Chemical changes or chemical reactions are a main part of the study of chemistry. The first question that needs to be asked is, what is a chemical reaction? What makes these changes different from physical changes?
History
Explore the discoverer's biography, including general facts about his life and anecdotes regarding how he made this particular discovery. Also see other significant scientific discoveries built largely on this concept and other real-world applications in history that may not still be relevant.
Use/Application through History
Chemistry is a well developed but very ancient science, and chemical changes have been handled by human beings since 4,000 years ago. The Egyptians pioneered the “art” of chemistry, and since then, people have explored and continue to explore the many different aspects of chemistry. Around 1000 BCE, ancient societies discovered and mastered many chemical techniques such as how to extract metal from alloy, to make wine out of grapes or rice, to make pottery or china, and to make pigment for drawing. Throughout the rest of human history, chemistry has been used in the invention of paper, gun powder, ink, and more recently, gasoline, plastic, soap etc. Today, chemistry is used in a variey of ways across the globe.
Concept Definition
Study the primary definition of this concept, broken into general, basic, and advanced English definitions. Also see the mathematical definition and any requisite background information, such as conditions or previous definitions.
General Science
In a chemical change, the substances are altered chemically and display different physical and chemical properties after the change.
Basic
Chemical changes are often accompanied by color change, precipitation, generation of a gas, or a combination of the three.
Advanced
Substances react chemically in characteristic ways with other substances to form new substances with different characteristic properties. Chemical equations describe the overall outcomes of chemical reactions by identifying the beginning substances (reactants) and ending substances (products).
Mathematical Definition
Real World Application
Discover processes or disciplines in the natural or man-made worlds that employ the concept.
The oil industry uses chemical reactions such as cracking of petroleum.
The military uses chemical reactions in the gas bomb.
Plastic making involves chemical changes with the composition of polymers.
Turning fat or oil and alkaline solution into a bar of soap, widely used in soap industry, is a chemical change.
Reactions in the human body such as digestion, turning food into glucose, ATP, ADP formation, etc., are chemical changes.
Chemical changes even occur in art. For example the obscure oxidation drawing by Andy Warhol, was completed by using the chemical reaction of copper metallic paint oxidized by urine.
Chemical changes are everywhere!
Vocabulary
Learn important vocabulary for this concept, including words that might appear in assessments (tests, quizzes, homework, etc.) that indicate the use of this concept.
Many substances, when mixed with oxygen, will yield new products.
Videos
Browse relevant videos from the Journal of Chemical Education's (JCE) Chemistry Comes Alive! library and other video sources.
Potassium with Water
Potassium reacts vigorously with water, producing a flame in this exothermic reaction.
2K + 2H2O --> H2 + 2KOH
Cold Enough to Freeze Water
Here, the freezing of water is caused by the temperature change in a chemical reaction.
Iodine Clock
Observe color-change in a chemical reaction between two colorless solutions.
Genie in a Bottle
The classic demo: Genie in a Botttle . It demonstrates the generating of gas in some chemical changes.
Sodium Iodide and Lead(II) Nitrate
Adding very pale yellow sodium iodide to colorless lead(II) nitrate produces a yellow precipitate.
Solution A: 0.5 M sodium iodide (very pale yellow) Solution B: 0.2 M lead(II) nitrate (colorless) Precipitate: (yellow) Pb(NO3)2(aq) + 2 NaI(aq) --> PbI2(s) + 2 NaNO3(aq)
Classroom Demonstations
Investigate lab procedures suitable for live classroom demonstrations or guided student exploration.
Students requiring adaptations to gain the full benefit of a demonstration may find a worksheet with guided observations useful. Alternatively, a teacher may wish to use a worksheet with guided observations to model what observations all students should be making during a demonstration.
The Demonstration Observation Worksheet is available in
Iron will burn in the presence of oxygen if energy is added and the iron has a large surface area.
Usage:
A cool demonstration for combination reactions and the effects of surface area on reaction rates. IMPORTANT: This demonstration should not be used for labs in middle schools.
Futher Images
Credits, from left: , Yan Luo, Yan Luo, Yan Luo
Safety:
IMPORTANT: Wear gloves and goggles at all times. The instructor should stay away from the reaction and students should be kept at least 1 m away from the demonstration.
Equipment:
A 9V battery with both terminals on the same side (to complete the electric circuit)
Recommended: objects made of iron or steel
Materials:
A piece of fine steel wool (#0 or finer recommended)
Procedure:
(Recommended) For Comparison: Touch different types of iron/steel-made objects (e.g. steel ruler, clamp, ring stand) by the terminals of a 9V battery. Show the students that both terminals of the battery are in touch with the object. (No physical change can be observed).
