Chemical Reactions

Evidence of Chemical Reactions

Temperature change Release of energy (heat or light) Color Change Odor Gas Bubbles

Representing Chemical Reactions

All chemical reactions have two parts: Reactants and Products.

Reactants Products

Example:aluminum(s) + bromine(l) aluminum

bromide(s)

Example:aluminum(s) + bromine(l) aluminum

bromide(s)

Skeleton equation:

Al (s) + Br2 (l) AlBr3 (s)

Write the skeleton equation for the following word equations Hydrogen and bromine gases react to

yield hydrogen bromide. hydrogen (g) + bromine (g) hydrogen

bromide (g) H2 (g) + Br2 (g) HBr (g)

Carbon monoxide and oxygen react to form carbon dioxide. carbon monoxide (g) + oxygen (g) carbon

dioxide (g) CO (g) + O2 (g) CO2 (g)

Writing Chemical Equations

Step 1: Write a skeleton equation from a word equation Hydrogen (g) + Chlorine (g) H2 (g) + Cl2 (g) HCl (g)

Step 2: Count all of the atoms in the reactants H2 (g) + Cl2 (g) HCl (g)

2 2 Step 3: Count number of atoms in products

H2 (g) + Cl2 (g) HCl (g)

2 atoms total

Step 4: Change the coefficients to make the number of atoms of each element equal on both sides of the equation. H2 (g) + Cl2 (g) 2HCl

2 2 4

Example Problem

Write a balanced chemical equation for the reaction in which aqueous sodium hydroxide and aqueous calcium bromide produce solid calcium hydroxide and aqueous sodium bromide.

NaOH(aq) + CaBr2(aq) Ca(OH)2(s) + NaBr(aq) How many atoms in the reactants?

5 How many atoms in the products?

7 Balanced equation:

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

Diet Coke and Mentos “Reaction”

Four Types of Chemical Reactions

Synthesis Combustion Decomposition Replacement (Single-Replacement,

Double-Replacement)

Synthesis Reactions

Two reactants form one product A + B AB

It can either be two elements or two compounds reacting to form a new compound.

Example: CaO(s) + H2O(l) Ca(OH)2

An element and a compound can also combine Example: SO2(g) + O2(g) SO3(g) 2SO2(g) + O2(g) 2SO3(g)

Decomposition Reactions

This is when a compound breaks down into two or more elements or other compounds AB A + B

Example: NaN3(s) Na(s) + N2(g) Balanced? 2NaN3(s) 2Na(s) + 6N2(g)

Single-Replacement Reaction

A compound reacts with an element and one element replaces one of the atoms.

A + BX AX + B Example:

Li(s) + H2O(l) LiOH(aq) + H2(g) 2Li(s) + 2H2O(l) 2LiOH + H2(g)

Double Replacement

AX + BY AY + BX Example:

Ca(OH)2(aq) + HCl(aq) CaCl2(aq) + H2O (l) Balanced? Ca(OH)2(aq) + 2HCl(aq) CaCl2(aq) + 2H2O (l)

Combustion Reactions

In combustion reactions Oxygen combines with a substance and releases energy in the form of heat and light. (FIRE)

A common example of this is burning coal C(s) + O2 (g) CO2

Another common example is the combustion of hydrogen to make water. H2(g) + O2(g) H2O (g) 2H2(g) + O2(g) 2H2O(g)

Reactions in Aqueous Solution

An aqueous solution contains one or more dissolved substances called solutes.

In an aqueous solution the solvent is water.

In an aqueous solution of Hydrocholric acid…

HCl(aq) H+(aq) + Cl-(aq)

In an aqueous solution of sodium hydroxide

NaOH(aq) Na+(aq) + OH-(aq)

1. All salts of Group IA, and ammonium are soluble.  2. All salts of nitrates, chlorates and acetates are

soluble. 3. All salts of halides are soluble except those of

silver(I),  copper(I), lead(II), and mercury(I).  4. All salts of sulfate are soluble except for barium

sulfate, lead(II) sulfate, and strontium sulfate.  5. All salts of carbonate, phosphate and sulfite are

insoluble, except for those of group IA and ammonium. 

6. All oxides and hydroxides are insoluble except for those of group IA, calcium, strontium and  barium. 

7. All salts of sulfides and insoluble except for those of Group IA and IIA elements and of ammonium.

Solubility Rules

Reactions that form Precipitates

Some reactions that occur in aqueous solution produce solid precipitates.

For example… 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) +

Cu(OH)2(s) An ionic equation shows in detail the ions

that exist in the solution…

Practice

Write the ionic equations and the net ionic equation for the reactions…

Ba(NO3)2(aq) + Na2CO3(aq) BaCO3(s) + NaNO3(aq)

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

Reactions that form water

Acid-Base neutralizations are usually double replacement reactions that result in the formation of water.

In general an acid is a compound that, when dissolved in water produces H+ ions.

Examples – HCl, HBr, H2SO4

In general a base is a compound that, when dissolved in water produces OH- ions.

Examples: NaOH

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

Complete ionic equation: H+(aq) + Br-(aq) + Na+(aq) + OH-(aq)

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

Net ionic equation: H+(aq) + OH-(aq) H2O(l)

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

Test Review

Aqueous barium chloride and aqueous sodium fluoride are mixed.

Aqueous copper (I) nitrate and aqueous potassium sulfide are mixed

Aqueous sodium hydroxide and aqueous copper (II) chloride are mixed.

Aqueous sodium carbonate and aqueous calcium nitrate are mixed.

Aqueous sodium sulfate and aqueous potassium carbonate are mixed.