What is the difference between a physical and chemical change?

What are the 4 phases of matter in order of increasing engery content?

Sodium nitrite (nano2) reacted with 2−iodooctane to give a mixture of two constitutionally isomeric compounds of molecular formula c8h17no2 in a combined yield of 88%. draw reasonable structures for these two isomers. click the "draw structure" button to launch the drawing utility. place the two compounds in the appropriate boxes below.

What is the chemical formula for dihydrogen monoxide