2. Today’s Learning Objectives  Review Physical Properties and Physical change  Chemical Change = Chemical Reaction  Energy in a reaction  Conservations of mass

3. Example: Phase Changes Physical Change  A change in a substance that does not involve a change in the identity of the substance.

4. Other Physical Changes Reversible  Boil  Freeze  Melt  Condense Irreversible Break Split Cut Crush Physical changes can be classified as reversible or irreversible.

5. Physical Properties table What substances is a solid at -125 ° C?

6. Chemical Changes  Chemical Changes - A change in which one or more substances are converted into different substances.  During a chemical change, the composition of matter always changes.  Properties of compounds are different from their component elements. Chemical Change = Chemical Reaction

7. Chemical Reactions Chemical changes  Words that usually signify chemical change: Burn Rot Rust Possible clues to a chemical change include: transfer of energy (heat & light) change in color production of a gas formation of a precipitate - a solid that forms and settles out of a liquid mixture. Decompose Ferment Explode Corrode

8. Chemical Reactions  Chemical Properties - Relates to a substance’s ability to undergo changes that transform it into different substances Ex: iron is able to combine with oxygen to form rust, so the ability to rust is a chemical property of iron.

9. Elements & Compounds Sodium metal + Chlorine gas  Sodium Chloride Na + Cl 2  NaCl +  Shiny metal Very reactive with water Poisonous yellow gas White solid crystals, dissolves in water, flavors food

10. Types of Matter -- Elements  Atom - The smallest unit of an element that maintains the properties of that element  Element - A pure substance made of only one kind of atom

11. Types of Matter Compounds  pure substances  contains two or more elements chemically combined in a fixed proportion Examples: Table sugar (sucrose) = C 12 H 22 O 11 Water = H 2 O There are always 12 carbon, 22 hydrogen & 11 oxygen atoms in one molecule of sugar. There are always 2 hydrogen & 1 oxygen atoms in one molecule of water.

12. Elements & Compounds  A molecule is the smallest unit of an element or compound that retains all of the properties of that element or compound  Compounds can be broken down into simpler substances by chemical means (chemical change), but elements cannot.

13. Symbols of Elements  Chemists use chemical symbols to represent elements and chemical formulas to represent compounds  Symbols of Elements  First letter is always capitalized  Second letter, if there is one, is never capitalized

14. Chemical Reactions  Reactant – a substance present at the start of the reaction  Product – a substance that is produced in the reaction Fe + S  FeS Iron + Sulfur  Iron Sulfide Reactants  Products

15. C 2 H 5 OH + 3 O 2  2 CO 2 + 3 H 2 O + Energy Reactants  Products Law of Conservation of Mass  In any physical or chemical change, mass is conserved. Mass is neither created nor destroyed.  During any chemical reaction: Mass reactants = Mass products

16. Energy Changes in Chemical Reactions  Chemical Potential Energy (PE): the energy stored in chemical bonds  Heat, energy that moves from one object to another - flows from a warmer object to a cooler object

17. Reaction Pathway  Reaction Pathway: Shows the change in energy during a chemical reaction

18. Exothermic Reaction  reaction that releases energy  products have lower potential energy than reactants 2H 2(l) + O 2(l)  2H 2 O (g) + energy energy released

19. Signs of a Exothermic Reaction  Bright light  Heat  Smoke  Fire  Explosions  Temperature increases (hotter)

20. Endothermic Reaction  reaction that absorbs energy  reactants have lower potential energy than products 2Al 2 O 3 + energy  4Al + 3O 2 energy absorbed

21. Today’s Activity  Purpose : Determine is it is a physical or chemical change.

22. Today’s Activity You will be measuring the following properties of matter:  Magnetism – does it react to a magnet  Physical Property or Chemical Property????  Solubility – does it dissolve it water  Physical Property or Chemical Property???  Chemically React with Acid –  Physical Property or Chemical Property???  Gas Test – Oxygen, Carbon Dioxide OR Hydrogen Gas

23. Today’s Activity Gas Test  Hydrogen Gas  – Makes a popping noise when a match is inserted  Carbon dioxide Gas  The flame will go out  Oxygen Gas –  The flame will get bigger

24. Today’s Activity Safety Considerations  You must were goggles for the entire lab. NO EXCEPTIONS.  We are working with a strong and concentrated acid today.  If you get acid on you skin wash it quickly with soap and water  DON’T STARE at the Magnesium when you burn it.  Don’t throw matches in the trash…  Matches should go it coke cans.

25. Today’s Activity Safety Considerations  Throw acid in acid waste beaker.