals with all kinds of matter and their changes.

13. VALENCY:-

          The combining capacity of any element is called valency.

14. MOLECULAR WEIGHT:-

           The molecular weight of a molecule is the sum of weights of atoms present in it.

15. DISTILLATION:-

          Condensation followed by evaporation is called distillation.

16. SOLUTION:-

          Solid is mixed with liquid to form solution.

17. BURNING:-

           Burning means treating with oxygen 

18. CIRCUIT:-

           Containing coil is called circuit.

19. NEUTRALIZATION:-

           Forming of salts and water from basics and acids

20. SUBLIMINATION:-

           On heating some solids substances changes directly into vapor without becoming liquids. This process is known as sublimination.

21. PHYSICAL CHANGE:-

           A physical change is a change which can be brought back to the normal condition easily.

22. CHEMICAL CHANGE:-

           A chemical change is a change in which substances will change and can not be brought back to their normal condition easily.

23. CHEMICAL COMBINATION:-

           In a chemical combination two elements are compound always combines in definite ratio to form a larger compound.

24. CHEMICAL DECOMPOSITION:-

           In a chemical decomposition always a larger compound divides under special conditions into smaller compound or elements.

25. CHEMICAL DISPLACEMENT:-

            In a chemical displacement reaction the elements of higher reactivity will displace the elements of lower reactivity.

26. CHEMICAL DOUBLE DECOMPOSITION:-

            In the chemical change there will be the exchange of radicals between two compounds.

27. MIXTURE:-

            It is an impure substance which is made up of different kinds of molecules.

                                            (Or)

               If the elements or compounds are combine physically. There they form a mixture.

28. FORMULA:-

            It is the short form of a molecule.

                                           (Or)

              It represents the actual number of constituents of atoms present in the molecules.

29. RUST:-

           Iron reacts with the moist air and forms rust.

    Formula of Rust:-Fe2o3.

30. REACTANTS:-

           The substances which take part in the reaction, they should be written on the left side.                  

31. PRODUCTS:-

            The substance formed in the reaction is called products. They should be written on the right side of the arrow mark.

32. ACIDS:-

             Substances with sour taste and changing blue litmus to red

33. BASES:-

            Substance with sticky nature and changing red litmus to blue are called Alkalies or Bases.

34. LAW OF CONSERVATION OF MASS:-

                During a chemical change matter is neither created nor destroyed but it undergoes physical and chemical change.

35. LAW OF DEFINITE PROPOSITION:-

             When two or more elements combine to form a compound, they combine in a fixed ratio of their weights. The ratio is independent of the method of formation of the compound.

36. LAW OF MULTIPLE PROPOSITION:-

              The weight of one element that separately combine with a fixed weight of another element to form two or more compound tears a simple integral ratio.

37. SOFT WATER:-

          Water which produces lather sufficiently with a soap is called soft water.

38. HARD WATER:-

           Water which does not produce lather property with soap is called hard water.

39. CHLORINATION:-

           In this process a small quantity of chlorine is added to water in order to kill the microbes which cause illness.

40. OXY-HYDROGEN FLAME:-

              Hydrogen generates enormous heat (2400°c) when it burns in the presence of oxygen. It is used for cutting and welding metals.

41. HYDROGENATION OF OILS:-

            Conversion of vegetable oils into solid fats by passing hydrogen through them under pressure is called hydrogenation of oils.

42. CATALYST:-

            Catalyst is a substance which alters the rate of a chemical reaction, without itself undergoing any permanent chemical change.

43. OXIDATION:-

             The chemical reaction of any substance with oxygen or removal of hydrogen from a substance is called oxidation.

                                           (Or)

               Loss of electrons is called oxidation.

44. REDUCTION:-

           Removal of oxygen from a compound is called reduction.

                                             (Or)

             Gain of electrons is called reduction.

45. COMBUSTION:-

           Burning substances in oxygen or air is called combustion.

46. AIR POLLUTION:-

         The contamination of air by dust and toxic vapors is called air pollution.

47. ALLOTROPY:-

           The existence of an element in two or more different physical forms is called allotropy.

48. PHOSPHORESCENCE:-

           If phosphorus is exposed to air in dark, it glows because of slow combustion. This is called phosphorescence.

