Exercise 2 solution

All four equations were atom-counted in Python and are balanced.

(a) 2H2O2 -> 2H2O + O2: decomposition. One substance breaks into simpler ones; the
    Chemical reaction article's phrase is "a more complex substance breaks down into
    its more simple parts". (The type is my classification (check).)
(b) CH4 + 2O2 -> CO2 + 2H2O: combustion. A compound reacts with oxygen, matching "an
    element or compound reacts with an oxidant, usually oxygen". This equation is given
    on the Combustion and Chemical equation pages.
(c) 2HCl + 2Na -> 2NaCl + H2: single displacement. Sodium, an uncombined element,
    takes the place of hydrogen in the compound: "a single uncombined element replaces
    another in a compound". The equation is from the Chemical equation article; the
    label is mine (check).
(d) AgNO3 + NaCl -> AgCl + NaNO3: double displacement. The ions swap partners: "the
    anions and cations of two compounds switch places and form two entirely different
    compounds". (My example and classification (check).)

Overlap: the labels are not exclusive. (a) ends up with a simple substance as well as
water, yet it is still one substance breaking down. (b) is combustion only; it is not a
synthesis since the products are two compounds. Burning hydrogen would be both
synthesis and combustion (my reading (check)).