Molar Heat of Vaporization of Water

Elements or compounds participate in reactions by means of their molecules and not atoms.This was postulated and proved by Avogadro.

The molecules are composed of atoms of same or different elements. In case of monatomic molecules of elements,there is no difference between the composition of molecule and atom.
The mass of the molecule is mass of constituent atoms which in turn is the mass of those atoms.
Therefore it can be said that the mass of a molecule is the sum of masses of protons and neutrons in the molecule.This is molar mass.The molar mass units is a.m.u.

What is the significance of the mass of the molecule and how is it related to mole or molar....?
A mole is molar mass expressed in terms of g.

It was proved by Avogadro that when the elements or compounds enter into a reaction,they do so not by their pure mass,but by the mass expressed in terms of grams.
e.g.

Formation of  ammonia
N₂ + 3H₂ ---------> 2NH₃
As mentioned above, it is not that 1g of nitrogen would combine with 3 g of hydrogen to form 2 g of ammonia.

However it is that 1mole of nitrogen would combine with 3 moles of hydrogen to form 2 moles of ammonia.
All the properties of compounds are related to moles or molar quantities.

Heat of Vaporization

Whenever a water is heated to a certain temperature, it undergoes two changes.

In the beginning the energy supplied is used to increase the energy of the molecules in the same liquid phase.The heat energy supplied from outside is utilised to increase the vibrating energy of the molecules which is noticed in form of rise in the temperature of the water.

In the second phase,the energy absorbed by the molecules, after reaching a threshold, no longer is used to increase the temperature but breaking the intermolecular attractions.

The intermolecular forces are overcome at a specific temperature which is called as boiling point.The liquid molecules which overcome these intermolecular forces turn into gas phase [steam].This process is called vaporization

The energy supplied beyond this boiling point is not utilized to increase the temperature but to overcome the intermolecular forces,by more and more number of molecules.As a result they vaporize accordingly.

When quantified, it was found that the energy required to vaporize a mole of water,called, molar heat of vaporization of water, is is 49.79 kJ/mole.
In other words,to vaporize one mole of water energy required is 49.79 kJ.

Atomic Mass of Iron

Iron is denoted by the symbol Fe. (Ferrum).    It belongs to Period 4 and Group 8 in the periodic table. It is grayish white in color with a specific gravity of 7.86.  Its atomic number is 26 and relative atomic mass is 55.85.  It exhibits variable valency  – 2 & 3.  

Introduction to atomic mass of iron

Atomic mass is the total number of neutrons and protons in the nucleus of the atom.  Atomic number is the total number of electrons or protons in an atom.  The electronic configuration is 2, 8, 14, 2.   The number of electrons in the atom is 26, which is equal to the number of protons. 

Atomic mass (A) = number of Protons (p) + number of Neutrons (n). 

Number of protons = number of electrons.

Atomic mass of iron = 26 + 29.85 = 55.85.

Atomic number of iron = 26

More about Atomic Mass of Iron

A close look at the electronic configuration of lighter elements reveals that those elements which had even number of protons, that is atomic number like 2He4, 6C12 etc. have their mass number twice their atomic number – except 4Be9 and 18Ar40.  Elements which have odd number of protons like 3Li7, 5B11 etc. have their mass number twice the atomic number + 1. (A = 2 Z +1) except 7 and 14 and 1H1.  This is not the case with heavier elements.  That is why iron, whose atomic mass is 26 does not have 52 as its mass number. 

Iron is not found in native state; it occurs only in combined state in its ore.  In this form, iron makes 5% of earth’s crust.  It is the second most abundant metal after aluminum.  

The ores of iron are red hematite (anhydrous ferric oxide) Fe2O3, brown hematite (hydrated ferric oxide) 2Fe2 O3. 3H2O, magnetite (triferric tetroxide) Fe3O4,  iron pyrites (iron disulphide) FeS2 and Siderite (ferrous carbonate) FeCO3. 

Iron is a heavy metal.  It is malleable and possesses high tensile strength.  It is a good conductor of heat and electricity.  It melts at 1535 degree Celsius.  It can be magnetized.

Specific Heat Capacity Table

Specific heat capacity table shows values of specific-heat capacity for some common substances. Some tables also show the specific heat capacity of different substances in different units.

High Specific Heat

Specific heat is defined as amount of energy required to raise the temperature of a unit mass by one degree Celsius. Each element has its particular specific heat. Specific-heat of water is defined as amount of energy required to raise the temperature of one gram water by one degree Celsius. It account for 1 Cal/ gram *C for water. Hence water has high value of specific heat. The high specific heat of water gives it some unique physical properties. Water also serves as temperature regulator in living organisms due to its high specific heat. As it need a high amount of energy (1 Cal/ gram) to raise the temperature of water which is normally not available under room temperature. Hence water serves to maintain the body temperature to a almost constant value.

