Chemical Reactions

1. Chemical Reactions Theme: Changes and Reactions

2. Physical Properties (Review) • color • melting point • boiling point • electrical conductivity • specific heat • density • state (solid, liquid, or gas) LecturePLUS Timberlake

3. Physical Change (Review) Changes in physical properties • melting • boiling • condensation No change occurs in the identity of the substance Example: Ice , rain, and steam are all water LecturePLUS Timberlake

4. Chemical Change • Atoms in the reactants are rearranged to form one or more different substances • Old bonds are broken; new bonds form Examples: Fe and O2 form rust (Fe2O3) Ag and S form tarnish (Ag2S) LecturePLUS Timberlake

5. Learning Check 1 Classify each of the following as a 1) physical change or 2) chemical change A. ____ a burning candle B. ____ melting ice C. ____ toasting a marshmallow D. ____ cutting a pizza E. ____ polishing silver LecturePLUS Timberlake

6. Solution 1 Classify each of the following as a 1) physical change or 2) chemical change A. __2__ a burning candle B. __1_ melting ice C. __2__ toasting a marshmallow D. __1__ cutting a pizza E. __2__ polishing silver LecturePLUS Timberlake

7. Main Ideas • Chemical Reactions are represented by Chemical Equations.

8. Main Ideas • Chemical Equations are balanced to show the same number of atoms of each element on each side. • The Law of Conservation of Matter (Mass) says that atoms won’t be created or destroyed in a chemical reaction. That is why chemical equations must be balanced!

9. Chemical Reactions are Everywhere Cooking Respiration

10. Chemical Reactions are Everywhere Hair Dye Auto Fuel

11. Vocab • Reactants • Products • Chemical Formula • Chemical Equation • Coefficients

12. Chemical Reaction A process in which at least one new substance is produced as a result of chemical change. LecturePLUS Timberlake

13. Chemical Equations • Reactants produce Products • Reactants Products

14. A Chemical Reaction Reactants Products LecturePLUS Timberlake

15. Learning Check 2 A. How does an equation indicate a change in the identity of the reacting substances? B. How did the yellow and green reactants combine? C. Did all the reactants form product? Why or why not? LecturePLUS Timberlake

16. Solution 2 A. How does an equation indicate a change in the identity of the reacting substances? The formulas of the reactants are different than the formulas of the products. B. How did the yellow and green reactants combine? 1 yellow combined with 1 green. C. Did all the reactants form product? Why or why not? No. There were more yellow reactants than green. LecturePLUS Timberlake

17. How do you know when a chemical reaction takes place? Color Change Precipitate Formation

18. Gas Formation Odor

19. Temperature Change Change in Acidity

20. Representing Chemical Reactions • Chemists observe chemical reactions and have come up with a way to represent or model what is happening. • Making NaCl • Solid Sodium combines with Chlorine gas to make solid Sodium Chloride: 2Na (s) + Cl2 (g)  2NaCl

21. Chemical Equations are different from Numerical Equations • Numerical Equation: 3x + 2y = 47 • Chemical Equation 2Na + Cl2 2NaCl • Reactant A + Reactant B  Product • The reactants are used up in forming the product • The arrow  shows the direction of the reaction

22. Components of a Chemical Equation Chemical Formulas Chemical Formula  2H2 + O2 2H2O Subscript Coefficient Coefficient Subscripts (Yield) (Products) (Reactants)

23. Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction ReactantsProducts MgO + C CO + Mg magnesium oxide to producecarbon monoxide reacts with carbon and magnesium LecturePLUS Timberlake

24. Law of Conservation of Matter (Mass) • Matter cannot be created or destroyed. However, it can change form. • The mass of the reactants must equal the mass of the products in a chemical reaction.

25. Balancing Chemical Equations • In other words, • The total number of each type of atom must be the same on both sides of the equation.

26. Understanding Chemical Formulas • Subscripts • BaF2the 2 in this formula is called the subscript. It refers only to the element preceding it. In this case the F (fluorine).

27. Understanding Chemical Formulas • Parentheses • Al(NO3)3in some chemical formulas it is necessary to use parentheses. The subscript outside the parentheses refers to all the elements inside the parentheses. In this example there are: one Al (aluminum), three N (nitrogen), and nine O (oxygen).

28. Understanding Chemical Formulas • Coefficients • 3BaF2the 3 in this formula is called the coefficient. It refers to each element that follows. In this case there would be 3 Ba (barium) and 3 F2(a total of 6 fluorine).

29. Reaction Rates • Increasing Temperature increases reaction rate • Surface Area – increasing the surface area increases the rate of reaction. • Concentration – amount of reactants in a given volume. • Stirring increases reaction rate

30. Reaction Rates - Catalysts • Catalyst – speeds up a reaction but does not change during the reaction • Catalysts do not get used up in a reaction HCl • CH3COCH3 + I2 CH3COCH2I + HI • HClis a catalyst, necessary for the reaction but not used up in the reaction, that is why it is written above the reaction arrow.

31. Reaction Rates • Increasing reactants increases the rate of reaction and increases the products made • Reactions will occur until at least one of the reactants is all used up • Mass of all the reactants is equal to the mass of all the products

32. Reaction Rates - Spectrophotometer • Spectrophotometer measures absorbance or transmission of light • Can be used to measure the disappearance or appearance of products or reactants in a chemical reaction