Chemical Reactions

Reactions and EquationsChapter 10, Section 1

Evidence of Chemical Reactions

Chemical Reaction: the process by which the atoms of one or more substances are rearranged to form different substances Break down food to produce energy Produce natural fibers, cotton and

wool

Representing Chemical Reactions

Reactants: the starting substances Products: the substances formed

during the reaction

reactant 1 + reactant 2 product 1 + product 2 Reactants written to

the left of the arrow Arrow is read as “react to produce” or “yields”.

Products are written to the right of the arrow

Symbols Used in Equations

Symbol

Meaning

+ Separates 2 or more reactants or products

Separates reactants from products

(s) Identifies a solid state

(l) Identifies a liquid state

(g) Identifies a gaseous state

(aq) Identifies water solution

Example

How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide?

Example

How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide?

First write the chemical formulas for the reactants to the left of the arrow including their physical states.

C(s) + S(s)

Example

How would you write the equation that describes the reactions between carbon and sulfur to form carbon disulfide?

Finally write the chemical formula for the product, liquid carbon disulfide to the right of the arrow, indicating its physical state.

C(s) + S(s) CS2(l)

Practice Problems

Write skeleton equations for the following word equations.

Hydrogen(g) + bromine(g) hydrogen bromide(g)

Carbon monoxide(g) + oxygen(g) carbon dioxide(g)

Potassium chlorate(s) potassium chloride(s) + oxygen(g)

Balancing Chemical Equations Chemical Equation: a statement that uses

chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

Steps for Balancing Equations1. Write the skeleton equation for the reaction.

ex. H2(g) + Cl2(g) HCl(g)

2. Count the atoms of the elements in the reactants.ex. H2 2 atoms of H

Cl2 2 atoms of Cl3. Count the atoms of the elements in the products.

ex. HCl 1 atom H + 1 atom Cl4. Change the coefficients to make the number of atoms

of each element equal on both sides of the equation. Never change a subscript!!ex. H2(g) + Cl2(g) 2HCl(g)

Steps for Balancing Equations5. Write the coefficient in their lowest possible ratio.

ex. (2:2) (1:1)6. Check your work.

Example Problem

Write the balanced chemical equation for the reaction in which sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. The reaction occurs in water.

Example Problem

Write the balanced chemical equation for the reaction in which sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. The reaction occurs in water.

2NaOH(aq) + CaBr2(aq) Ca(OH)2(s) + 2NaBr(aq)

Practice Problems Write chemical equations for each of the

following reactions. In water, iron(III) chloride reacts with sodium

hydroxide, producing solid Iron (III) hydroxide and sodium chloride.

Liquid carbon disulfide reacts with oxygen gas, producing caron dioxide gas and sulfur dioxide gas.

Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfide.

Chemical Reactions

Classifying Chemical Reactions

Chapter 10, Section 2

Types of Chemical Reactions

Synthesis Combustion Decomposition Single-replacement Double-replacement

Synthesis Reactions

A chemical reaction in which two or more substances react to produce a single product. A + B AB

Ex. 2Na + Cl2 2NaCl Ex. CaO + H2O Ca(OH)2

Ex. 2SO2 + O2 2SO3

Combustion Reactions

A reaction during which oxygen combines with a substance and releases energy in the form of heat and light. Ex. 2H2 + O2 2H2O Ex. C + O2 CO2

Ex. CH4 + 2O2 CO2 + 2H2O

Practice Problems Write chemical equations for the

following reactions. Classify each reaction into as many categories as possible. The solids aluminum and sulfur react to

produce aluminum sulfide Water and dinitrogen pentoxide gas react

to produce aqueous hydrogen nitrate. The gases nitrogen dioxide and oxygen

react to produce dinitrogen pentoxide gas. Ethane gas (C2H6) burns in air, producing

carbon dioxide gas and water vapor.

Decomposition Reactions

A reaction in which a single compound breaks down into two or more elements or new compounds Ex. AB A + B

Ex. NH4NO3 N2O + 2H2O Ex. 2NaN3 2Na + 3N2

Practice Problems Write chemical equations for the

following decomposition reactions. Aluminum oxide decomposes when

electricity is passed through it. Nickel (II) hydroxide decomposes to

produce nickel (II) oxide and water. Heating sodium hydrogen carbonate

produces sodium carbonate, carbon dioxide and water.

Replacement Reactions – Single & Double

Single-replacement reaction: A reaction in which the atoms of one element replace the atoms of another element in a compound. Ex. A + BX AX + B

Ex. Cu + 2AgNO3 2Ag + Cu(NO3)2

Replacement Reactions

** A metal will not always replace another metal

Reactivity determines whether or not a metal will replace another metal.

