Chemistry_Grade_10-12 (1).pdf

The facts are as follows there is an increasing world

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The facts are as follows: There is an increasing world population to feed Most soils in the world used for large-scale, intensive production of crops lack the necessary nutrients for the crops Conclusion: Fertilisers are needed! The flow diagram below shows the main steps in the industrial preparation of two important solid fertilisers. 455
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23.5 CHAPTER 23. THE CHEMICAL INDUSTRY - GRADE 12 Air Nitrogen Methane Hydrogen Haber process NH 3 H 2 SO 4 Fertiliser C Process Y NO Brown gas Liquid E Fertiliser D 1. Write down the balanced chemical equation for the formation of the brown gas. 2. Write down the name of process Y. 3. Write down the chemical formula of liquid E. 4. Write down the chemical formulae of fertilisers C and D respectively. The following extract comes from an article on fertilisers: A world without food for its people A world with an environment poisoned through the actions of man Are two contributing factors towards a disaster scenario. 5. Write down THREE ways in which the use of fertilisers poisons the environment. 23.5 Electrochemistry and batteries You will remember from chapter 17 that a galvanic cell (also known as a voltaic cell) is a type of electrochemical cell where a chemical reaction produces electrical energy. The emf of a galvanic cell is the difference in voltage between the two half cells that make it up. Galvanic cells have a number of applications, but one of the most important is their use in batteries . You will know from your own experience that we use batteries in a number of ways, including cars, torches, sound systems and cellphones to name just a few. 23.5.1 How batteries work A battery is a device in which chemical energy is directly converted to electrical energy . It consists of one or more voltaic cells, each of which is made up of two half cells that are connected in series by a conductive electrolyte. The voltaic cells are connected in series in a battery. Each cell has a positive electrode (cathode), and a negative electrode (anode). These do not touch each other but are immersed in a solid or liquid electrolyte. 456
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CHAPTER 23. THE CHEMICAL INDUSTRY - GRADE 12 23.5 Each half cell has a net electromotive force (emf) or voltage. The voltage of the battery is the difference between the voltages of the half-cells. This potential difference between the two half cells is what causes an electric current to flow. Batteries are usually divided into two broad classes: Primary batteries irreversibly transform chemical energy to electrical energy. Once the supply of reactants has been used up, the battery can’t be used any more. Secondary batteries can be recharged, in other words, their chemical reactions can be reversed if electrical energy is supplied to the cell. Through this process, the cell returns to its original state. Secondary batteries can’t be recharged forever because there is a gradual loss of the active materials and electrolyte. Internal corrosion can also take place.
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