what are some chemical reactions
1 Direct Combination or Synthesis Reaction. 2  In a synthesis reaction two or more chemical species combine to form a more complex product. 3  A + B â AB. 4  The combination of iron and sulfur to form iron (II) sulfide is an example of a synthesis reaction : An acid-base reaction is type of double displacement reaction that occurs between an acid and a base. 2  The H + ion in the acid reacts with the OH-ion in the base to form water and an ionic salt: 3  HA + BOH â H 2 O + BA. 4  The reaction between hydrobromic acid (HBr) and sodium hydroxide is an example of an acid-base reaction: