Laws of chemical combination


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Laws of chemical combination

  1. 1. Dr. A.K. Gupta 1
  2. 2. All the Chemical reactions take place according to the certain Laws.These are called ‘Laws of Chemical combination”.The various Laws of Chemical combination are :-1. Law of Conservation of Mass.2. Law of Multiple Proportions.3. Law of Constant Composition.4. Law of Reciprocal Proportions.5. Gay Lussac’s law of Gaseous Volumes. (Law of Combining Volumes) The first Four laws are related to the mass relationships while the fifth one Deals with the volume of the reacting gases. Let us see what these Laws are. 2
  3. 3. Given By : Antoine Lavoisier, in the year 1774.In all Physical and Chemical changes, the total mass of the reactants is equal to that of the products.In other words …Matter can neither be created nor destroyed.Hence the Law is also called as The Law of indestructibility of Matter. 3
  4. 4. To prove this Landlot took NaCl in one limb of Landlot’s tube, and AgNO3in the other .Then he mixed the two solutions by inverting the tube. AgCl + NaNO3 NaCl AgNO3 NaCl + AgNO3 NaNO3 + AgCl (23+35.5) +(108+14+48) (23+14+48) + (108+35.5) 228.5 = 228.5 4
  5. 5. Given by: John Dalton in the year 1804When two elements combine to form two or morechemical compounds, then the weights of one of theelements which combines with a fixed weight of theother, bear a simple ratio to one another.For example Nitrogen and Oxygen combine with eachother to form following compounds:N2O, NO, N2O3, N2O4, N2O5 5
  6. 6. Compounds Nitrous Nitric Nitrogen Nitrogen Nitrogen Oxide Oxide Trioxide Tetra oxide Pent oxideElementsFormula N2O NO N2O3 N2O4 N2O5Wt. of 28 14 28 28 28NitrogenWt. of 16 16 48 64 80OxygenWhen N is 14 14 14 14 14taken 14Then O is 8 16 24 32 40 The simple ratio of Oxygen which combines with fixed amount of Nitrogen (14 in this example) is 1:2:3:4:5, which is a simple ratio. 6
  7. 7. Given by: J.L. Proust in the year 1799.A Chemical Compound is always found to be made up ofthe same elements combined together in the same fixedproportion by weight.For example pure Carbon dioxide obtained from whatever source (Heating CaCO3or burning carbon, or by reacting MgCO3 with HCl), will always be made up of12 parts of Carbon and 32 parts of Oxygen by weight. 7
  8. 8. Given by: Richter, in the year 1792.The ratio of the weights of two elements A and B whichcombine separately with a fixed weight of the third elementC is either the same, or some simple multiple, of the ratioof the weights, in which A and B combine directly witheach other. To understand this better, let us assume that A is Carbon, B is Oxygen, and C is Hydrogen . 8
  9. 9. Remember: A is Carbon, B is Oxygen, and C is Hydrogen.Carbon and Oxygen combine with Hydrogen to form CH4 andH2O respectively. In CH4, 4 gram H combine with 12 gramCarbon, while in H2O, 2 gram Hydrogen combine with 16 gramOxygen or 4 gram H will combine with 32 gram O.Thus the ratio of C:O which combine with 4 gram of His 12:32 or 3:8Now C and O combine directly with each other to form CO2and the ratio of their weights is 12:32 or 3:8, which is same asthat with Hydrogen. 9
  10. 10. Ratio 4:12H H HH H H Ratio2:16 or 4:32 Ratio 12:32 10
  11. 11. Given by: Gay Lussac in the year 1808.When gases react together, they always do so in volumeswhich bear a simple ratio to one another and to thevolumes of the products, provided all measurements ofvolumes are done under similar conditions of temperatureand pressure. Reactions Ratio N2 + 3 H2 2 NH3 1:3:2 2 H2 + O2 2 H2O 2:1:2 H2 + Cl2 2 HCl 1:1:2 11
  12. 12. APresentation ByDr. A.K. Gupta 12