Notes on Physical and Chemical Changes

1. Notes on Physical and Chemical Changes 09/09/11

2. Making Observations • Quantitative • Qualitative What is the difference between these terms?

3. Making Observations • Quantitative - The word quantitative means "of, relating to, or expressible in terms of quantity," according to Merriam-Webster's Dictionary. Simply put, quantitative observations are those in which the focus is the numbers. Examples are "the object is moving at 4 meters per sec", "all volumes doubled in size", or "the pressure was increased to 3 atmospheres". • Qualitative - Qualitative observations are those that provide a sense of observed parameters or changes without reference to numerical or statistical values. Qualitative observations have more to do with characteristics of what is being observed. Examples are "A heated filament glows." "The chemical turns red." "One rod is longer.“ • We used observations to identify Properties…

4. Physical Properties • Any characteristic of a material that can be observed or measured without changing the composition of the substance in the material

5. Physical Properties • Any characteristic of a material that can be observed or measured without changing the composition of the substance in the material • Examples are: viscosity, conductivity, malleability, hardness, density, and boiling/melting/freezing points.

6. Comparing Intensive vs. Extensive Properties • Intensive – Properties that do not depend on the amount of matter present.

7. Comparing Intensive vs. Extensive Properties • Intensive – Properties that do not depend on the amount of matter present. • Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density

8. Comparing Intensive vs. Extensive Properties • Intensive – Properties that do not depend on the amount of matter present. • Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density • Extensive -

9. Comparing Intensive vs. Extensive Properties • Intensive – Properties that DO NOT depend on the amount of matter present. • Examples include: Color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, density • Extensive – Properties that DO depend on the amount of matter present • Examples include: mass, weight, volume, length, width, height, amount of energy in the substance, number of moles

11. Physical Changes • A change where the substance of the material remains the same • Examples: • Braiding and unbraiding hair • Slicing an apple • Melting butter • Boiling water • Cutting hair • Ironing a shirt to remove wrinkles

12. Why is this a physical change?

13. Why is this a physical change?

14. Chemical Properties • A characteristic that produces a change in the composition of matter

15. Chemical Properties • A characteristic that produces a change in the composition of matter • Examples: flammability (the ability to burn) and reactivity (how easily a substance combines chemically with other substances)

16. Chemical Changes A change in matter that PRODUCES A NEW SUBSTANCE. In order for this to occur, a reaction has to occur. We look for evidence of a change by looking for a few “signs” that a reaction has taken place.

17. Signs of Chemical Changes • A change in color

18. Iron has reacted with oxygen

21. Signs of Chemical Changes • A change in color • The production of a gas

22. An acid reacts with an antacid

24. Signs of Chemical Changes • A change in color • The production of a gas • Formation of a precipitate (a solid formed when combining two liquids)

26. Lead iodide is the yellow solid formed and potassium nitrate is the liquid in the beaker

27. Signs of Chemical Changes • A change in color • The production of a gas • Formation of a precipitate (a solid formed when combining two liquids) • Heat is given off or absorbed

30. Signs of Chemical Changes • A change in color • The production of a gas • Formation of a precipitate (a solid formed when combining two liquids) • Heat is given off or absorbed • Light is emitted

32. Signs of Chemical Changes • A change in color • The production of a gas • Formation of a precipitate (a solid formed when combining two liquids) • Heat is given off or absorbed • Light is emitted • Change in smell or taste

33. “Smells bad”

34. “Tastes bad”