DECOMPOSITION OF COMPOUNDS. 



51 



QUESTIONS. 



61. What are the three principal methods used for the determination 

 of atomic weights ? 



62. Why are chemical means not always sufficient to determine 

 atomic weights ? 



63. How can the specific gravity of elements in the gaseous state be 

 used for the determination of atomic weight ? 



64. Describe a method of the determination of atomic weight by 

 chemical means. 



65. State one of the reasons why the atomic weight of oxygen has 

 been changed from 8 to 16. 



66. What relation exists between atomic weight and specific heat ? 



67. State the Law of Dulong and Petit. 



68. Suppose the specific heat of an element to be 0.1138, what will 

 its atomic weight be? 



69. Suppose the specific gravity of an elementary gas to be 14, what 

 will its atomic weight be ? 



70. Suppose 216 grams of an element replace 2 grams of hydrogen 

 in 73 grams of HC1, what will the atomic weight of the element be ? 



DECOMPOSITION OF COMPOUNDS. 

 COMPOUNDS. 



GROUPS OF 



Action of heat upon compounds. All phenomena taking place 

 in nature are, without exception, due to motion. Chemistry 

 considers the motion of atoms, without which no chemical 

 change takes place. The causes for chemical changes are either 

 physical actions (heat, electricity), or the decomposing influence 

 of one substance upon another substance in consequence of 

 greater affinity between them under given conditions. 



The decomposing action of heat upon compounds has been 

 mentioned before in connection with the decomposition of red 

 oxide of mercury into mercury and oxygen. Similarly to this 

 process, many other compound substances are decomposed by 

 heat either into elements, or, more frequently, into simpler 

 forms of combination. This means that the molecule of a sub- 

 stance containing, for instance, 10 atoms, is split up into 2, 3, 

 or more molecules, each one containing a portion of the 10 

 atoms. 