Put a piece of fine steel wool (#0 or finer recommended, make into a loose sphere with ~1" radius) on an inflammable surface with no flammable objects near by (to prevent possible damage to surface).
Touch the steel wool with a 9V battery. (The steel wool should start burning immediately).
Notes:
What to observe: What is different when the same 9V battery is touching steel wool in Part 3 compared to other steel-made objects in Part 1? What causes the differences? Of the objects that were touched to the 9V battery, all of similar mass and made of steel, the steel wool has the largest surface area. More oxygen molecules are exposed to the steel surface in the steel wool, and therefore the energy provided by the 9V battery (which is not a lot) can only burn the steel wool but not the other objects. The chemical equation for the reaction is:
Disposal:
Used batteries should be recycled or disposed properally. The steel wool may be thrown in the garbage as long as it has stopped burning.
Difficulty:
No specific experience required
Preparation Time:
15-20 minutes
Demonstration Time:
1 minutes
Availability of Materials:
Local grocery store
Cost of materials:
$3
Last Updated:
Wed 15 Jun 2011 14:34:05 EDT
Viewed:
156017 times viewed
Source:
Rarren Fix, ScienceFix.com, June 14, 2009, ScienceFix.com
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Iodine Clock
Demonstrations
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Iodine Clock
Credit: CCAlive!
Author: Claire Liu
Description:
Most chemical changes involves color changes. The demo, "Iodine clock", is a classic color-changing reaction.
A solution of hydrogen peroxide and sulfuric acid is added to a solution of iodide ion, thiosulfate ion, and starch. A slow reaction forms triiodide, which reacts rapidly with thiosulfate, until the thiosulfate is consumed. The excess triiodide then reacts with the starch to form a blue complex.
Usage:
No Description available
Futher Images
Credits, from left: CCAlive!, CCAlive!, CCAlive!, CCAlive!
Safety:
Wear goggles and gloves.
Equipment:
Small beaker or glass bottle;
Materials:
hydrogen peroxide and sulfuric acid solution;
iodide ion, thiosulfate ion, and starch solution;
Procedure:
First put some of the solution of iodide ion, thiosulfate ion, and starch in a small beaker or glass bottle and then add the solution of hydrogen peroxide and sulfuric acid.
Notes:
No Description available
Disposal:
No Description available
Difficulty:
Some laboratory experience required
Preparation Time:
minutes
Demonstration Time:
1 minutes
Availability of Materials:
Not specified
Cost of materials:
$
Last Updated:
Tue 21 Jun 2011 12:49:01 EDT
Viewed:
67149 times viewed
Source:
University of Wisconsin press, Shakhashiri; UW-madison chemistry department; JCE CC Alive!, Shakhashiri, B.Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry
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Chemical Genie in the Bottle
Demonstrations
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Chemical Genie in the Bottle
Credit: UW-Madison Department of Chemistry
Author: Claire Liu
Description:
When a stopper is removed from an opaque bottle, an increasingly vigorous cloud of white vapor emanates from the bottle. This action results from the catalytic decomposition of 30% hydrogen peroxide by manganese dioxide.
1991, Fun With Chemistry; A Guidebook of K-12 Activities. vol 1
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Precipitation in Chemical Changes
Demonstrations
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Precipitation in Chemical Changes
Credit: CCAlive!
Author: Claire Liu
Description:
Adding very pale yellow sodium iodide to colorless lead(II) nitrate produces a yellow precipitate.
Usage:
No Description available
Futher Images
Credits, from left: CCAlive!, CCAlive!, CCAlive!, CCAlive!
Safety:
No Description available
Equipment:
No Description available
Materials:
Solution A: 0.5 M sodium iodide Solution B: 0.2 M lead(II) nitrate
Procedure:
Adding sodium iodide to colorless lead(II) nitrate.
Notes:
Solution A: 0.5 M sodium iodide (very pale yellow) Solution B: 0.2 M lead(II) nitrate (colorless) Precipitate: (yellow) Pb(NO3)2(aq) + 2 NaI(aq) --> PbI2(s) + 2 NaNO3(aq)
Disposal:
No Description available
Difficulty:
Some laboratory experience required
Preparation Time:
minutes
Demonstration Time:
1 minutes
Availability of Materials:
Not specified
Cost of materials:
$
Last Updated:
Fri 01 Apr 2011 17:05:51 EDT
Viewed:
67176 times viewed
Source:
UW-madison chemistry department; JCE CC Alive!, UW card catalog
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Summary
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Summary
The key to a chemical change is that a new substance with different chemical properties than the starting material(s) must be generated after the change. Chemical changes are most commonly indicated by changing color, the formation of a new state of matter (i.e. solid or gas in a reaction with only liquids), or flame.
Works Cited
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