Power From the Nucleus
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Nuclear Fission
A Chain Reaction
Some large radioactive atoms can be made to behave in a different way. For example, an atom of uranium-235 splits into two separate atoms when it is struck by neutron. The splitting of an atom is called nuclear fission. Fission of a uranum-235 atom produce a krypton atom, barium atom and three neutron, as well as gamma rays. It also gives out a huge amount of heat energy.
When uranium-235 is struck by neutron, uranium split into barium and krypton and three neutron. Three neutron will be struck another uranium atom, to produce nine neutron and will be struck another uranium atom. A reaction that grows in this way called a chain reaction. This one is very fast. In only fraction of a second, enormous amounts of heat and radiation are produced.
The Atomic Bomb
The chain reaction above is the basis of the atomic bomb. In atomic bomb, the chain reaction builds up until its get out of control. Then the bomb explodes, giving out intense heat, a violent shock wave and deadly burst of radiation. The earth is scorched and burned for miles around, the air is poisoned, and the living thing are killed. The full effect of atomic bomb is not felt in a day, or even a week. The products of the explosion are radioactive, and some of them have long half-lives. They settle to the earth and slowly decay, causing radiation sickness, cancer and death.
The world's first atomic bomb was dropped on 
Hiroshima, in Japan, in August 1945. It probably contained about 10 kilograms of uranium. It killed 80 000 people within a day and 60 000 more died within a year. Nowadays, some countries possess bombs that are 5000 times more powerfull!!!
Electrochemical cells: Volta cells
Oxidation-reduction involve the transfer of electrons. The transfer of electrons between metals and metal ions is a common type of redox reaction. It's illustrates what happened when a strip of zinc is placed in a solution of copper(II) sulfate.In this reaction there is a transfer of electrons from the zinc metal to the copper(II) ions. The transfers of electrons from Zn to Cu2+ takes place on the surface of the zinc strip. As the reaction proceeds the zinc metal dissolves and copper metal is formed. As the Cu2+ ions are reduced to Cu metal the blue coloured solution fades, eventually becoming colourless. The Cu2+ ions have a greater tendency to gain electrons than Zn2+ ions. As a result, Cu2+ ions will accept electrons from atoms Zn metal, resulting in the formation of Cu atoms and Zn2+ ions.
This reaction illustrates how all redox reactions are the result of competition for electrons.
If a strip of copper is placed in a solution of zinc sulfate no reaction occurs. This is because Zn2+ ions have a lesser tendency to gain electrons than Cu2+ ions. As a result, Cu atoms will not give up electrons to Zn2+ ions.
Redox reactions can be used to generate electricity if the two half-reactions are
physically separated. The electrons which are transferred can then pass through an external wire or circuit rather than being transferred through direct contact. A redox reaction in which the reactants are physically separated so that the transferred electrons can be directed through an external circuit is called an electrochemical cell.
One of the earliest electrochemical cell was the Daniel cell, developed in 1835. This
cell was based on the reactions between metallic zinc and copper(II) sulfate reviously described. The only difference is that half-reactions are physically separated so that the transferred electrons can be directed through an external circuit. In this way usable electrical energy can be degenerated.
The Daniel cell was extensively used for many years in telegraph and telephone work
as a reliable source of electricity. This electrochemical cell can be demonstrated by partly immersing zinc and copper strips in 1 mol L-1 solutions of zinc sulfate and copper(II) sulfatemrespectively in separate containers. The solutions are joined by a salt bridge which consists of U-tube filled with an electrolyte solution such as potassium nitrate. Each of two parts, consisting of a metal strip in an electrolyte solution, is called a half-cell.
When the metal strips are connected with a piece of wire an electric current flows
through the circuit. If a voltmeter is connected across the metal strips the voltmeter should read 1.1 volts. As the cell operates, the zinc strip dissolves slowly, while the copper strip becomes coated with more copper. The blue colour of the copper(II) sulfate solution fades and the voltage gradually falls.
These observations can be explained in terms of oxidation and reduction processes. The zinc loses electrons to form zinc ions according to the following equation.
Zn(s) --> Zn2+(aq) + 2e-
The zinc ions go into solution and hence the zinc strip gradually dissolves. The electrons given up by the zinc pass through the external circuit to the copper strip. There they are accepted by copper(II) ions in the solution surrounding the copper strip. The copper(II) ions are reduced to copper atoms which deposit on the strip forming a copper layer. The equation is as follows.
