In the reaction 2 HgO(s) — 2 Hg(s) + O2(g)
how many liters of oxygen gas, O2, measured at STP are produced from the decomposition of 287 g of mercury(II) oxide,
HgO?

(+)(+)=+++.
(
a
+
b
)
(
c
+
d
)
=
a
c
+
a
d
+
b
c
+
b
d
.

It’s counterproductive because it only applies to products of binomials. It doesn’t help for expanding (++)(+)
(
a
+
b
+
c
)
(
d
+
e
)
or even (+).
a
(
b
+
d
)
.
It would be better if students learned the general distributivity law: to expand the product of two sums of any number of terms, take all the products of terms in the first times terms in the second and sum them together. For example,

(++)(+)=+++++.
(
a
+
b
+
c
)
(
d
+
e
)
=
a
d
+
a
e
+
b
d
+
b
e
+
c
d
+
c
e
.

It includes the product of two binomials as a special case.

The answer is c. 320 g