49. NITROGEN FIXATION:-

           Conversion of atmospheric nitrogen nitrate salts is called nitrogen fixation.

50. COMPRESSIBILITY:-

             Decrease in the volume of the same quantity of gas under pressure is known as compressibility.

51. CHEMICAL EQUATION:-

             Chemical equation is a short hand representation of a chemical change or reduction in terms of symbols and formulae.

52. OXYGEN:-

 PREPARATION OF OXYGEN:-

             

                          

                          

                          

                         

                         

 PHYSICAL PROPERTIES:-

              Oxygen is a colorless, tasteless and odourless gas. It is slightly heavier than air and slightly soluble in water. It is neutral to litmus. It has no effect on wet litmus paper. 

 CHEMICAL PROPERTIES:-

              

                            

                           

                           

                          

 OXIDATION:-

              

                            

                           

                           

 REDUCTION:-

             

                           

 TEST FOR OXYGEN:-

          When we introduce a burning splinter into the oxygen gas in burns brightly

53. SEDIMENTATION:-

          Water in the form of crystals is called sedimentation.

54. OXIDIZING AGENT:-

           The substance which oxidizes is known as oxidizing agent.

55. REDUCING AGENT:-

            Hydrogen which removes oxygen from the compounds is called reducing agent.

56. HYDRIDES:-

             Hydrogen reacts with many elements to form compounds is called hydrides.

57. TRICKS OF CHEMISTRY:-

             

               

               

               

58. CHARLE’S LAW:-

            At constant pressure the volume of given mass of gas increases with an increase in temperatures and decreases with decrease in temperature by a value of 1/273 of the original volume at 0°c for every one degree centigrade change in temperature.

59. CHEMICAL BOND:-

            The atom in a molecule is held together by forces of attraction and this force is called a chemical bond.

60. ELECTRONIC CONFIGURATION:-

            It is defined as a systematic arrangement of electrons in the atomic orbits.

61. COVALENT BOND:-

           A bond formed by the sharing of a pair of electrons between two atoms each atom contributing one electron to the shared pair is called covalent bond.

62. COVALENT MOLECULE:-

          Molecules whose atoms are joined by covalent bonds are called covalent molecules.

63. BOND DISSOCIATION ENERGY:-

           Energy which is required to break the bond is called bond dissociation energy.

64. BOND ENERGY:-

             The certain amount of energy which is released when a new bond is formed is called bond energy.

65. ENDOTHERMIC REACTION:-

            It is a chemical reaction which takes place with the absorption of heat.   

66. EXOTHERMIC REACTION:-

             It is a chemical reaction which is accompanied by the release of heat energy.  

                                               (Or)

                Reaction in which heat is evolved is known as exothermic reactions.                 

67. ELECTROCHEMICAL REACTIONS:-

              The reactions which take place only with the absorption of electrical energy are called electrochemical reactions.

68. GRAM MOLECULAR WEIGHT:-

           It can be defined as the relative molecular mass of a substance expressed in grams with reference to the atomic weight of hydrogen.

69. THERMOCHEMICAL REACTIONS:-

            Equations representing heat energy in chemical reactions are called thermo chemical reactions.

70. FAST REACTIONS:-

             Reactions which take place within a second are known as fast reactions.

71. MODERATE REACTION:-

              Reactions taking place in a few minutes to a few hours is termed as moderate reactions.

72. SLOW REACTIONS:-

              Reactions taking place in several hours and above are known as slow reactions.

73. MINERALS:-

           Compounds of metals which occur in nature with other materials such as sand, rock and clay as impurities and which are obtained by mixing are called minerals.

74. ORES:-

          The minerals from which metals can be profitably extracted are called ores.

75. METALLURGY:-

          The method of extraction of the metals from their ores and the preparation of alloys is called metallurgy.

76. ORE DRESSING OR CONCENTRATIONS:-

           The removal of unwanted impurities by mechanical and other physical methods is known as ore dressing or concentration.

77. CALCINATION:-

           It is a process in which ore is subjected to the action of heat in the absence of air.

78. ROASTING:-

            It is a process in which ore is heated in the presence of air.

