Más contenido relacionado


Chapter 1 class 10 (2).pdf

  1. Introduction
  2. Activity 1.1
  3. Activity 1.1
  4. • magnesium ribbon burns with a dazzling white flame and changes into a white powder. • This powder is magnesium oxide. • It is formed due to the reaction between magnesium and oxygen present in the air.magnesium, etc. Activity 1. 1
  5. Activity 1.2
  6. Activity 1.2
  7. Activity 1. 3
  8. Activity 1. 3
  9. Activity 1. 3
  10. From the above three activities, we can say that any of the following observations helps us to determine whether a chemical reaction has taken place – • Change in state • Change in colour • Evolution of a gas • Change in temperature. Conclusion
  11.  A chemical reaction is a process where the reactant gets converted into a product which may be under an influence of a catalyst .  A word-equation shows change of reactants to products through an arrow placed between them. What are chemical reactions ?
  12.  The reactants are written on the left-hand side (LHS) with a plus sign (+) between them. Similarly, products are written on the right- hand side (RHS) with a plus sign (+) between them.  The arrowhead points towards the products, and shows the direction of the reaction. What are chemical reactions ?
  13. What are chemical reactions ?
  14. Writing a chemical reaction  A chemical equation represents a chemical reaction. If you recall formulae of magnesium, oxygen and magnesium oxide, the above word-equation can be written as – Mg+O2 →MgO
  15.  A chemical reaction is identified by any of these 4 factors Change in state  change in colour  evolution of a gas  Change in temperature.  According to law of conservation of mass matter can neither be created nor be destroyed in a chemical reaction. ANTOINE LAVOISER INTRODUCED LAW OF CONSERVATION OF MASS How do we identify a chemical reaction?
  16. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.  In other words, the number of atoms of each element remains then same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation Balancing a chemical reaction
  17. Balancing a chemical reaction
  18.  To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.  List the number of atoms of different elements present in the unbalanced equation  Start balancing with the compound that contains the maximum number of atoms. It may be a reactant or a product. In that compound, select the element which has the maximum number of atoms. Balancing a chemical reaction
  19.  Balance the unbalanced atom.  Finally, to check the correctness of the balanced equation, we count atoms of each element on both sides of the equation.  To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s), respectively.
  20.  The word aqueous (aq) is written if the reactant or product is present as a solution in water.
  21. Balancing a chemical reaction
  22. Balancing a chemical reaction
  24. When two or more substances (elements or compounds) combine to form a single product, the reactions are called combination reactions A reaction in which a single product is formed from two or more reactants is known as a combination reaction. COMBINATION REACTIONS
  26.  Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat. CaO + H2O > Ca(OH)2 Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3. COMBINATION REACTIONS
  27.  Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.  Burning of natural gas and the decomposition of vegetable matter into compost are also an example of an exothermic reaction.
  28.  Endothermic reaction are those reactions in which heat is absorbed.  During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. So Exothermic process S
  29. Decomposition reactions  When a product breaks up into its constituent reactants the reaction is termed as decomposition reaction. Heat 2FeSO4 (s) >Fe2O3(s) + SO2 (g) + SO3 (g)  In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferrous sulphate crystals (FeSO4, 7H2O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.  Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition. TYPES OF CHEMICAL REACTIONS
  30. • Metals are described as chemical elements that readily lose valence electrons to form positive ions (cations). Examples: Aluminium, copper, iron, tin, gold. • Around 90 of the total 118 elements are metals. Metals
  31. The property of metals by which they can be beaten into thin sheets is called malleability. Malleability
  32. The property of metal by which it can be drawn into wires is called ductility. Ductility
  33. Metals produce ringing sounds, they are said to be sonorous. The materials other than metals are not sonorous Sonorous
  34. ● Hard and have a high tensile strength ● Solids at room temperature, except mercury, which is liquid at room temperature. ● Sonorous ● Good conductors of heat and electricity ● Malleable, i.e., can be beaten into thin sheet Physical Properties of Metals
  35. ● Malleable, i.e., can be beaten into thin sheets ● Ductile, i.e., can be drawn into thin wires ● High melting and boiling points (except Cesium (Cs) and Gallium (Ga)) ● Dense, (except alkali metals). Osmium – highest density and lithium – least density ● Lustrous ● Silver-grey in colour, (except gold and copper) Physical Properties of Metals
  36. • Non-metals are those elements, which do not exhibit the properties of metals. Examples: Carbon, Boron, etc. Non-Metals
  37. • Materials like coal and sulphur are soft and dull in appearance. • They break down into a powdery mass on tapping with a hammer. • They are not sonorous and are poor conductors of heat and electricity.bThese materials are called non-metals. • The examples of non-metals are sulphur, Carbon, oxygen, phosphorus, etc. Non-metals
  38. • The name of the product formed in the reaction of sulphur and oxygen is sulphur dioxide gas. • When sulphur dioxide is dissolved in water sulphurous acid is formed. • The reaction can be given as follows: Sulphur dioxide + Water →Sulphurous acid SO2 + H2O  H2SO4 • The sulphurous acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature. Reaction of Non-Metals with oxygen.
  39. Reaction with Water You observed that sodium reacts vigorously with water. Some other metals do not do so. For example, iron reacts with water slowly.
  40. Reactions with Bases • What does the ‘pop’ sound indicate? • As before, the ‘pop’ sound indicates the presence of hydrogen gas. • Metals react with sodium hydroxide to produce hydrogen gas.
  41. • Many non-metals react with bases to form salts. • Bases are electron donors whereas non-metals are electron acceptors. Thus, bases donate electrons to non-metals which readily accepts them and form a salt. • Reactions of non-metals with bases are complex.