Intro to Chemical Reactions

Chapter 6

How do you know if a chemical

reaction occurred?

We look for visual signs OR a chemical change

-If something bubbles, changes color, forms a solid (precipitate) or combusts the system has underwent a chemical change a new product exists.

Classifying reactions

In every reaction we have reactions and products

Reactants- are the chemicals present in the system

Products- are chemicals formed by the system

Types of Chemical reactions

Synthesis reactions-- 2 or more chemicals combine to form a

more complex product- A + B AB

- Examples:- The formation of potassium chloride from

potassium and chlorine gas:- 2K (s) + Cl2 (g) 2KCl

Reaction Types Cont…

Decomposition:A compound is broken down into smaller chemical species

AB A + B

Examples:

2KCl 2 K (s) + Cl2 (g)

2H2O 2H2 + O2

Reaction Types Cont…

Single Replacement (aka substitution reaction)-

One element being replaced by another element to form a compound.

A + BC AC + B

Examples:

3 Ag NO3 (aq) + Al (s) Al (NO3)3 (aq) + 3 Ag (s)

Zn + 2HCl ZnCl2 + H2

Reaction Types Cont…

Double Replacement-2 elements are being replaced to form 2 new compounds

AB + CD AD + CB

Examples:

AgNO3 + NaCl AgCl + NaNO3

SiO2 + 4HF SiF4 + 2H2O

Reaction Types Cont…

Combustion-A hydrocarbon usually reacts with oxygen to form carbon dioxide and water

Hydrocarbon + Oxygen (O2) CO2 + H2O

Examples:CH4 + 2O2 CO2 + H2O

2C2H6 + 7O2 4 CO2 + 6H2O

Practice problems:

When solid ammonium nitrite is heated, it produces nitrogen gas and water vapor

NH4NO2 N2 + 2H2O

Practice Problems

Gaseous nitrogen monoxide decomposes to produce di nitrogen monoxide gas and nitrogen dioxide gas

3NO N2O + NO2

Practice Problems

Solid mercury oxide decomposes to produce liquid mercury metal and gaseous oxygen

2HgO 2Hg + O2

Practice Problems

Solid carbon reacts with gaseous oxygen to form gaseous carbon dioxide

C + O2 CO2

Practice Problems

Solid zinc is added to an aqueous solution containing dissolved hydrogen chloride to produce gaseous hydrogen that bubbles out of the solution and zinc chloride that remains dissolved in the water

Zn + 2HCl ZnCl2 + H2