Calculating Specific Heat

Specific heat is the amount of energy required to raise the temperature of one unit mass of a substance by one degree Celsius. It is expressed by following equation:

C=Q / (m* �� t)

Here C= specific heat

Q= amount of energy added

m=mass of substance

�� t= temperature of substance before adding heat- temperature of substance after adding heat energy.

Calorimetry Equation:

Calorimetry is a specific device where the chemical reaction and physical processes are carried out. The device serve as isolated system as the calorimetry walls made up of insulated materials, hence there is no energy exchange with surroundings.

The equations of calorimetry depends on its types, bomb calorimetry, classical calorimetry, etc.

The name bomb calorimetry is given to the constant volume calorimetry.

We will look for the equation of the bomb calorimetry;

Qreaction = -(Qwater + Qbomb)

where;

q is the heat flow

What is Specific Heat Capacity

Specifc heat capacity is the amount of energy required to raise the temperature of a unit mass of any substance or gas by one degree Celsius. Here energy should be used in raising temperature of the substance only, not in the phase change. Specifc heat capacity can be measured at constant volume and constant pressure.

pecific heat capacity of a substance at constant pressure is expressed as

Cp= (δh/δT)p; and

Specific heat capacity of a substance at constant volume is expressed as following formula:

Cv=(δU/δT)v.

What is Magnetism

Magnetism is the property of a material by which it gets attracted or repelled by a magnetic force in a magnetic field. It is produced due to two reasons:

First is by the inherent existing property of particles in a material such as magnets.

Secondly by the moving charged particles in which magnetism is induced.

All those objects which possess magnetism have a magnetic field associated with them. A magnetic field is the region around the object, in which the object attracts or repels other magnetic material in that region. Magnetic field contains imaginary lines of force known as magnetic field lines. Each magnetic object has a north (N) pole and a south-pole (S) end. The magnetic lines of force emerge out of the north pole of the object and goes into the object at south - pole. These lines of force are perpendicular at the surface of the object. Also the magnetic field lines are continuous lines.

Magnetic Fields are not only associated with the magnets but also with the conductors which carry electric current through them. The moving charged particles inside the conductor induce magnetism in it thereby developing magnetic field around them. The movement of the particles can be a spin, transnational motion etc like spin of a proton or translation of electrons in a current carrying conductor.

The Magnetic Fields of the magnetic objects creates a magnetic force on other bodies with magnetic field. This force is the property known as magnetism  The magnetic force of two objects is attractive if the objects are facing opposite poles (N-S or S-N) and it is repulsive if they face same magnetic poles (S-S or N-N).

Magnetic field applies a force on a charged particle which is passing through it. The force occurs in the direction perpendicular to the direction of movement of charge and that of the magnetic field. This applied force is known as Lorentz force. Lorentz force is also applied in a current carrying wire as the wire contains large number of charged particles (electrons, protons) in it.

The amount of magnetic field or magnetic field line that passes through a surface area is known as 

Magnetic Flux (φ) which varies with the surface area of the body, magnetic field (B) and its alignment with the surface area (A). Magnetic flux with a given strength of magnetic field and surface area will be maximum if the magnetic field lines are perpendicular to the surface.

φ=(B.A)cosӨ

Ө is angle between magnetic field and normal to the surface.

Latent Heat of Vaporization

Introduction :

Latent is a Latin word which means hidden. Latent heat is hidden heat, which a body absorbs or releases when it changes form one state to another.

Latent heat of vaporization of a substance is the amount of heat required to change one unit mass of that substance from liquid to gaseous state. During this process, the temperature of the substance remains constant. The heat absorbed in the process used to change the state of that substance from liquid to gaseous state. The heat energy increases the internal energy of the substance in form of change of state with no rise in temperature. A substance starts changing its state from liquid to gaseous state upon reaching its boiling point. When change of state starts taking place, the temperature of the liquid becomes constant at the boiling point. The heat absorbed there after used up in changing its state from liquid to gaseous state.

Latent Heat of Vaporization :

Similar to the latent heat of vaporization, there is latent heat of fusion. Just like the latent heat of vaporization, it is the heat required by a substance to change from solid to liquid state. In this case, also there is no rise in temperature when change of state takes place.

