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My Pages On Different Subjects which Hyperlinked to all my Blog Posts

Sunday, 17 June 2012

Thermochemistry : Catalysis : Properties of Water.


Thermochemistry Page from my Chemistry-World software


















































Thermochemistry:

Thermochemistry primarily deals with the transfer of the heat between a chemical system and its surroundings when a reaction of a phase change takes place within the system. The heat transfer is basically due to the conservation of energy or first law of thermodynamics. Heat transfer can take place under law of thermodynamics we know that the heat transferred at constant volume changes the internal energy of the system whereas that at constant pressure changes the enthalpy of the system, in the laboratory, the majority of chemical reactions are carried out under the condition of constant pressure, and thus the heat transferred in such a system is equal to the enthalpy changes in a chemical reaction. Since the enthalpy of a system can also change due to the variation of temperature and pressure, it is therefore essential that the reactants and products in a chemical reaction must have the same temperature and pressure.

Enthalpy change of a Chemical equation:

Two types of reactions may be distinguished.

Nitroglycerine is burst out in presence f air and produces nitrogen, oxygen, Carbon dioxide and water. Heat of the reactant(Nitroglycerine) is much higher than the heat of the products (Nitrogen, oxygen, Carbon dioxide, water), therefore reactant(Nitroglycerine) energy is much higher than the end products(Nitrogen, oxygen, Carbon dioxide, water), energy.


1)Exothermic reaction:
  For these (^H) is negative which implies negative qp and hence release of heat when reactants are converted into products in this case . Example: Nitroglycerine is burst out in presence f air and produces nitrogen, oxygen, Carbon dioxide and water. Heat of the reactant(Nitroglycerine) is much higher than the heat of the products (Nitrogen, oxygen, Carbon dioxide, water), therefore reactant(Nitroglycerine) energy is much higher than the end products(Nitrogen, oxygen, Carbon dioxide, water), energy.

Heat of Product(H) < Heat of Reactant(H) (Initial Reactant heat is greater than the product heat)

Iron wool is heated in presence of chlorine gas produces solid iron chloride. Temperature of iron chloride (end product) is much higher than iron wool and chlorine gas(reactant). In this reactions end product`s(Iron Chloride) energy is higher than the reactant energy(Iron wool and chlorine gas)

2) Endothermic Reaction:
For These heat(^H) is positive which implies positive qp and hence absorption of heat when reactants are converted into products. Example: Iron wool is heated in presence of chlorine gas produces solid iron chloride. Temperature of iron chloride (end product) is much higher than iron wool and chlorine gas(reactant). In this reactions end product`s(Iron Chloride) energy is higher than the reactant energy(Iron wool and chlorine gas)

Heat of Product(H) > Heat of reactant(H) (End product heat is greater than the initial reactant heat)


video
                                                                                       3D animation showing Endo and Exo Thermic Reactions with energy and reaction speed Graph.


Catalysis Page from my Chemistry-World software

Catalysis:

Catalysis is the acceleration of a chemical reaction by means of a substance called catalyst, which is added to the reaction but remains unchanged after the reaction has occurred. A catalyst speeds up a reaction by lowering the amount of energy required to initiate the reaction. Why use catalyst? There are some chemical reactions that can be easily accelerated, for example by increasing the temperature may result in the destruction of important proteins. Catalysts provide an alternative means of achieving the same result.

Catalyst Graph showing "Activation Energy"


Lowering the Activation energy:

For a chemical reaction to occur there must be sufficient energy to initiate it.This energy threshold is called the "activation energy" . The purpose of catalyst is to lower the activation energy required to initiate a chemical reaction, thereby speeding by adding a catalyst can happen in a number of ways.For example, the catalyst may alter the structure of the reactant, allowing it to react more readily, or the catalyst might hold the reactant molecules in a particular orientation, which reduces the amount of energy that is required for the reaction. Either way, it is important to remember that catalyst remain unchanged after the chemical reaction occurs.

Catalyst Graph Showing energy difference

Yet this is not to say that catalyst does not participate in the chemical process-- in fact, there are many catalysts that work by breaking down the reaction process by creating intermediate compounds. Typically, these intermediate compounds are unstable, and a second reaction occurs,producing the desired end products, and returning the catalyst to its original form. For this reason catalyst are recyclable, and can be used many times, making them incredibly useful for industrial applications.Ferric or Iron chloride is used widely as a catalyst in various industrial applications.

