1. Chapter 7.1 Notes Describing Reaction

2. Physical VS Chemical Properties a.Physical vs Chemical Properties a.Physical Change – A change that occurs when some of the properties of a material change, but the substances in the material remain the same. b.Chemical Change – A change that occurs when a substance reacts and forms on or more new substances.

3. Physical VS Chemical Properties i.Signs of a chemical change include color change, temperature change, light produced, gas formed, precipitate formed. c.When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.

4. Chemical Reactions a.Chemical Reactions a.A useful description of a chemical reaction tells you the substances present before and after the reaction. b.Reactants – The substances that undergo change and are present before the reaction takes place.

5. Chemical Reactions c.Products – The new substances formed as a result of that change and are present after the reaction takes place. d.A chemical equation is a representation of a chemical reaction in which the reactants and products are expressed as formulas. e.Reactants  Products

6. Example 1: Burning Charcoal Word Equation: Carbon + Oxygen = Carbon Dioxide Chemical Formula: C + O 2 = CO 2

7. Conservation of Mass c.Conservation of Mass a.The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. b.Therefore the mass of the products is always equal to the mass of the reactants.

8. Conservation of Mass c.While burning charcoal you actually see the charcoal burn and disappear. The same mass of charcoal that appears to have disappeared is actually converted into carbon dioxide gas.

9. Balancing Equations d.Balancing Equations a.In order to show that mass is conserved during a reaction, a chemical equation must be balanced. b.Chemical equations can be balanced by changing the coefficients (the numbers that appear before symbols.) c.When balancing a chemical equations never change the subscripts in the formula.

10. E. Steps to Balancing a Chemical Formula e.Steps to Balancing a Chemical Formula a.Step 1: Count the number of atoms of each element on each side of the equation. b.Step 2: change one or more coefficients until the equation is balanced. (Only change the coefficients that need to be changed.)

11. Ex. 1) Write a balanced equation for the reaction between copper and oxygen to produce copper(II) and oxide, CuO. What do you Know? - Reactants: Cu, O2 - Product: CuO What do you need to know? - Balanced Equation Plan and Solve: - Write a chemical equation with the reactants on the left side and the product on the right side - Cu + O 2  CuO - Change the coefficient of CuO in order to balance the number of O atoms. - Cu + O 2  2CuO - Change the coefficient of Cu. - 2Cu + O 2  2CuO Answer:

12. Ex. 2) Balance the equation H 2 O 2  H 2 O + O 2 What do you Know? - Reactants: H2O2 - Product: H 2 O + O 2 What do you need to know? - Balanced Equation Plan and Solve: - Write a chemical equation with the reactants on the left side and the product on the right side - H 2 O 2  H 2 O + O 2 - Change the coefficient of H 2 O 2 and H2O in order to balance the number of H and O atoms. - 2H 2 O 2  2H 2 O + O 2 Answer:

13. Ex. 3) Balance the equation Mg + HCl  H 2 + MgCl 2 What do you Know? - Reactants: Mg, HCl - Product: H 2, MgCl 2 What do you need to know? - Balanced Equation Plan and Solve: - Write a chemical equation with the reactants on the left side and the product on the right side - Mg + HCl  H 2 + MgCl 2 - Change the coefficient of HCl in order to balance the number of H and Cl atoms. - Mg + 2HCl  H 2 + MgCl 2 Answer:

14. Counting With Moles f.Counting With Moles a.A mole is an amount of a substance that contains approximately 6.02 X 10 23 particles of that substance. This number is known as Avogadro’s number b.Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of a substance.

15. Molar Mass g.Molar Mass a.Molar mass is the mass of one mole of a substance. b.In the same way that a dozen eggs has a different mass than a dozen oranges, a mole of carbon would have a different mass than a mole of sulfur. c.The molar mass is the same as the atomic mass expressed in grams

16. Molar Mass d.For a compound you can calculate the molar mass by adding up the atomic masses of its component atoms, and then expressing the sum in grams. Ex. 4) Find the molar mass of a molecule of CO 2. One carbon= 12amu Two Oxygen= 16amu x 2 = 32amu 12amu+32amu = 44.0 grams.

17. Mole-Mass Conversion h.Mole – Mass Conversion a.Once you know the molar mass of a substance, you can convert moles of that substance into mass, or a mass of that substance into moles.

18. Ex. 5) Convert 55.0 g of CO 2 to moles. What do you know? 44.0 g CO 2 = 1 mol CO 2 What do you want to know? 55.0g CO 2 in moles Plan and Solve: Use a conversion factor. 55.0g CO 2 X (1mol CO 2 /44.0g CO 2 ) Answer: = 1.25mol CO 2

19. Ex. 6 Convert 144g of H 2 O to moles What do you know? 18g of H 2 O = 1 mol of H 2 O What do you want to know? How many moles is 144g of H 2 O? Plan and Solve: Use a conversion factor. 144g H 2 O X (1mol H 2 O/18g H 2 O) Answer: 144g H 2 O = 8.00 mol H 2 O