Latent Heat of Vaporization :

For a particular substance, Latent heat of vaporization per unit mass is more than its specific heat. For example, Latent heat of vaporization of water is 2260 J/g whereas its specific heat is just 4.2 J/g per degree centigrade rise in temperature. That is why burn caused by steam at 100 degree centigrade is more severe than burn caused by water at 100 degree centigrade.  Similarly, ice at zero degrees centigrade is cooler than water at zero degrees centigrade.

We can conclude one should be more cautions in burns caused be steam because latent heat of vaporization comes into play causing more severe burns.

J.J. Thomson's atomic model

Joseph John Thomson was Danish Physicist, who discovered the 'electrons' in 1897 and put forward his famous ‘plum pudding model’ of atom in 1904.The structure of atom was put forth by many scientists. John Dalton, J.J. Thomson, Rutherford and Bohr are the important scientists who worked in this field.

The following are the work of various scientists in framing the structure of atom:

• John Dalton discovered that matter is made of very small particles called atoms which can not be divided.
• J.J. Thomson discovered electrons and found that the atom can be divided and it is made of positive core and negatively charged particles embedded in it.
• James Chadwick discovered the protons.
• Goldstein discovered neutrons.
• Rutherford discovered that atom has a positive central core called nucleus and the electrons move around the nucleus in great speed.
• Bohr stated that the electrons move around the nucleus in a definite energy levels called shells and gave the explanation for the stability of atom.

Discovery of Atom

It was John Dalton, who stated that the matter is made of indivisible small particles called atoms. Atom means 'that which can not be divided'. This model was discarded by J.J. Thomson when he discovered the electrons.

J.j. Thosmson Atomic Model

 Michael Faraday worked on the passage of electricity through liquids while Thomson worked on the passage of electricity through gases. During this experiment, Thomson discovered the electrons.
According to Thomson, when a glass tube fitted with two electrodes filled with a gas at low pressure and when a high voltage of electricity is applied, some rays are generated from the cathode. He named these rays as cathode rays. When two charged plates are placed on either side of this discharge tube, these rays (cathode rays) are attracted to the positive plate. Hence he said that the cathode rays are made of negatively charged particles. He called these particles as ‘corpuscles’. Corpuscles mean particles. G. J. Stoney named them as ‘electrons’

In J.J. Thomson atomic model, the atom consists of a sphere of uniform distribution of positive charge with electrons embedded in it. The number of positive particles is equal to the number of electrons and the 'atom as a whole is eclectically neutral'. This model accounted for the neutrality of atom. This model is popularly known as"plum pudding model", like negatively-charged "plums" surrounded by positively-charged "pudding".

But later Rutherford proved that the electrons are not embedded in the positive sphere, but they revolve around the positive central core and he named it as nucleus

Molecular Formula for Alkynes

Introduction :

Alkynes are hydrocarbons which contains carbon-carbon triple bond. They show neither geometric nor optical isomerism. The simplest alkyne consist of one triple bond i.e. ethyne (HCCH) which is commonly termed as acetylene. The structural formula of acetylene is



Molecular Formula and Structural Formulas:

The alkynes consist of compounds which are based on carbon and hydrogen series containing leastways one triple bond. The alkyne is a homologous series having the formula of CnH2n-2, where n is any integer which is greater than one.

In the chain of long alkynes, the carbon atoms added are closed to each other via single covalent bonds. Each carbon atom in the alkynes is associated with sufficient hydrogen atom to complete the valency of carbon as four. In alkynes, if there are four or more than four carbon atoms, the triple bond can be situated in different positions next to the chain which results in the formation of isomers.

For example, the alkyne of molecular formulas C4H6 has two isomers,



As alkynes have restricted rotation because of the presence of triple bond, they do not hold stereo isomers as alkenes because there is sp hybridized bonding present in a carbon-carbon triple bond. The maximum separation is 180o between the hybridized orbitals in the sp hybridization so the molecule is in linear form. Thus the alkynes are located in straight line because of this stereo isomers are impossible.

Physical Properties of Molecular Formula for Alkynes:

Most of the alkynes are less dense than water but some are exceptions.

Chemical Properties of Molecular Formula for Alkynes;

Alkynes are more polar than alkanes and alkenes. Liquid alkynes are non-polar solvents so immiscible in water. Alkynes having low ratio of hydrogen atoms to carbon atoms are highly combustible.

These alkynes are highly reactive so can be easily broken into alkanes and alkenes. They store large amount of chemical energy that’s why highly exothermic when broken. The released heat can cause rapid expansion so care must be taken when managing with alkynes.

Conclusion on Molecular Formula for Alkynes:

The triple carbon bonds are formed in alkenes due to absence of hydrogen’s. Thus they allow carbon bonds to be stronger, because of the nucleus central force which pulls in nearby atoms.