Slide 1 : Physical and Chemical Changes Change is COOL!
Physical vs. Chemical Changes : Physical vs. Chemical Changes Physical changes occur when substances or objects undergo a change without changing into another substance Chemical changes are changes substances undergo when they become new or different substances.
Physical vs. Chemical Changes : Physical vs. Chemical Changes Chemical changes happen on a molecular level http://www.chem4kids.com/files/matter_chemphys.html Physical change – object’s identity remains the same Chemical change – object’s identity changes Usually involves energy (like heat) and states of matter. Remember that after a:
Physical Change : Physical Change - Involves heat Melting of ice cream is an example of a physical change. YOUR TURN: Can you think of other examples of physical changes? Image available at http://www.icecreamclubonline.com/
Chemical Change : Chemical Change At the molecular level: The wax molecule changes to carbon dioxide and water molecules. Burning of a candle is an example of a chemical change. Image available at Colin Baird, “Chemistry in Your Life”. 2nd ed., (ISBN 0-7167-7042-3) New York: W.H. Freeman, 2006.
Slide 6 : Tarnishing of silver Corrosion (rusting) of iron Other examples of chemical changes Image available at http://www.photographersdirect.com/buyers/stockphoto.asp?imageid=1263140 Image available at http://www.mrmartinweb.com/bicycle.html
Slide 7 : Other examples of chemical changes Can you think of another term for chemical changes? YOUR TURN: Can you think of other examples of everyday life chemical reactions? Chemical change = chemical reaction
Can you identify the following changes as physical or chemical? : Can you identify the following changes as physical or chemical? Crushing a plastic bottle Melting of ice Digestion of food Formation of frost on your window Milk turns sour Fireworks
Collecting and Preserving Evidence : Collecting and Preserving Evidence Physical and chemical changes are sometimes involved in the collection of physical evidence from a crime scene Reference: M. Johll, “Investigating Chemistry: A Forensic Science Perspective.” W.H.Freeman: New York, 2007. p. 26. Ex. Latent fingerprints (invisible to the naked eye) are treated with chemicals to become visible (= chemical change) Developing latent fingerprints
Image source: http://www.clpex.com/images/Articles/RTX/s-Dsc_0025.jpg
Collecting and Preserving Evidence : Collecting and Preserving Evidence Ex. Bloody clothes are dried out to prevent the blood from decomposing. Identify the underlined words above as either a physical or chemical change. Reference: M. Johll, 2007, p. 25 Question: Why are evidence collected in separate containers?
Identifying chemical changes : Chemical changes are more difficult to identify than physical changes http://www.usoe.k12.ut.us/curr/Science/sciber00/8th/matter/sciber/chemchng.htm Identifying chemical changes smoke, and Can’t see changes in molecules But we can look for observable signs color change bubbling and fizzing light production presence of heat
Everyday life chemical changes/reactions : Everyday life chemical changes/reactions Acid-base reactions Q. Do you know where in our body do we have acids? Q. Can you give some examples of acids? Bases? Q. Can you give an example of acid-base reaction?
Everyday life chemical changes/reactions : Everyday life chemical changes/reactions Oxidation reactions Q. Can you tell which gas is used or produced during oxidation? Q. What could be an observable sign of oxidation reaction?
Slide 14 : ACID and BASESof everyday life
Slide 15 : Image available at C. Snyder, “The Extraordinary Chemistry of Ordinary Things,” 4th ed. Wiley, 2003.
Slide 16 : Image available at C. Baird and W. Gloffke, “Chemistry In Your Life.” New York: Freeman, 2003. (p. 437) Acidic soil Alkaline (basic) soil
Slide 17 : Acidic and basic are two extremes that describe chemicals, just like hot and cold are two extremes that describe temperature. Mixing acids and bases can cancel out their extreme effects; much like mixing hot and cold water can even out the water temperature. A substance that is neither acidic nor basic is neutral. http://www.epa.gov/acidrain/measure/ph.html
Slide 18 : Highly corrosive! Highly corrosive! Remember:
Low pH = high acidity Image available at http://www.phsciences.com/about_ph/ph_scale.asp