79. MONOATOMIC:-

            The atom which has single atom is called mono atomic.

80. DIATOMIC MOLECULES:-

            The molecule which has two atoms is called diatomic molecules.

81. CONSTITUENTS:-

             The substances present in the mixture are called constituents.

82. DECANTATION:-

             Separating a clean liquid from the solid sediment is called decantation.

83. FILTRATION:-

            It is a process of separating very fine undissolved solid particles present in a liquid quickly or completely.

84. EVAPOURATION:-

            It is a process in which we get back the dissolved solid from a solution by heating.

Mechanical Definitions

 

•      Brayton cycle- A thermodynamic cycle that describes gas turbine engines. Inlet gas is brought to high pressure through a compressor, after which it is heated in a combustion chamber and expanded through a turbine for energy extraction. It is an "open" system, in that the working fluid is not recycled.

•      Rankine cycle- Also referred to as the steam cycle, the Rankine cycle utilizes the evaporation-condensation properties of a working fluid to drive a turbine. Water vapor, or steam, is often used as the working fluid for these processes. A pump is used to circulate the fluid through a boiler, where it is heated (or boiled) at a constant pressure into steam, after which it is expanded through a turbine for energy extraction.  It is a "closed" system, in that the working fluid is recycled.

•      Combined cycle (CC)- A combined cycle system utilizes two or more thermodynamic cycles to recover energy from hot exhaust gas streams. These cycles often combine Brayton and Rankine cycles in series, through the use of a "heat recovery steam generator" or HRSG. This device is a large heat exchanger used to extract heat from exhaust gases to boil water in a Rankine cycle.

•      Combined heat and power (CHP)- Similar to a combined cycle process, CHP cycles are used to generate steam for functions beyond generating electricity. These functions can include space heating, process heating, or direct steam use.

•      Turbine- A rotor-machine that is used to extract energy from high pressure, high temperature fluids via expansion across the turbine blades.

•      Heat Recovery Steam Generator (HRSG)- A specialized heat exchanger often used in power generation. These devices will produce steam for a specific process or to drive a steam turbine.

•      Heat rate - A ratio of incoming fuel energy (in BTU) to outgoing electrical energy (in kWh). Heat rates are a convenient way to assess the efficiency of a power plant. These rates will be larger than one (normally around the magnitude of 10,000) and indicate increases in effiency as the number goes down.

•      Hybrid electric vehicle (HEV)- Features a parallel drivetrain architechture, with a battery-driven electric motor and an internal combustion engine coupled into the same transmission. Usually features energy recovery technology to recharge the battery during operation

•      Plug-in hybrid electric vehicle (PHEV)- Similar to HEVs, PHEVs utilize a two-way transmission to couple a gas burning engine with a battery-driven motor. Battery packs can be recharged using external power from a wall outlet.

•      Battery electric vehicles (BEV)- Electric vehicles driven purely by an electric motor. The BEV battery pack must be charged using external power from a wall outlet.

•      Torque-speed plots- A graphical plot used to characterize the performance of engines and motors. These plots are related to the power output of the engine or motor.

•      Natural gas vehicles (NGV)-Vehicles driven by natural gas instead of liquid gasoline. Traditional internal combustion engines can be adapted to burn natural gas, with a large part of the converstion stemming from different fuel storage requirements.

The mass (m) of a body is the measure of the amount of material present in that body.

 

The weight (wt) of a body is the force exerted by that body when its mass is accelerated in a gravitational field.

 

The specific volume ( ν ) of a substance is the total volume (V) of that substance divided by the total mass (m) of that substance (volume per unit mass).

 

The density ( ) of a substance is the total mass (m) of that substance divided by the total ρ volume (V) occupied by that substance (mass per unit volume).

 

Specific gravity (S.G.) is a measure of the relative density of a substance as compared to the density of water at a standard temperature

 

Humidity is the amount of moisture (water vapor) in the air.

 

Absolute humidity is the mass of water vapor divided by a unit volume of air (grams of water/cm3 of air)

 

Relative humidity is the amount of water vapor present in the air divided by the maximum amount that the air could contain at that temperature. Relative humidity is expressed as a percentage.

 

An intensive property is independent of the amount of mass.

 

Extensive properties are those that vary directly with the mass.