Cu2+(aq) + 2e- --> Cu(s)
The removal of Cu2+ ions from the solution causes the blue colour of the solution to fade.
Each time two electrons are released by a zinc atom in the left-hand half-cell, two
electrons are accepted by copper(II) ion in the other half-cell. Thus, for each zinc ion produced, a copper(II) ion is removed from solution. Electrical neutrality in the half-cell solutions is maintained by the migration of positive ions towards the copper half-cell and negative ions towards the zinc half cell. Thus Zn2+ ions move into the salt bridge and K+ ions move into the copper half-cell. At the same time, SO4 2h ions from the copper half-cell move into the salt bridge while NO3 ions move into the zinc half-cell. Thus, the flow of current through the external circuit is by movement of electrons through a metallic wire conductor and the flow of current in the internal circuit is by movement of ions.
The cell will continue to generate an electric current until chemical equilibrium is
reached. In this reaction the reactants are almost completely converted to products before equilibrium is achieved. At equilibrium most of the copper(II) ions will have been lost from the solution and the concentration of the zinc ions will be nearly double the original 1 mol L-1. The voltage, ore.m.f., drops to zero at equilibrium.
Any electrochemical cell consists of two half-cells. Each half-cell consists of an
electrode, which is a conductive metal or graphite strip in contact with an electrolyte solution.
The electrode at which oxidation takes place is called the anode. As electrons are generated by oxidation, the terminal of the anode is marked as the negative (-). The electrode at which reduction takes place is called the cathode. Because electrons are accepted in reduction, the terminal of the cathode is marked as the positive (+).
When the anode and cathode are connected, an electric current flows through the
external circuit. This electron flow can be used as source of energy to heat a lamp filament, run a motor, operate a transistor radio and so on. In other words, chemical energy is being used to generate electrical energy. Electrochemical cells, in which chemical change is used to generate electrical energy, are also called galvanic or voltaic cells.
An electrochemical cell does not necessarily have reactive metal electrodes. Consider
the cell in Figure 19.5 in which the platinum electrodes are chemically inert. hydrogen and chlorine gases are bubbled over the surfaces of the platinum electrodes as shown. In this cell the half-cells share a common electrolyte which is 1 mol L-1 hydrochloric acid. When the external circuit is connected by a voltmeter an e.m.f. of 1.36 V register on the voltmeter.
This reaction illustrates how all redox reactions are the result of competition for electrons.
If a strip of copper is placed in a solution of zinc sulfate no reaction occurs. This is because Zn2+ ions have a lesser tendency to gain electrons than Cu2+ ions. As a result, Cu atoms will not give up electrons to Zn2+ ions.
Redox reactions can be used to generate electricity if the two half-reactions are
physically separated. The electrons which are transferred can then pass through an external wire or circuit rather than being transferred through direct contact. A redox reaction in which the reactants are physically separated so that the transferred electrons can be directed through an external circuit is called an electrochemical cell.
One of the earliest electrochemical cell was the Daniel cell, developed in 1835. This
cell was based on the reactions between metallic zinc and copper(II) sulfate reviously described. The only difference is that half-reactions are physically separated so that the transferred electrons can be directed through an external circuit. In this way usable electrical energy can be degenerated.
The Daniel cell was extensively used for many years in telegraph and telephone work
as a reliable source of electricity. This electrochemical cell can be demonstrated by partly immersing zinc and copper strips in 1 mol L-1 solutions of zinc sulfate and copper(II) sulfatemrespectively in separate containers. The solutions are joined by a salt bridge which consists of U-tube filled with an electrolyte solution such as potassium nitrate. Each of two parts, consisting of a metal strip in an electrolyte solution, is called a half-cell.
When the metal strips are connected with a piece of wire an electric current flows
through the circuit. If a voltmeter is connected across the metal strips the voltmeter should read 1.1 volts. As the cell operates, the zinc strip dissolves slowly, while the copper strip becomes coated with more copper. The blue colour of the copper(II) sulfate solution fades and the voltage gradually falls.
These observations can be explained in terms of oxidation and reduction processes. The zinc loses electrons to form zinc ions according to the following equation.
