hello students today we are going to start 1 chapter of class 11 chemistry so we will study the first chapter of chemistry which is basic concepts of chemistry In this, we see why chemistry is important and which chemical we use and what are the significant how it helps us in many ways what is a significant figure what is an element what is mixture all these basic we will not do which is some basic parts of chemistery we will tell you what is a chemical combination and we will tell you that what is the law of combination so the laws of chemical combination we will study today there are 5 big laws in chemistry yes there are 5 big laws who decide how the element will combine and form compound {repeated} so a mass of one element form compound form with other elements in which percentage it will react in how many moles which gas will divide in which ratio all these things are decide by 5 laws says laws of chemical combination so we will start laws of combination and the first and first law is studied by all law of conservation of mass law of conservation of mass so I tell these all things were discovered in the 1740s and 1780s it means all these concepts are too old so no new laws will be added so the law of conservation says that in chemistry when two compounds are combined they form a new compound so the mass of two compounds on one side is equal to newly formed compound that means mass can be neither be created nor be destroyed the mass of two compounds on one side is equal to newly formed compound means the sum of the mass of reactants should be equal to the sum of the mass of products it is too basic still I want that you will make notes of these concepts put a heading law of chemical combination and start note making so 1 law is sum of the mass of reactants should be equal to the sum of the mass of products so we start this story with examples carbon combined with oxygen to give carbon dioxide this reaction is balanced 1 carbon and 2 oxygen the atomic mass of carbon is 12 and mass oxygen is 16 see how many carbons are there is 12 and oxygen is 16 multiply 2 is 32 and how carbon dioxide will form 12+16 multiply by 2 it becomes 44 do sum of these 2 it becomes 44 and another side also it is 44 the sum of the mass of reactant is equal to the sum of the mass of product so it is not a big thing it is too simple everybody knows that when a chemical reaction occurs the sum of the mass of reactant is equal to the sum of the mass of product applied nowadays it is not applicable because you all know that there are some reactions in which E=MC^2 IS applied and some mass released in the forms of energy but these are very old laws and in that time these things were no discussed so buddy question arises we come with a question let see you are able to do or not first question is good and the question is 1.5 gram of ethane 1.5 gram of ethane on complete combustion gives 44 gram of carbon dioxide and 2.7 gram of H2O SHOW THAT the reaction obeys law of conservation of mass so you have to prove this reaction follows the law of conservation of mass so we need to write a reaction