Physical Changes, Chemical Changes, and How to Tell the Difference
Transcript of Physical Changes, Chemical Changes, and How to Tell the Difference
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LIVE INTERACTIVE LEARNING @ YOUR DESKTOP
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December 5, 20126:30 p.m. – 8:00 p.m. Eastern time
Physical Changes, Chemical Changes, and How to Tell the Difference
Presented by: Adam Boyd
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Introducing today’s presenter…
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Adam BoydSenior Education AssociateOffice of K–8 ScienceAmerican Chemical Society
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American Chemical Society
Physical Changes, Chemical Changes, and How to Tell the Difference
Adam M. BoydEducation DivisionAmerican Chemical Society
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Our Goals
Inquiry Based Activities
– Clues of chemical change
Science Background
– Chemical and Physical Properties
– Chemical and Physical Change
How to distinguish?
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IYC Kits www.acs.org/iyckit
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1. Lesson Summary
2. Key Concepts
3. Safety
4. The chemistry continues
5. Scientist introduction
6. Teacher demonstration(s)
7. Student activity
8. Class discussion
9. Teacher demonstration
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IYC Kit Lesson Components
10. Application
Student activity sheet
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IYC Kit
Classic clues of chemical change?
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IYC Kit
1. Production of a gas Classic clues of chemical change?
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IYC Kit
1. Production of a gas
2. Color change
Classic clues of chemical change?
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
Classic clues of chemical change?
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
4. Temperature change
Classic clues of chemical change?
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Chemical change or Physical change?
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Chemical change or Physical change?
Chemical Change Physical Change
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
4. Temperature change
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Production of a Gas
1. Teacher demo
– Citric acid + sodium bicarbonate
– Ask students: was this a chemical change?
2. Investigation
– “Foam dome”
– Mix citric acid solution with sodium bicarbonate and liquid detergent
– Controlling products of a chemical reaction
3. Extension: Air Bags
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Production of a Gas
1. The production of a gas is one clue that a chemical change may have taken place
2. You can control the amount of products formed by controlling the amount of reactants
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
4. Temperature change
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Color Change
1. Teacher demo
– Carbon dioxide with a bromothymol blue indicator solution
– Ask students: was this a chemical change?
2. Investigation
– Can you produce each color within universal indicator’s rangeby adding citric acid and sodium bicarbonate dropwise?
3. Extension: Diabetes monitoring
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Color Change
1. A color change is one clue that a chemical change may have taken place
2. Adding a base to an acidic solution makes the solution less acidic.
3. Adding an acid to a basic solution makes the solution less basic.
4. Carbon dioxide gas reacts with water to form carbonic acid.
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
4. Temperature change
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Formation of a Precipitate
1. Teacher demo
– Calcium chloride + sodium carbonate
– Ask students: was this a chemical change?
2. Investigation
– Filter precipitate formed by mixture of calcium chlorideand sodium bicarbonate
3. Extension: Water Purification
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Formation of a Precipitate
1. The formation of a precipitate is one clue that a chemical change may have taken place
2. A precipitate is a solid that forms in the chemical reaction between liquids. It does not dissolve in the resulting solution.
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IYC Kit
1. Production of a gas
2. Color change
3. Formation of a precipitate
4. Temperature change
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Temperature Change
1. Teacher demo
– Foot warmer made of iron filings
– Ask students: was this a chemical change?
2. Student Activity
– Citric acid + sodium bicarbonate (Endothermic)
– Sodium bicarbonate + calcium chloride (Exothermic)
3. Investigation
– Adjust reactants to get temperature between 40° and 50° C.
4. Extension: Meals-Ready-to-Eat (MREs)
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Temperature Change
1. A temperature change is one clue that a chemical change may have taken place
2. When the temperature increases during a chemical reaction, it is called an exothermic reaction.
3. When the temperature decreases during a chemical reaction, it is called an endothermic reaction.
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Questions?
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Our Goals
Inquiry Based Activities
– Clues of chemical change
Science Background
– Chemical and Physical Properties
– Chemical and Physical Change
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Toss Up: Chemical or Physical?
• Adding Kool-Aid mix to water
• Smoke emanates from dry ice at room temperature
• Mentos are dropped into a 2-liter of Diet Coke
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So how do we really know?
Let’s take a moment to review some chemistry fundamentals
– Chemical and Physical Properties
– Chemical and Physical Change
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Chemical Properties
• Exhibited by matter as it undergoes changes in composition
• Related to the kinds of chemical changes that substances undergo
Examples – Photosynthesis
• In the presence of sunlight and chlorophyll, carbon dioxide reacts with water to produce glucose and oxygen
– Metal Rusts• Iron reacts with oxygen and water to produce iron oxides and iron hydroxides (rust)
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Physical Properties
• Can be observed in the absence of any change in composition
• Some depend on conditions under which they are measured
Examples: color, density, hardness, melting point, boiling point
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Chemical Change
1. One or more substances are used up (at least partially)
2. One or more new substances are formed
Examples
Photosynthesis
6CO2 + 6H2O C6H12O6 + 6O2
Metal Rusts
2Fe(s) + 3/2 O2(aq) + xH2O(l) Fe2O3 · xH2O(s)
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Chemical Change
• The reactants are on the left side of the equation and the products are on the right.
• In the reaction, the bonds in the methane and oxygen come apart, the atoms rearrange and then re-bond to form water and carbon dioxide.
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Chemical Change
• All the atoms in the reactants form the products so the mass of the reactants and the products is the same.
• No new atoms are created and no atoms are destroyed
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Chemical Change
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Chemical Change
• 3 Carbon atoms
• 5 Hydrogen atoms
• 5 Oxygen atoms
• 1 Sodium atom
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Chemical Change
• 3 Carbon atoms
• 5 Hydrogen atoms
• 5 Oxygen atoms
• 1 Sodium atom
• 3 Carbon atoms
• 5 Hydrogen atoms
• 5 Oxygen atoms
• 1 Sodium atom
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Physical Change
• No change in chemical composition
• May suggest that a chemical change has taken place
Ice melts
H2O (s) H2O (l)
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Questions?
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How to tell the difference?
In a chemical change something new is made.
Always.
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How to tell the difference?
In a physical change nothing new is made.
Always.
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Popcorn II: The Quickening
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A few closing notes
• IYC kit makes clear definition of chemical change immediately• Remember to complete the evaluation to receive a free IYC kit
• For more free resources:middleschoolchemistry.cominquiryinaction.orgacs.org/iyckit
• Contact UsAdam Boyd | [email protected] Kessler | [email protected]
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Thanks to today’s presenter!
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Adam BoydSenior Education AssociateOffice of K–8 ScienceAmerican Chemical Society
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