Zn(s) --> Zn2+(aq) + 2e-
The zinc ions go into solution and hence the zinc strip gradually dissolves. The electrons given up by the zinc pass through the external circuit to the copper strip. There they are accepted by copper(II) ions in the solution surrounding the copper strip. The copper(II) ions are reduced to copper atoms which deposit on the strip forming a copper layer. The equation is as follows.
Cu2+(aq) + 2e- --> Cu(s)
The removal of Cu2+ ions from the solution causes the blue colour of the solution to fade.
Each time two electrons are released by a zinc atom in the left-hand half-cell, two
electrons are accepted by copper(II) ion in the other half-cell. Thus, for each zinc ion produced, a copper(II) ion is removed from solution. Electrical neutrality in the half-cell solutions is maintained by the migration of positive ions towards the copper half-cell and negative ions towards the zinc half cell. Thus Zn2+ ions move into the salt bridge and K+ ions move into the copper half-cell. At the same time, SO4 2h ions from the copper half-cell move into the salt bridge while NO3 ions move into the zinc half-cell. Thus, the flow of current through the external circuit is by movement of electrons through a metallic wire conductor and the flow of current in the internal circuit is by movement of ions.
The cell will continue to generate an electric current until chemical equilibrium is
reached. In this reaction the reactants are almost completely converted to products before equilibrium is achieved. At equilibrium most of the copper(II) ions will have been lost from the solution and the concentration of the zinc ions will be nearly double the original 1 mol L-1. The voltage, ore.m.f., drops to zero at equilibrium.
Any electrochemical cell consists of two half-cells. Each half-cell consists of an
electrode, which is a conductive metal or graphite strip in contact with an electrolyte solution.
The electrode at which oxidation takes place is called the anode. As electrons are generated by oxidation, the terminal of the anode is marked as the negative (-). The electrode at which reduction takes place is called the cathode. Because electrons are accepted in reduction, the terminal of the cathode is marked as the positive (+).
When the anode and cathode are connected, an electric current flows through the
external circuit. This electron flow can be used as source of energy to heat a lamp filament, run a motor, operate a transistor radio and so on. In other words, chemical energy is being used to generate electrical energy. Electrochemical cells, in which chemical change is used to generate electrical energy, are also called galvanic or voltaic cells.
An electrochemical cell does not necessarily have reactive metal electrodes. Consider
the cell in Figure 19.5 in which the platinum electrodes are chemically inert. hydrogen and chlorine gases are bubbled over the surfaces of the platinum electrodes as shown. In this cell the half-cells share a common electrolyte which is 1 mol L-1 hydrochloric acid. When the external circuit is connected by a voltmeter an e.m.f. of 1.36 V register on the voltmeter.
Collision theory and activation energy
Although the factors affecting rates were discussed in the previous section, no consideration was given to what was actually happening at a molecular level during a reaction. The chemical equation for a reaction indicates the nature of the reactants and products but provides no information about the way in which thereactants are converted to products. For example, the decomposition of hydrogen iodide is represented by the following equation.2HI → H2 + I2
This equation indicates that for every two molecules of HI which decompose, one molecule of H2 and one molecule of I2 are produced. However, the equation does not indicate how HI molecules are converted to H2 and I2. The first step in a chemical reaction is thought to involve a collision between the reactant particles. This idea is part of the collision theory of reaction undergo an
appropriate collision.
From the kinetic theory, the particles in a gas are in a continuous state of random straight-line motion. While most of the particles have energies that are close to the average for all the particles in the system, a small fraction have energies much lower or much higher than the average. Because of this range of kinetic energies, collision between HI molecules will occur with differing energies. A collision between reactant molecules does not necessarily mean that a
reaction will take place. In fact, most collisions do not bring about a reaction. The collision theory requires that for a collision between reactant particles to lead to a chemical reaction the following conditions must be fulfilled.
