1.1 What is Chemistry?

http://www.ck12.org Chapter 11. Chemical Reactions

TABLE11.5: 2Hg(l)+O

Reactants Products

Hg 2 2

O 2 2

Notice that in this example, the formula for oxygen is the diatomic form O 2. Many pure nonmetallic elements
are unstable as individual atoms and combine readily to make diatomic molecules. Hydrogen (H 2 ), nitrogen (N 2 ),
oxygen (O 2 ), and the halogens (F 2 , Cl 2 , Br 2 , and I 2 ) exist as diatomic molecules when in their pure elemental forms.

Example 11.5

Hydrogen gas and fluorine gas react to form hydrogen fluoride gas. Write the balanced chemical equation for this
process.

Answer:

Start by writing the general expression.

H 2 (g)+F 2 (g)→HF(g)

Then balance each element.

TABLE11.6: H

Reactants Products

H 2 2

F 2 2

Again, pure hydrogen and fluorine exist as diatomic gases.

Example 11.6

Ammonium nitrate decomposes to form nitrogen gas, water, and oxygen gas. Write the balanced chemical equation
for this process.

Answer:

Write the general expression.

NH 4 NO 3 (s)→N 2 (g)+H 2 O(l)+O 2 (g)

Balance.

Because this equation involves more than two elements, it is slightly less straightforward to balance. Since nitrogen
and oxygen both occur in their pure elemental forms, we start by balancing hydrogen:

NH 4 NO 3 (s)→N 2 (g)+2H 2 O(l)+O 2 (g)

Hydrogen and nitrogen are now balanced, but oxygen is not. This can be fixed by changing the coefficient on its
pure elemental form:

NH 4 NO 3 (s)→N 2 (g)+2H 2 O(l)+^12 O 2 (g)

The atoms are now balanced, but to avoid having fractional coefficients, we must multiply all coefficients in the
equation by 2: