1.1 What is Chemistry?

11.1. Chemical Equations http://www.ck12.org

Example 11.3

Substance A 2 reacts with substance B 2 to form substance AB 3. Write the balanced chemical equation for this
process.

Answer:

Write the general expression.

A 2 +B 2 →AB 3

Balance.

TABLE11.4: A

Reactants Products

A 2 2

B 6 6

Balancing Chemical Equations for Real Reactions

Now that we have studied the general process for describing and balancing chemical equations, we are going to
apply this approach to examples that include actual chemicals. As we present the following reactions, we are going
to focus only on the changes in composition from reactants to products. In later chapters, we will look at other
reaction properties, such as states of matter, temperature, and the energy lost or gained by a given reaction. In the
following lesson, we will look at ways to classify different types of reactions. This knowledge will allow us to make
reasonable predictions about the products that might be generated from a given set of reactants.

Tips for Balancing Equations

Before we get started with balancing chemical equations, here are some simple tips to consider:

1. If there are polyatomic ions that exist unchanged on both sides of the equation, it is often simpler to treat them
   as single units than to break them down into their individual elements.


2. It is often easier to leave elements that occur in their pure elemental form (on either side of the equation) for
   last.


3. If a reactant or product has a coefficient of 1, this number is not explicitly written.


4. In a correctly balanced equation, all coefficients must be whole numbers. However, the use of fractions can
   be helpful as a way of finding the correct coefficients. If all atoms in an equation are balanced but some have
   fractional coefficients, multiply all coefficients in the entire equation (including those not explicitly written!)
   by the lowest common denominator to get the final balanced equation.

Example 11.4

Liquid mercury is heated in the presence of oxygen to produce mercury(II) oxide. Write the balanced chemical
equation for this process.

Answer:

Start by writing the general expression.

Hg(l)+O 2 (g)→HgO(s)

Then, alter the coefficients to balance each element.