physical changes, chemical changes, and how to tell the difference

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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

Introducing today’s presenter…

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Adam BoydSenior Education AssociateOffice of K–8 ScienceAmerican Chemical Society

American Chemical Society

Physical Changes, Chemical Changes, and How to Tell the Difference

Adam M. BoydEducation DivisionAmerican Chemical Society

American Chemical Society 4

Our Goals

Inquiry Based Activities

– Clues of chemical change

Science Background

– Chemical and Physical Properties

– Chemical and Physical Change

How to distinguish?


IYC Kits www.acs.org/iyckit

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


IYC Kit Lesson Components

10. Application

Student activity sheet

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IYC Kit

Classic clues of chemical change?


IYC Kit

1. Production of a gas Classic clues of chemical change?


IYC Kit

1. Production of a gas

2. Color change



IYC Kit


2. Color change

3. Formation of a precipitate



IYC Kit


2. Color change


4. Temperature change


Chemical change or Physical change?

Chemical change or Physical change?

Chemical Change Physical Change


IYC Kit


2. Color 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


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


IYC Kit


2. Color change



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Color Change

1. Teacher demo

– Carbon dioxide with a bromothymol blue indicator solution


2. Investigation

– Can you produce each color within universal indicator’s rangeby adding citric acid and sodium bicarbonate dropwise?

3. Extension: Diabetes monitoring


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.


IYC Kit


2. Color change



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Formation of a Precipitate

1. Teacher demo

– Calcium chloride + sodium carbonate


2. Investigation

– Filter precipitate formed by mixture of calcium chlorideand sodium bicarbonate

3. Extension: Water Purification


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.


IYC Kit


2. Color change



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Temperature Change

1. Teacher demo

– Foot warmer made of iron filings


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)


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.


Questions?


Our Goals

Inquiry Based Activities

– Clues of chemical change

Science Background




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


So how do we really know?

Let’s take a moment to review some chemistry fundamentals




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)


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


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)


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.


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


Chemical Change


Chemical Change

• 3 Carbon atoms

• 5 Hydrogen atoms

• 5 Oxygen atoms

• 1 Sodium atom


Chemical Change

• 3 Carbon atoms


• 5 Oxygen atoms

• 1 Sodium atom

• 3 Carbon atoms


• 5 Oxygen atoms

• 1 Sodium atom


Physical Change

• No change in chemical composition

• May suggest that a chemical change has taken place

Ice melts

H2O (s) H2O (l)


Questions?

40American Chemical Society

How to tell the difference?

In a chemical change something new is made.

Always.

41American Chemical Society

How to tell the difference?

In a physical change nothing new is made.

Always.

Popcorn II: The Quickening


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]

Thanks to today’s presenter!

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Adam BoydSenior Education AssociateOffice of K–8 ScienceAmerican Chemical Society

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physical changes, chemical changes, and how to tell the difference

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