1. The molecules must collide with sufficient energy to disrupt the bonds of the reactant molecules.
2. The molecules must collide with an orientation that is suitable for the breaking
For a reaction to occur between reactant molecules they must collide with a certain minimum energy. Unless this minimum collision energy is exceeded, the colliding molecules will simply rebound and move away from each other. The minimum energy that is required for a collision to result in a reaction is known as the activation energy for the particular reaction. Some reactions have relatively low activation energies and so react at a significant rate at room temperature. For these reactions, a noticeable reaction occurs as soon as the reactants are mixed. For example, a piece of sodium metal placed in water at room temperature produces a violent reaction almost instantaneously. Other reactions occur to an almost insignificant extent at room temperature. In such reactions the activation energy is so high that it is very unlikely that reactant molecules will collide with sufficient energy to undergo reaction. For example, methane will not react with oxygen unless the mixture is ignited. There is a relatively high activation energy for the reactions there would be in the order of 1010 collisions per second between
reactant molecules, virtually none of these would have sufficient energy for a reaction to take place.
As well as needing a minimum amount of energy, successful collisions also often have an orientation requirement. The relative orientations of the reactant molecules during a collision must be favorable for the breaking of particular bonds in the reactants and the formation of new bonds in the products. This factor also contributes to the fact that many collisions between reactants are unsuccessful in producing a reaction.
appropriate collision.
From the kinetic theory, the particles in a gas are in a continuous state of random straight-line motion. While most of the particles have energies that are close to the average for all the particles in the system, a small fraction have energies much lower or much higher than the average. Because of this range of kinetic energies, collision between HI molecules will occur with differing energies. A collision between reactant molecules does not necessarily mean that a
reaction will take place. In fact, most collisions do not bring about a reaction. The collision theory requires that for a collision between reactant particles to lead to a chemical reaction the following conditions must be fulfilled.
1. The molecules must collide with sufficient energy to disrupt the bonds of the reactant molecules.
2. The molecules must collide with an orientation that is suitable for the breaking
For a reaction to occur between reactant molecules they must collide with a certain minimum energy. Unless this minimum collision energy is exceeded, the colliding molecules will simply rebound and move away from each other. The minimum energy that is required for a collision to result in a reaction is known as the activation energy for the particular reaction. Some reactions have relatively low activation energies and so react at a significant rate at room temperature. For these reactions, a noticeable reaction occurs as soon as the reactants are mixed. For example, a piece of sodium metal placed in water at room temperature produces a violent reaction almost instantaneously. Other reactions occur to an almost insignificant extent at room temperature. In such reactions the activation energy is so high that it is very unlikely that reactant molecules will collide with sufficient energy to undergo reaction. For example, methane will not react with oxygen unless the mixture is ignited. There is a relatively high activation energy for the reactions there would be in the order of 1010 collisions per second between
reactant molecules, virtually none of these would have sufficient energy for a reaction to take place.
As well as needing a minimum amount of energy, successful collisions also often have an orientation requirement. The relative orientations of the reactant molecules during a collision must be favorable for the breaking of particular bonds in the reactants and the formation of new bonds in the products. This factor also contributes to the fact that many collisions between reactants are unsuccessful in producing a reaction.
Label:
The Effect of ChangingThe Temperature of Equilibrium System
The effect of changing the temperature of equilibrium system can be predicted from a knowledge of the heats of reaction. If the temperature of a system is lowered, the exothermic reaction is favoured. If the temperature isincreased, the endhotermic reaction is favoured.
For the N2O4/NO2 system the forward reaction is endothermic.N2O4 + 57 kJ <===> NO2
The forward reaction therefore absorbs heat from the surroundings and the reverse reaction releases heat to the surroundings. According to Le Chatelier’s principle, if the temperature of an equilibrium system is increased the system will adjust to re-establish equilibrium in such a way as to decrease the temperature. Therefore in re-establishing equilibrium the endothermic reaction is favoured as this absorbs heat from the surroundings and would tend to decrease the temperature. In the N2O4/NO2 system this would result in an increase in the concentration of NO2 and a decrease in the cpncentration of N2O4.
If the temperature of the equilibrium system was reduced the system would re-establish equilibrium by favouring the exothermic reaction. This would tend to increase the temperature of the surroundings, partially counteracting the change. In the N2O4/NO2 system, more N2O4 and less NO2 would be present when equilibriuym was re-established.
If the temperature of the equilibrium system was reduced the system would re-establish equilibrium by favouring the exothermic reaction. This would tend to increase the temperature of the surroundings, partially counteracting the change. In the N2O4/NO2 system, more N2O4 and less NO2 would be present when equilibriuym was re-established.
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