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Chemical Equations & Reactions

Chemical Equations & Reactions. Physical Properties. color melting point boiling point electrical conductivity specific heat density state (solid, liquid, or gas). Physical Change. Changes in physical properties melting boiling condensation

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Chemical Equations & Reactions

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  1. Chemical Equations & Reactions

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

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

  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)

  5. Describing a Chemical Reaction Indications of a Chemical Reaction • Evolution of heat, light, and/or sound • Production of a gas • Formation of a precipitate • Color change

  6. Learning Check E1 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

  7. Solution E1 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

  8. Meaning of Chemical Formula Chemical Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

  9. Coefficients • A formula may begin with a number. • If there is no number, then “1” is understood to be in front of the formula. • This number is called the coefficient. • The coefficient represents the number of molecules of that compound or atom needed in the reaction. • For example: • 2H2SO4 – 2 molecules of Sulfuric Acid

  10. Coefficients • 2H2SO4 – 2 molecules of Sulfuric Acid • A coefficient is distributed to ALL elements in a compound • 2 – H2 (for a total of 4 H atoms) • 2 – S (for a total of 2 S atoms) • 2 – O4 (for a total of 8 O atoms)

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

  12. A Chemical Reaction Reactants Products

  13. Learning Check E2 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?

  14. Learning Check E2 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.

  15. Chemical Equations • Reactants– the substances that exist before a chemical change (or reaction) takes place. • Products– the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

  16. Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

  17. Reading A Chemical Equation 4 NH3 + 5 O2 4 NO + 6 H2O Four molecules of NH3 react with five molecules O2to produce four molecules NO and six molecules of H2O or Four moles NH3 react with 5 moles O2toproduce four moles NO and six moles H2O

  18. Reading Chemical Equations • Each side of an equation represents a combination of chemicals. • The combination is written as a set of chemical formulas, separated by + symbols. CH4 + 2 O2 → CO2 + 2 H2O Coefficient

  19. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

  20. Unbalanced and Balanced Equations H Cl Cl H H Cl H Cl Cl Cl H Cl H H H2 + Cl2 2 HCl (balanced) H2 + Cl2 HCl (unbalanced) reactants products reactants products H H 2 1 2 2 Cl Cl 2 1 2 2

  21. Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.

  22. A Balanced Chemical Equation Same numbers of each type of atom on each side of the equation Al + S Al2S3 Not Balanced 2Al + 3S Al2S3Balanced

  23. Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom 4NH3 + 5O24NO + 6H2O 4 N = 4 N 12 H = 12 H 10 O = 10 O

  24. Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom 4NH3 + 5O24NO + 6H2O 4 N = 4 N 12 H = 12 H 10 O = 10 O

  25. Steps in Balancing An Equation Fe3O4 + H2 Fe +H2O Fe:Fe3O4 + H23 Fe +H2O O:Fe3O4 + H2 3 Fe +4H2O H: Fe3O4 + 4 H2 3 Fe +4H2O

  26. Learning Check E4 Fe3O4 + 4 H2 3 Fe +4H2O A. Number of H atoms in 4 H2O 1) 2 2) 4 3) 8 B. Number of O atoms in 4 H2O 1) 2 2) 4 3) 8 C. Number of Fe atoms in Fe3O4 1) 1 2) 3 3) 4

  27. Solution E4 Fe3O4 + 4 H2 3 Fe +4H2O A. Number of H atoms in 4 H2O 3) 8 B. Number of O atoms in 4 H2O 2) 4 C. Number of Fe atoms in Fe3O4 2) 3

  28. Learning Check E5 Balance each equation. The coefficients for each equation are read from left to right A. Mg + N2 Mg3N2 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. Al + Cl2 AlCl3 1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2

  29. Learning Check E5 C. Fe2O3 + C Fe + CO2 1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 D. Al + FeO Fe + Al2O3 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 E. Al + H2SO4 Al2(SO4)3 + H2 1) 3, 2, 1, 22) 2, 3, 1, 3 3) 2, 3, 2, 3

  30. Solution E5 A. 3 Mg + N2 Mg3N2 B. 2 Al + 3 Cl2 2 AlCl3 C. 2 Fe2O3 + 3 C 4 Fe + 3 CO2 D. 2 Al + 3 FeO 3 Fe + Al2O3 E. 2 Al + 3 H2SO4 Al2(SO4)3 + 3 H2

  31. Reactants  Products Unbalanced

  32. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

  33. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide  bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl2 + NaBr  Br2 + NaCl 3) Determine the coefficients that make the equation balance. Cl2 + 2 NaBr  Br2 + 2 NaCl

  34. Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al2(SO4)3 + CaCl2 CaSO4 + AlCl3 3) Determine the coefficients that make the equation balance. Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3

  35. Showing Phases in Chemical Equations • Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) • Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) • Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g) H2O(s) H2O(l) H2O(g)

  36. Matter Is Conserved H2 + Cl2 2 HCl + + Total atoms = Total atoms 2 H, 2 Cl 2H, 2 Cl Total Mass = Total Mass 2(1.0) + 2(35.5) 2(36.5) 73.0 g = 73.0 g

  37. Law of Conservation of Mass In any ordinary chemical reaction, matter is not created nor destroyed

  38. Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2 2 NaCl Na Cl Na+ Cl - Cl Cl - Na+ Na General form: A + B  AB element orelement orcompound compoundcompound

  39. You try… • Al + Br2→ AlBr3 Is it balanced? • 2 Al + 3 Br2→ 2 AlBr3 • H2 + SO3 → H2SO4 Balance it… • 3H2 + 4SO3 → 3H2SO4

  40. Decomposition Reaction Decomposition reaction 2 H2O + 2 H2 O2 H O H H O H + O H O H H H General form: AB A + B compound two or more elements or compounds

  41. Single and Double Replacement Reactions Single-replacement reaction Mg + CuSO4 MgSO4 + Cu General form: A + BC  AC + B Double-replacement reaction CaCO3 + 2 HCl  CaCl2 + H2CO3 General form: AB + CD  AD + CB

  42. Activity Series Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Ca Foiled again – Aluminum loses to Calcium Halogen Reactivity F2 Cl2 Br2 I2

  43. Potassium reacts with Water P O W !

  44. Double Replacement Reaction

  45. How do you know if a Double Displacement Reaction Occurred? • A new gas • Formation of a precipitate • Neutralization of an acid and base.

  46. Formation of a solid: AgCl AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)

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