The most active metals, do not replace metals

Example Problem

Predict the products that will result when these reactants combine and write a balanced chemical equation for each reaction. Fe + CuSO4

Br2 + MgCl2 Mg + AlCl3

Practice Problems

Predict if the following single-replacement reactions will occur. If a reaction occurs, write a balanced equation for the reaction. 2K + ZnCl2 Cl2 + 2HF Fe + Na3PO4

Double Replacement Reactions

A reaction involving the exchange of positive ions between two compounds dissolved in water most often producing a precipitate, water or a gas (H2S, HCN, and CO2) Ex. AX + BY AY + BX

Ex. Ca(OH)2 + 2HCl CaCl2 + 2H2O Ex. 2NaOH + CuCl2 2NaCl + Cu(OH)2

Guidelines for Double-Replacement Reactions

Step Example

1. Write the components of the reactants in a skeleton equation.

Al(NO3)3 + H2SO4

2. Identify the cations and anions in each compound.

Al(NO3)3 has Al3+ and NO3-

H2SO4 has H+ and SO42-

3. Pair up each cation with the anion from the other compound.

Al3+ pairs with SO42-

H+ pairs with NO3-

4. Write the formulas for the products using the pairs from step 3

Al2(SO4)3

HNO3

5. Write the complete equation for the double-replacement reaction.

Al(NO3)3 + H2SO4 Al2(SO4)3 + HNO3

6. Balance the equation. 2Al(NO3)3 + 3H2SO4 Al2(SO4)3 + 6HNO3

Practice Problems Write the balanced chemical equations

for the following double-replacement reactions. Aqueous lithium iodide and aqueous silver

nitrate react to produce solid silver iodide and aqueous lithium nitrate.

Aqueous barium chloride and aqueous potassium carbonate react to produce solid barium carbonate and aqueous potassium chloride.

Aqueous sodium oxalate and aqueous lead(II) nitrate react to produce solid lead(II) oxalate and aqueous sodium nitrate.

Predicting Products of Chemical Reactions

Class of Reaction Reactants Probable Products

Synthesis Two or more substances One compound

Combustion A metal and oxygenA nonmetal and oxygenA compound and oxygen

The oxide of the metalThe oxide of the nonmetalTwo or more oxides

Decomposition One compound Two or more elements and/or compounds

Single-replacement

A metal and a compoundA nonmetal and a compound

A new compound and the replaced metal. A new compound and the replaced nonmetal.

Double-replacement

Two compounds dissolved in water

Two different compound, one of which is often a solid, water or a gas.

Chemical Reactions

Reactions in Aqueous Solutions

Chapter 10, Section 3

Aqueous Solutions

Solutes: a substance dissolved in a solution

Solvent: the substance that dissolves a solute to form a solution

Aqueous solution: a solution in which the solvent is water

Reactions that Form Precipitates

2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)

In solution, these exist as ions. When their solutions are mixed, a precipitate of

copper (II) hydroxide forms.Ionic equations are written to show the

details of the reaction. 2Na+

(aq) + 2OH-(aq) + Cu2+

(aq) + 2Cl-(aq) 2Na+

(aq) + 2Cl-(aq) + Cu(OH)2(s)

Reactions that From Precipitates Complete ionic equation: an ionic

equation that shows all of the particles in a solution as they realistically exist

Spectator ions: ions that do not participate in a reaction

Net ionic equations: ionic equations that include only the particles that participate in the reaction

Example Problem

Write the chemical, complete ionic and net ionic equation for the reaction between aqueous solutions of barium nitrate and sodium carbonate that forms the precipitate barium carbonate.

Practice Problems Write chemical, complete ionic and net ionic equations

for the following reactions that may produce precipitates. Use NR to indicate that no reaction occurs.

Aqueous solutions of potassium iodide and silver nitrate are mixed, forming the precipitate silver iodide.

Aqueous solutions of ammonium phosphate and sodium sulfate are mixed. No precipitate forms and no gas is produced.

Aqueous solutions of aluminum chloride and sodium hydroxide are mixed, forming the precipitate aluminum hydroxide.

Aqueous solutions of lithium sulfate and calcium nitrate are mixed, forming the precipitate calcium sulfate.

Aqueous solutions of sodium carbonate and manganese (V) chloride are mixed, forming the precipitate manganese (V) carbonate.

Reactions That Form Water Double replacement reaction No evidence of chemical reaction is

observable

HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq)

Complete Ionic Equation:H+

(aq) + Br-(aq) + Na+

(aq) + OH-(aq) H2O(l) + Na+

(aq) + Br-

(aq)

Reactions That Form Water

Crossing out the spectator ions leaves us with:

H+(aq) + OH-

(aq) H2O(l)

(net ionic equation)

Example Problem

Write the chemical, complete ionic and net ionic equations for the reaction between hydrochloric acid and aqueous lithium hydroxide, which produces water.

Practice Problems Write chemical, complete ions and net ionic

equations for the reactions between the following substances, which produce water. Sulfuric acid and aqueous potassium hydroxide Hydrochloric acid and aqueous calcium hydroxide Nitric acid and aqueous ammonium hydroxide Hydrosulfuric acid and aqueous calcium hydroxide Phosphoric acid and aqueous magnesium hydroxide

Reactions that Form Gases Double Replacement Reaction Commonly produce CO2, H2S and HCN

2HI(aq) + Li2S(aq) H2S(g) + 2LiI(aq)

Ionic Equation2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq)

H2S(g) + 2Li+(aq) + 2I-(aq)

Example Problem

Write the chemical, complete ionic and net ionic equations for the reaction between hydrochloric acid and aqueous sodium sulfide which produces hydrogen sulfide gas.

Practice Problems Write chemical, complete ionic and net

ionic equations for these reactions. Perchloric acid reacts with aqueous

potassium carbonate Sulfuric acid reacts with aqueous sodium

cyanide Hydrobromic acid reacts with aqueous

ammonium carbonate Nitric acid reacts with aqueous potassium

rubidium sulfide