Physical or Chemical ?

Question

How can I tell if the equations are Physical or Chemical ?

 

A) C₇H₈N₄O₂(s) = C₇H₈N₄O₂(l)

 

B)NaOCl(aq) + 2NH₃(aq) = N₂H₄(l) + NaCl(aq) +H₂O(l)

Answer 1

All changes of state are physical changes only.  If ice melts for example, it is still H₂O.  Your first equation is thus a physical change (whatever that is, it is melting).

 

The second one though is creating N₂H₄ when previously there was none.  This is a chemical change, as the nitrogen was previous part of the NH₃, which was rearranged into new products.