 

Temperature is a measure of the molecular activity of a substance. The greater the movement of molecules, the higher the temperature.

 

The absolute temperature scale that corresponds to the Celsius scale is called the Kelvin (K) scale.

 

The absolute scale that corresponds to the Fahrenheit scale is called the Rankine (R) scale.

 

Pressure is a measure of the force exerted per unit area on the boundaries of a substance (or system). It is caused by the collisions of the molecules of the substance with the boundaries of the system.

 

When pressure is measured relative to a perfect vacuum, it is called absolute pressure (psia).

 

When pressure is measured relative to atmospheric pressure (14.7 psi), it is called gauge pressure (psig).

 

Energy is defined as the capacity of a system to perform work or produce heat.

 

Potential energy (PE) is defined as the energy of position.

Kinetic energy (KE) is the energy of motion.

 

The specific internal energy (u) of a substance is its internal energy per unit mass.

 

Specific enthalpy (h) is defined as h=u+Pν, where u is the specific internal energy (Btu/lbm) of the system being studied, P is the pressure of the system (lbf/ft2 ), and ν is the specific volume (ft3 /lbm) of the system.

 

Work is defined for mechanical systems as the action of a force on an object through a distance.

 

A positive value for work indicates that work is done by the system on its surroundings; a negative value indicates that work is done on the system by its surroundings.

 

A positive value for heat indicates that heat is added to the system by its

surroundings

 

The heat added to or removed from a substance to produce a change in its temperature is called sensible heat.

 

Latent heat is the amount of heat added to or removed from a substance to produce a change in phase.

 

Latent heat of fusion is the amount of heat added or removed to change phase between solid and liquid.

 

Latent heat of vaporization is the amount of heat added or removed to change phase between liquid and vapor.

 

The ratio of the heat (Q) added to or removed from a substance to the change in temperature (∆T) produced is called the heat capacity (Cp) of the substance.

 

The heat capacity of a substance per unit mass is called the specific heat(cp) of the substance.

 

Power is defined as the time rate of doing work. It is equivalent to the rate of the energy transfer.

 

Entropy is sometimes referred to as a measure of the inability to do work for a given heat transferred.

 

A system in thermodynamics is nothing more than the collection of matter that is being studied.

 

An isolated system is one that is not influenced in any way by the surroundings. This means that no energy in the form of heat or work may cross the boundary of the system. In addition, no mass may cross the boundary of the system.

 

A closed system has no transfer of mass with its surroundings, but may have a transfer of energy (either heat or work) with its surroundings.

 

An open system is one that may have a transfer of both mass and energy with its surroundings.

 

A control volume is a fixed region in space chosen for the thermodynamic study of mass and energy balances for flowing systems. The boundary of the control volume may be a real or imaginary envelope.

 

The control surface is the boundary of the control volume.

 

 

Steady state is that circumstance in which there is no accumulation of mass or energy within thecontrol volume, and the properties at any point within the system are independent of time.

 

The path of the succession of states through which the system passes is called the thermodynamic process.

 

When a system in a given initial state goes through a number of different changes in state (going through various processes) and finally returns to its initial values, the system has undergone a cyclic process or cycle.

A reversible process for a system is defined as a process that, once having taken place, can be reversed, and in so doing leaves no change in either the system or surroundings.

 

An irreversible process is a process that cannot return both the system and the surroundings to their original conditions.

 

An adiabatic process is one in which there is no heat transfer into or out of the system. The system can be considered to be perfectly insulated.

 

Isentropic Process

An isentropic process is one in which the entropy of the fluid remains constant. This will be true if the process the system goes through is reversible and adiabatic. An isentropic process can also be called a constant entropy process.

 

Polytropic Process

When a gas undergoes a reversible process in which there is heat transfer, the process frequently takes place in such a manner that a plot of the Log P (pressure) vs. Log V (volume) is a straight line. Or stated in equation form PVn

= a constant. This type of process is called a polytropic process.

 

A throttling process is defined as a process in which there is no change in enthalpy from state one to state two, h1 =h2 ; no work is done, W = 0; and the process is adiabatic, Q = 0

First Law of Thermodynamics :

Energy can neither be created nor destroyed, only altered in form.

