1. Success Starter! 1.What was the point of the last unit about bonds? 2.How can you apply bonds to your life? 3. What kinds of jobs are related to bonding?

2. Chemical Reactions

3. The Nature of Chemical Reactions Chemical reactions occur when substances undergo chemical changes to form new substances. Signs: – Production of gas – Change of color

4. Chemical Reactions Reactants react with each other to form products. H 2 + O → H 2 O Chemical reactions rearrange atoms – O 2 and C 8 H 18 react to form CO 2 and H 2 O Why can gasoline and oxygen be in the same place without reacting?

5. Energy and Reactions Energy must be added to break bonds – Ex: heat, electricity, sound, light Forming bonds releases energy – New bonds are formed to make products

6. Energy is Conserved in Chemical Reactions Chemical energy: energy released when a chemical compound reacts to produce new compounds Total energy before the reaction is equal to the energy of the products and their surroundings – This is known as the Law of Conservation of Energy

7. Exothermic and Endothermic Reactions Exothermic Reactions: release energy – Temperature of surroundings rises because energy is released – More energy is released as products form than is absorbed to break bonds in reactants Endothermic Reactions: absorb energy – Temperature of surroundings lowers – More energy is needed to break bonds in reactants than to form bonds in products

8. Questions 1.What is a substance that undergoes a chemical change? 2. What is the substance produced by a chemical change? 3. What are two kinds of chemical reactions?

9. Objectives Distinguish among the five different types of chemical reactions. Predict the products of some reactions based on the reaction type. Describe reactions that transfer or share electrons between molecules, atoms, or ions

10. Describing Reactions Chemical equation: – A representation of a chemical reaction that uses symbols to show the relationship between the reactants and products CH 4 + O 2 → CO 2 + H 2 O Methane PLUS OxygenYIELDSCarbon Dioxide AND Water REACTANTSPRODUCTS

11. Synthesis Reaction Two or more substances combine to form a new compound. A + B → AB

13. Decomposition Reaction Single compound breaks down to form two or more simpler substances AB → A + B

14. Combustion Reaction Oxidation reaction of an organic compound, in which heat is released – “burning” Reactants: Hydrocarbon, O 2 Products: CO 2, H 2 O, heat

15. Single-Displacement Reactions One element or radical takes the place of another element or radical in a compound. AX + B → BX + A

16. Double Displacement A gas, solid, or molecular compound forms from the apparent exchange of atoms or ions between two compounds AX + BY → AY + BX

17. QUIZ Determine what type of reaction each general statement describes: XA + B → BA + X AB → A + B A + B → AB AX + BY → AY + BX

18. Type of Reaction Definition ★ Equation Synthesis Decomposition Single Replacement Double Replacement Complete the chart. A = Red B = Blue C = Green D = Yellow A + B → AB AB → A + B AB + C → AC + B AB + CD → AC + BD Two or more elements or compounds combine to make a more complex substance Compounds break down into simpler substances Occurs when one element replaces another one in a compound Occurs when different atoms in two different compounds trade places

19. Identifying Chemical Reactions ____ P + O 2 → P 4 O 10 ____ Mg + O 2 → MgO ____ HgO → Hg + O 2 ____ Al 2 O 3 → Al + O 2 ____ Cl 2 + NaBr → NaCl + Br 2 ____ H 2 + N 2 → NH 3 2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction. S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement

20. ____ Na + Br 2 → NaBr ____ CuCl 2 + H 2 S → CuS + HCl ____ HgO + Cl 2 → HgCl + O 2 ____ C + H 2 → CH 4 ____ KClO 3 → KCl + O 2 ____ S 8 + F 2 → SF 6 ____ BaCl 2 + Na 2 SO 4 → NaCl + BaSO 4

21. Factors Affecting Reaction Rates Reaction rate = how fast a chemical reaction can or will occur Factors that affect reaction rates: – Temperature: most reactions go faster at higher temperatures – Surface area: increased SA speeds up reactions – Concentration: most concentrated solutions react faster

22. Factors Affecting Reaction Rates More factors: – Pressure: Increased pressure speeds up reactions – Mass of molecules: large molecules react slower – Catalysts: speed up chemical reactions

23. What is a catalyst? a substance that changes the rate of a chemical reaction without being consumed or changed in the reaction. Most speed up chemical reactions. Inhibitors are catalysts that slow chemical reactions.

