Atoms and Molecules
- History of the Atom
- Models for the Atom
- Subatomic Particles
- Periodic Table
- Periodic Trends
- Polyatomic Ions
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|Reactions - Physical and Chemical Changes|
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?
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.
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.
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.
In a chemical change, the substances are altered chemically and display different physical and chemical properties after the change.
Chemical changes are often accompanied by color change, precipitation, generation of a gas, or a combination of the three.
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).
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!
Learn important vocabulary for this concept, including words that might appear in assessments (tests, quizzes, homework, etc.) that indicate the use of this concept.
|balanced chemical equation||
Browse relevant videos from the Journal of Chemical Education's (JCE) Chemistry Comes Alive! library and other video sources.
Potassium reacts vigorously with water, producing a flame in this exothermic reaction.
2K + 2H2O --> H2 + 2KOH
Here, the freezing of water is caused by the temperature change in a chemical reaction.
Observe color-change in a chemical reaction between two colorless solutions.
The classic demo: Genie in a Botttle . It demonstrates the generating of gas in some chemical changes.
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)
Pb(NO3)2(aq) + 2 NaI(aq) --> PbI2(s) + 2 NaNO3(aq)
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
Chemical Genie in the Bottle
Precipitation in Chemical Changes
Read a summary of the concept, indicating the enduring understanding students should retain after class.
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.
Review the works cited to write the researched parts of this page, such as the discover's biographical information and other areas.
The picture in "Application Throughout History":
The picture in classroom demostrations:
The picture of oxidation painting done by Andy Warhol