2. CHEMICAL REACTIONS & EQUATIONS

3. But First a Quick Review…

4. Elements n Elements are pure substances u made of only one kind of material u has definite properties u is the same all throughout n They cannot be broken down into simpler substances without losing their identity n Represented by a symbol (Au,Na) n They’re on the periodic table!

5. Compounds n Made up of 2 or more different elements that are chemically combined. n They are represented by formulas n Ex: H 2 O, NaCl, C 6 H 12 O 6, CO 2 n Compounds have different properties than their original elements n They cannot be separated by physical means n Unlike elements, compounds can only be broken down to simpler substances through a chemical reaction

6. Compounds n The properties of the elements that make up a compound are often quite different from the properties of the compound itself u Sodium – Na = highly reactive metal u Chlorine – Cl = poisonous gas Sodium Chloride = NaCl (table salt)

7. Mixtures n Mixtures - two or more substances that are physically combined and retain the properties of their substances u Mixture of elements – brass (mixture of copper and zinc) u Mixture of elements and compounds – air u Mixture of compounds – sand, saltwater u Solution – particles are evenly distributed

8. Types of Mixtures n Homogeneous - Entire mixture looks the same throughout u Ex. Milk, Bronze n Heterogeneous – Parts of the mixture look different u Ex. Fruit Salad, Trail Mix Both types of mixtures can be separated by a physical change!

9. Element, Compound, or Mixture ? ? ?

10. Quick Check Element, Compound, or Mixture? 1. Platinum 2. Carbon Dioxide 3. Air 4. Brass 5. Glucose Element Compound Mixture Compound Pt CO 2 C 6 H 12 O 6 Alloy of Cu and Zn O 2, N 2, and Ar

11. Molecules n A molecule is 2 or more atoms chemically bonded n Water-2 atoms of hydrogen and one atom of oxygen-together they form one molecule of H 2 O n All compounds are molecules but not all molecules are compounds u H 2 is a molecule, but not a compound u H 2 O is both a molecule and a compound (notice the 2 different elements)

12. Quick Check Which substances are molecules and which substances are both molecules and compounds? 1. O 2 2. CO 2 3. C 6 H 12 O 6 4. Cl 2 5. NH 3 Molecule Both Molecule Both

13. Chemical Formulas n Chemcial Formulas - a shorthand way of representing compounds u If chemical symbols are the “letters,” these are the “words.” F Ex: NH 3 = ammonia, C 3 H 7 OH = rubbing alcohol n Sometimes, the formula represents a molecule of a single element. u These are called diatomic molecules. This is how that element is naturally found. F O 2 -Oxygen H 2 -Hydrogen Cl 2 -Chlorine

14. Let’s Break it Down CO 2 = Carbon Dioxide H 2 0 = Water C 6 H 12 O 6 = Glucose O 2 = Oxygen Formula for Photosynthesis: 6CO 2 + 6H 2 0 + energy from sunlight C 6 H 12 O 6 + 6O 2

15. Chemical Equations A chemical equation is a symbolic representation of a chemical reaction 22

16. Equation Example: The burning of methane gas in oxygen is: CH 4 + 2 O 2 → CO 2 + 2 H 2 O

17. Chemical Formulas - Subscripts n Subscripts are small numbers used in chemical formulas n Shows the elements & number of atoms of each element in a molecule n H 2 SO 4 u Elements F Hydrogen; 2 atoms F Sulfur: 1 atom F Oxygen: 4 atoms u 7 atoms total subscript

18. Coefficients n A formula may begin with a number n If there is no number, then “1” is understood to be in front of the formula. u This number is called the coefficient u The coefficient represents the number of molecules of that compound or atom needed in the reaction u For example: F 2H 2 SO 4 – 2 molecules of Sulfuric Acid Coefficient

19. Coefficients n 2H 2 SO 4 – 2 molecules of Sulfuric Acid u A coefficient is distributed to ALL elements in a compound F 2 H 2 (for a total of 4 H atoms) F 2S (for a total of 2 S atoms) F 2O 4 (for a total of 8 O atoms)

20. Reading Chemical Equations n Each side of an equation represents a combination of chemicals n The combination is written as a set of chemical formulas, separated by + symbols. CH 4 + 2 O 2 → CO 2 + 2 H 2 O Coefficient

21. The equation for the burning of methane gas in oxygen is: CH 4 + 2 O 2 → CO 2 + 2 H 2 O Subscript Shows # of atoms Coefficient Shows # of molecules

22. Reading Chemical Equations n The two sides of the equation are separated by an arrow u The combination of chemicals before the reaction are on the left side of the arrow u The right side indicates the combination of chemicals after the reaction

23. Language of Chemical Equations n In this reaction, sodium (Na) and oxygen (O 2 ) react to produce a single molecule, Na 2 O 4Na + O 2 → 2Na 2 O Reactants Products Yields n Reactants n Arrow (yields) n Products

24. Na NaO Yields Reactants Products SubscriptCoefficient Language of Chemical Equations