24. Enzymes Enzymes are proteins that are biological catalysts. They speed up processes in living things. Enzymes are very specific. – Most control only one chemical reaction. Enzymes must have a specific substrate (area in a molecule) to attach to for a reaction to occur. If the substrate is not available, the enzyme will not work as a catalyst.

25. 6.3 Balancing Chemical Equations

26. Describing Reactions Chemical equation: – A representation of a chemical reaction that uses symbols to show the relationship between the reactants and products CH 4 + O 2 → CO 2 + H 2 O Methane PLUS OxygenYIELDSCarbon Dioxide AND Water REACTANTSPRODUCTS

27. Describing Reactions Balanced Chemical Equations are Important! – They tell us how much of each reactant it takes to make a product – They tell us how much product is made in a reaction Balanced chemical equations also follow the Law of Conservation of Mass – Mass cannot be created nor destroyed in a chemical reaction

28. Describing Reactions A chemical equation is said to be balanced when there are the same number of atoms of every kind on both the reactant and product sides H 2 (g)+ O (g) H 2 O (l) Symbols commonly used in chemical equations: Solid (s) Liquid (l) Gas (g) Aqueous solution (aq) Catalyst H2SO4 Escaping gas ( ↑ ) Change of temperature (Δ)

29. Balancing Equations You may add coefficients in front of the compounds CANNOT change subscripts Changing the subscript changes the compound!!!! Coefficient 2H 2 O Subscript

30. Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the number of molecules of the compound.

31. Steps to a Balanced Equation There are 5 basic steps : 1.Determine the number of atoms for each element. 1.Pick an element that is not equal on both sides of the equation. 3. Add a coefficient in front of the formula with that element and adjust your counts.

32. Steps to a Balanced Equation 4. Continue adding coefficients to get the same number of atoms of each element on each side. 5. Check your answer to see if: – The numbers of atoms on both sides of the equation are now balanced. – The coefficients are in the lowest possible whole number ratios. (reduced)

33. WHAT?! Don’t fret, we are going to practice this A LOT!

34. Helpful Hints on Balancing Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last. IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

35. 1.Write the equation that describes the burning of magnesium in air to form magnesium oxide. Balancing Practice Problems Mg+O2O2 MgO Magnesium + Oxygen (air) → Magnesium Oxide Mg=1 O=2O=1 Not Balanced Need 2 O 2 2 Equation is Balanced! 2 2 2

36. Potassium metal reacts violently with water to produce potassium hydroxide and hydrogen gas. Balancing Practice Problems Potassium + Water → Potassium Hydroxide + Hydrogen Gas K + H2OH2O KOH + H2H2 K=1 H=2 O=1 K=1 H=3 O=1 2 4 2 4 2 2 2 2 2 Every element is balanced and coefficients are in the simplest form.

37. Calcium oxide, an ingredient in cement, combines with water to produce calcium hydroxide. Balancing Practice Problems Calcium oxide + Water → Calcium Hydroxide CaO+H2OH2OCa(OH) 2 Ca=1 H=2 O=2 Ca=1 H=2 O=2 After counting atoms on both sides of the equation, we find this balanced!

38. Balance these chemical equations: 1. Sn + NaOH → Na 2 SnO 2 + H 2 1. Al + Fe 3 O 4 → Al 2 O 3 + Fe 1. SbCl 5 + H 2 O → SbOCl 3 + HCl 1. P 4 O 10 + H 2 O → H 3 PO 4 1. PCl 5 + H 2 O → H 3 PO 4 + HCl 2 8349 64 45 2