 

Second Law of Thermodynamics :

It is impossible to construct a device that operates in a cycle and produces no effect other than the removal of heat from a body at one temperature and the absorption of an equal quantity of heat by a body at a higher temperature.

Critical Point:- The temperature and pressure above which there is no distinction between the liquid and vapor phases.

 

Triple point - the temperature and pressure at which all three phases can exist in equilibrium .

 

Sublimation - change of phase from solid to vapor

Vaporization - change of phase from liquid to vapor

Condensation - change of phase from vapor to liquid

Fusion or melting - change of phase from solid to liquid

 

Boyle's Law

The pressure of a gas expanding at constant temperature varies inversely to the volume.

 

Charles' Law

The pressure of a gas varies directly with temperature when the volume is held constant, and the volume varies directly with temperature when the pressure is held constant.

 

1 ft-lbf = 1.286 x 10-3 Btu = 3.766 x 10-7kW-hr

1 Btu = 778.3 ft-lbf = 2.928 x 10-4kW-hr

1 kW-hr = 3.413 x 103Btu = 2.655 x 106 ft-lbf

 

 

 

 

 

 

The term saturation defines a condition in which a mixture of vapor and liquid can exist together at a given temperature and pressure.

 

The temperature at which vaporization (boiling) starts to occur for a given pressure is called the

saturation temperature or boiling point.

The pressure at which vaporization (boiling) starts to occur for a given temperature is called the

saturation pressure.

 

The graphical representation of this relationship between temperature and pressure at saturated

conditions is called the vapor pressure curve.

 

When a substance exists as part liquid and part vapor at saturation conditions, its quality (x) is

defined as the ratio of the mass of the vapor to the total mass of both vapor and liquid.

 

If the temperature of the liquid is lower than the saturation temperature for the existing pressure,

it is called either a subcooled liquid (implying that the temperature is lower than the saturation

temperature for the given pressure) or a compressed liquid (implying that the pressure is greater

than the saturation pressure for the given temperature).

 

The moisture content of a substance is the opposite of its quality. Moisture (M) is defined as

the ratio of the mass of the liquid to the total mass of both liquid and vapor.

 

If a substance exists entirely as vapor at saturation temperature, it is called saturated vapor.

 

When the vapor is at a temperature greater than the saturation temperature, it is said to exist as

superheated vapor.

 

 

 

Property Diagrams: The phases of a substance and the relationships between its properties are most commonly shown on property diagrams. There are six different types of commonly encountered property diagrams. These are: Pressure- Temperature (P-T) diagrams, Pressure-Specific Volume (P-ν) diagrams, Pressure-Enthalpy (P-h) diagrams, Enthalpy-Temperature (h-T) diagrams, Temperature-entropy (T-s) diagrams, and Enthalpy-Entropy (h-s) or Mollier diagrams.

 

The line that separates the solid and vapor phases is called the sublimation line.

The line that separates the solid and liquid phases is called the fusion line.

The line that separates the liquid and vapor phases is called the vaporization line.

The point where the three lines meet is called the triple point. The triple point is the only point at which all three phases can exist in equilibrium.

The point where the vaporization line ends is called the critical point.

The Mollier diagram can be used to determine various properties of a fluid.

Mollier diagram is an h versus s plot.

Can only be used when quality is greater than 50% and for superheated steam.

Contains a series of constant temperature, constant pressure, constant moisture content, and constant superheat lines.

Harvesting Ocean Energy

 

Climate Change Impact

 

Air and Sunlight into Carbon Neutral Jet Fuel

 

Advanced Welding Material Selection & Compatibility Matrix

Advanced Welding Material Selection & Compatibility Matrix

A comprehensive guide for matching base metals, filler materials, and welding conditions.

This matrix is tailored for Welding Engineers, Inspectors, and Trainers to ensure proper material compatibility and process selection.

Pro Tips: 

A. Always match filler metal chemistry with joint performance needs (strength, ductility, corrosion).

B. Refer to WPS, PQR & MTCs before executing any joint.

C. Strictly monitor interpass temperature and cooling rate – especially for crack-sensitive materials.

D. Cleanliness, fit-up, and joint preparation are critical to avoid defects.