Catalytic Converter:

First introduced to the automotive industry during the 1970s, the catalytic converter uses the principle of catalyst to help reduce the toxic emissions that are produced by car engines.

Automotive Vehicles catalytic converters

There are two types of catalytic converters- Two way and three way catalytic converters. Each of this converters performs a similar task, and their function can be explained chemically according to a few simple reduction and oxidation reactions. 

video
                                                                       3D animation showing effect of catalytic converter in Automobile which turns black smoke into clear white.
 

a two way catalytic converter results in two outcomes,first it performs the oxidation of carbon monoxide (a highly toxic substance) to carbon dioxide.

2CO + O2 = 2CO2

It as results in the oxidation of any unburnt hydrocarbons (Left over from the internal combustion of fuel), resulting in the production of carbon dioxide and water.

2CxHy + 2(2x + y/2) O2 = 2xCO2 + yH2O

The Three way catalytic converter goes no extra step to reduce nitrogen oxides to nitrogen and oxygen.

2NOx =  xO2 + N2

The catalyst that is used in a automotive catalytic converters is most often a precious metal.In most cases platinum is used , because of its high level of activity , however other precious metals can also be used, such as rhodium, palladium, iron, copper , nickel and manganese.

Water Properties Page from my Chemistry-World software

Properties of Water:

 Water is most common compounds on earth, but it is also one of the most unusual. Water is only compound that naturally exists in three states of matter n earth`s surface and the only compound to become less dense when it changes from liquid to solid. 

Clear Water


We depend on the unique chemical and physical properties of water for all life as we know it.The molecule of water consist of two hydrogen atoms covalently bonded t an oxygen atom. Water for all life as we know it. The molecule of water consist of two hydrogen atoms covalently bonded to an oxygen atom. Water is a tasteless, colorless. odour less liquid at room temperature and pressure. 

Liquid and Gas or vapour  Form of Water


Water is found on earth as solid ice and liquid water and water vapour. It will readily change state according to temperature and pressure changes, for example, the ice in glass will melt on a warm day and water droplets from your breath will quickly evaporate. Water can also change directly from a gas to a solid when frost is formed and from a solid to a gas.

The temperature and pressure at which all three states of water can coexists is knows as a triple point and occurs almost exactly at 32 degree F (o degree C) at sea level ( 1 Atmosphere). Under this condition it is possible for water to change from ice, liquid water or vapour as a result of infinitely small changes in pressure and temperature.On the other hand, if you increase the pressure, 

As in a pressure cooker, water will be at a higher temperature.


as in a pressure cooker, water will be at a higher temperature. If the temperature of earth were not as it is, for example if earth were closer t or further from the sun, then we would not have the vast quantities or solid, liquid and gaseous water that we have n our planet.

When Water freezes:  the molecule arrange themselves differently so that frozen water become less dense and also expands by up to o% volume.


video
3D animation showing that upper part of the frozen pond where people are walking and under the icy layer Fishes are swimming comfortably under water.

When Water freezes:  the molecule arrange themselves differently so that frozen water become less dense and also expands by up to o% volume. This is one of the reasons why ice floats n top of water. Water freezes at 32 degree F into ice and become less denser than water. Less dense ice therefore floats above the water of the pond and thus fishes and other aquatic animals of the pond swim on the lower liquid water of the pond .For that reason the temperature gradually increases with the increase of the depth of the pond.

Water freezes at 32 degree F into ice and become less denser than water. Less dense ice therefore floats above the water of the pond and thus fishes and other aquatic animals of the pond swim on the lower liquid water of the pond

The Bond within a water molecule:

The chemical bonds that hold a water molecule (H2O) together are important in giving water the shape and structure that makes it s useful. Oxygen has higher electronegativity than hydrogen, which means that it will have a stronger attraction for electrons in the O---H bonds than hydrogen. This difference of electronegativity results in a intramoleculer charge difference, with the oxygen part of the molecule being negatively charged and hydrogen is positively charged. The small positive hydrogen nuclei will be exposed, which allows for the formation of unique intermolecular force, the hydrogen bond.

Hydrogen Bond Within Water



Hydrogen bonds, which give water many of its special properties, form between the negatively charged oxygen atom in one molecule and the small, positive hydrogen atoms in a neighbouring molecule Hydrogen bonds are the cause of the high boiling point, melting point, surface tension, and viscosity f water, and the lower density water compared with liquid water.

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