CHAPTER 11: CHEMICAL

REACTIONS Mrs. Brayfield

WRITING EQUATIONS

Write the chemical equation for the following:

Magnesium metal reacts with hydrochloric acid to

form aqueous magnesium chloride and hydrogen gas

Mg s + HCl aq → MgCl2 aq + H2(g)

Sulfur burns in oxygen to form sulfur dioxide

S s + O2(g) → SO2(g)

CHEMICAL REACTIONS

What is a chemical reaction?

It is where one or more things changes

What are examples of chemical reactions?

How can we describe what happens in chemical

reactions?

Reactants → Products

CHEMICAL EQUATIONS

A chemical equation is a representation of a

chemical reaction

For example the reaction between iron and oxygen:

Fe + O2 → Fe2O3

A skeleton equation is a chemical equation that

does not indicate the relative amounts of the

reactants and products

SYMBOLS IN CHEMICAL EQUATIONS

(on page 348)

BALANCING CHEMICAL EQUATIONS

When we look at the skeletal equation for a bike:

We don’t see the relative amounts of each part.

This is called an unbalanced equation

F + 1W + H + 1P → FW2HP2

BALANCING CHEMICAL REACTIONS

The balanced equation for a bike would be:

The balanced equation is where each side of the

equation has the same number of atoms of each

element

F + 2W + H + 2P → FW2HP2

BALANCING CHEMICAL EQUATIONS

The small whole numbers in front of the formulas

to balance the equation are called the coefficients

F + 2W + H + 2P → FW2HP2

BALANCING CHEMICAL REACTIONS

So there are three steps when balancing chemical

reactions:

1. Write the skeleton equation

2. Use coefficients to balance the equation

3. Make sure that there are the same number of

atoms of each element on both sides of the

equation

BALANCING CHEMICAL REACTIONS

The following reactions are balanced:

C(s)

Carbon + O2(g)

Oxygen CO2(g)

Carbon dioxide

TYPES OF REACTIONS

In Chemistry we can classify reactions into five

general types:

1. Combination Reaction

2. Decomposition Reaction

3. Single-Replacement Reaction

4. Double-Replacement Reaction

5. Combustion Reaction

COMBINATION (OR SYNTHESIS) REACTION

A combination reaction is where two or more

substances react to form a single new substance

Chemical example:

2Mg s + O2(g) → 2MgO(s)

+

DECOMPOSITION REACTION

A decomposition reaction is where a single

compound breaks down into two or more simpler

products (the opposite of combination reactions)

Chemical example:

2NaN3 s → 2Na s + 3N2(g)

+

SINGLE–REPLACEMENT REACTION

A single–replacement reaction is where one

element replaces a second element in a compound

Chemical example:

Zn s + Cu(NO3)2 aq → Cu s + Zn(NO3)2 (aq)

+ +

DOUBLE–REPLACEMENT REACTIONS

A double–replacement reaction involves an

exchange of positive ions between two compounds

Chemical example:

FeS s + 2HCl aq → FeCl2 s + H2S(g)

+ +

COMBUSTION

A combustion reaction is where an element or

compound (fuel) reacts with oxygen to form

carbon dioxide and water

The fuel is typically a hydrocarbon (compound

containing carbon and hydrogen)

COMPLETE AND NET IONIC EQUATIONS

Sometimes in chemical equations we are only

interested in the gases, liquids, and solids that

form

The way that we can do this is by looking at the

complete ionic equation and the net ionic

equation

COMPLETE IONIC EQUATION

The complete ionic equation shows dissolved ionic

compounds as dissociated free ions

If given the chemical equation of:

AgNO3 aq + NaCl aq → AgCl s + NaNO3(aq)

The complete ionic equation would be:

𝐴𝑔+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞 + 𝑁𝑎+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞

→ 𝐴𝑔𝐶𝑙 𝑠 + 𝑁𝑎+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞

COMPLETE IONIC EQUATION

Notice that the nitrate ion and the sodium ion

appear on both sides of the equation

We can simplifying the equation by eliminating

these ions because they do not participate in the

reaction

𝐴𝑔+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞 + 𝑁𝑎+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞

→ 𝐴𝑔𝐶𝑙 𝑠 + 𝑁𝑎+ 𝑎𝑞 + 𝑁𝑂3− 𝑎𝑞

NET IONIC EQUATION

When we simplify the equation and have only the

species undergoing the reaction, we have the net

ionic equation:

𝐴𝑔+ 𝑎𝑞 + 𝐶𝑙− 𝑎𝑞 → 𝐴𝑔𝐶𝑙 𝑠

The ions that we cancelled are the ones that are

not directly involved in the reaction. These ions

are called spectator ions

𝑁𝑂3− 𝑎𝑞 , 𝑖𝑁𝑎+ 𝑎𝑞

NET IONIC EQUATIONS

So the net ionic equation shows us what is

actually happening in the chemical reaction

ONLY single–replacement and double–

replacement reactions can be written as net ionic

equations

PREDICTING THE FORMATION OF A SOLID

During a chemical reaction if there a solid

formed, we call that solid the precipitate

This solid “precipitates” out of solution because it is

insoluble in water (cannot be dissolved)

How can we tell if we formed a solid?

We use some general rules for solubility…

SOLUBILITY RULES

(on page 372)

PREDICTING PRODUCTS

Using all of our knowledge about the 5 types of

reactions, we can predict the products of

reactions using these steps:

1. Determine what kind of reaction the reactants will

most likely form

2. Look at the solubility rules to determine if a solid

formed

3. Balance the chemical reaction

PREDICTING PRODUCTS

So if we have the following reactants:

𝐾𝐼 𝑎𝑞 , 𝑖𝑃𝑏𝑁𝑂3 𝑎𝑞

What would be the products?

Well, this is a double replacement reaction so…

𝐾𝐼 𝑎𝑞 + 𝑃𝑏𝑁𝑂3 𝑎𝑞 → 𝑃𝑏𝐼 ? + 𝐾𝑁𝑂3(? )

Did we form any solids?

YES!

𝐾𝐼 𝑎𝑞 + 𝑃𝑏𝑁𝑂3 𝑎𝑞 → 𝑃𝑏𝐼 𝑠 + 𝐾𝑁𝑂3(𝑎𝑞)