CHAPTER 11Chemical Reactions

SECTION 1Describing Chemical Reactions

SECTION 1 LEARNING TARGETS

11.1.1 – I can describe how to write a word equation.

11.1.2 – I can describe how to write a skeleton equation.

11.1.3 – I can describe the steps for writing a balanced chemical equation.

WRITING CHEMICAL EQUATIONS In a chemical reaction, one or more

reactants change into one or more products.

WORD EQUATIONS

To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.

iron + oxygen → iron (III) oxide

Iron plus oxygen yields iron (III) oxide.

Iron plus oxygen reacts to form iron (III) oxide.

CHEMICAL EQUATIONS

Chemical equation – a representation of a chemical reaction: the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

Skeleton equation – is a chemical equation that does not indicate the relative amounts of the reactants and products.

Catalyst – a substance that speeds up the reaction but is not used up in the reaction.

With out catalyst

With catalyst

Write the formulas of the reactants to the left of the yield sign (arrow) and the formulas for the products to the right.

Fe(s) + O2(g) → Fe2O3(s)

BALANCING CHEMICAL EQUATIONS Coefficients – small whole numbers that

are placed in front of the formulas in an equation in order to balance it.

Balanced equation – a chemical equation in which each side of the equation has the same number of atoms of each element and mass is conserved.

To write a balanced chemical equation, first write the skeleton equation.

Then use coefficients to balance the equation so that it obeys the law of conservation of mass.

EXAMPLES

_____ H2(g) + _____ O2(g) → _____ H2O(l)

EXAMPLES

___ AgNO3 + ___ H2S → ____ Ag2S + ___ HNO3

EXAMPLES

___ Zn(OH)2 + ___ H3PO4 → ___ Zn3(PO4)2 + ___ H2O

SECTION 2Types of Chemical Reactions

SECTION 2 LEARNING TARGETS

11.2.1 – I can describe the five general types of reactions.

11.2.2 – I can predict the products of the five general types of reactions.

CLASSIFYING REACTIONS

The five general types of reactions are combination, decomposition, single-replacement, double-replacement, and combustion.

Types of Chemical Reactions Video

COMBINATION REACTIONS

Combination reaction – chemical change in which two or more substances react to form a single new substance.

… 2Mg(s) + O2(g) → 2MgO(s)

When a Group A metal and a nonmetal react the product is an ionic compound with the metal and nonmetal.

… 2K(s) + Cl2(g) → 2KCl(s)

When two nonmetals react more than one product is possible.

… S(s) + O2(g) → SO2(g) sulfur dioxide

… 2S(s) + 3O2(g) → 2SO3(g) sulfur trioxide

Same with a transition metal and a nonmetal.

… Fe(s) + S(s) → FeS(s) iron (II) sulfide

… 2Fe(s) + 3S(s) → Fe2S3(s) iron (III) sulfide

EXAMPLE:

Write and balance the equation for the formation of magnesium nitride (Mg3N2) from its elements.

HINT: there are 7 diatomic elements: H2, N2, O2, F2, Cl2, Br2, and I2. (BrINClHOF)

DECOMPOSITION REACTIONS

Decomposition reaction – a chemical change in which a single compound breaks down into two or more simpler products.

… 2HgO(s) → 2Hg(l) + O2(g)

EXAMPLE:

Complete and balance this decomposition reaction:

HI → _____________________________________

SINGLE-REPLACEMENT REACTION Single-replacement reaction – a chemical

change in which one element replaces a second element in a compound.

Activity series – lists metals in order of decreasing activity.

Tells if one metal will replace another during a reaction.

… 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

… Br2(aq) + NaCl(aq) → no reaction

The Halogens are a reactivity series themselves:

As you go down the group the reactivity decreases so anything on top will replace anything lower in that group.

EXAMPLE:

Complete the equation for these single replacement reactions and balance each.

Fe(s) + Pb(NO3)2(aq) → ___________________

Cl2(aq) + NaI(aq) → ______________________

DOUBLE-REPLACEMENT REACTIONS Double-replacement reaction – a

chemical change involving an exchange of positive ions between two compounds.

In double-replacement reactions one or more is probably true.

1. One of the products is only slightly soluble and precipitates from solution.

Na2S(aq) + Cd(NO3)2(aq) → CdS(s) + 2NaNO3(aq)

2. One of the products is a gas.

2NaCN(aq) + H2SO4(aq) → 2HCN(g) + Na2SO4(aq)

3. One product is a molecular compound such as water.

Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + H2O(l)

EXAMPLE:

Write a balanced equation for each reaction:

NaOH(aq) + Fe(NO3)3(aq) → ______________

[iron(III)hydroxide is a precipitate]

H2SO4(aq) + Al(OH)3(aq) → ________________

COMBUSTION REACTIONS

Combustion reaction – a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light.

One reactant is always oxygen and the other is usually a hydrocarbon.

… 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l)

Complete combustion happens when the supply of oxygen is unlimited.

Incomplete combustion happens when oxygen is limited.

Other elements/compounds can react with oxygen but those reactions are usually considered to be combination reactions.

EXAMPLE:

Write a balanced equation for the complete combustion for each compound.

Formic acid (HCOOH)

Heptane (C7H16)

PREDICTING THE PRODUCTS OF A CHEMICAL REACTION The number of elements and/or

compounds reacting is a good indicator of possible reaction type and the possible products.

Aluminum with Chlorine

Elephant ToothpasteDecomposition of Peroxide

Examples

Magnesium with silver nitrate

Examples