274 ELEMENTARY GENERAL SCIENCE CHAP. 



so that the molecular weight of a gas is double its density 

 (referred to hydrogen). 



Chemical Actions Represented by Equations. We will 

 now give a number of equations to represent some of the 

 chemical reactions we have studied. In all the cases the 

 quantitative relation should be found and written down. The 

 decomposition of potassium chlorate by heat is represented by : 



2KC1O 3 = 2KC1 + 3O 2 , or 



2x122-5 ( = 39 + 35-5 + 48) "2x74'5 ( = 35*5 + 39) 



parts by weight of will yield parts by weight of 

 potassium chlorate potassium chloride 



with 3 x 32 parts by weight of oxygen. 



The burning of sodium, carbon, phosphorus, and sulphur are 

 respectively represented by : 



; = C0 2 



P 4 + 5O 2 =2P 2 O 5 . 



(Write these also in words and, using the atomic weights on 

 page 275, give the weights of the substances taking part in the 

 reactions as is done in the above example.) 



The displacement of hydrogen from water or acids, is given by 

 the equations : 



2H 2 O + Na 2 = 2NaOH + H 2 . 



It will be noticed that according to the first equation, only 

 one half the hydrogen is eliminated from water by sodium, and 

 it may be shown that caustic soda still contains hydrogen. 



The formation of sulphur dioxide is more complicated : 



Cu + 2H 2 S0 4 = CuS0 4 + S0 2 + 2H 2 O ; 



that is, copper forms with sulphuric acid copper sulphate, sulphur 

 dioxide, and water ; while the formation of sulphur trioxide and 

 sulphuric acid are very simply shown : 



(1) 2SO 2 + O 2 = 2S0 3 . 



The sulphide of iron we have used is represented by FeS (the 

 symbol Fe standing for iron, ferrum), and the reaction of the 

 sulphide with sulphuric acid by the equation : 



FeS + H 2 SO 4 --= FeSO 4 + SH 2 . 



