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Chemical Reactions and Equations

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Chemical Reactions and Equations

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  1. Chemical Equations &Reactions

  2. Let’s see what will we learn. Chemical reactions Chemical equations Chemical equations • Combination • Decomposition • Displacement • Double displacement • Balancing equations • Predicting products • from reactants

  3. Describing a Chemical Reaction • A chemical reaction is a chemical change or basically a process by which some substances (known as reactants) form some other new substances (known as products). • We can not touch chemical reaction, but can feel the effects of it.

  4. Signs of Chemical Reactions • There are five main signs that indicate a chemical reaction has taken place: release input change in color production of gases or vapor input or release of energy change in odor difficult to reverse

  5. Defining Chemical Equation A chemical equation is a symbolic representation of a chemical reaction in terms of the chemical formulas of molecules or atoms (substances taking part in it). It is not reaction, but just a symbolic representation of it. A chemical equation consists of reactants, products, and other symbols. Let’s see an example of equation. Zn(s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)

  6. 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

  7. Chemical Equations • Because the same atoms are present • in a reaction at the beginning (reactants) • and at the end (products), the amount • of matter in a system does not change. The Law of Conservation of Matter 20% Chemical Reaction 100% 100% 80% Kotz web

  8. Chemical Equations Because of the principle of the conservation of matter (or mass), The equation must be balanced. It would have same number of atoms on both side of equation To satisfy with law of conservation of mass given by Antoine Laurent Lavoisier. Lavoisier, 1788

  9. Characteristics of Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.

  10. Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. carbon dioxide + water methane + oxygen Reactant Product O2 H2O CO2 CH4 + +

  11. Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

  12. Additional Symbols Used in Chemical Equations • Alternative to (g), but used only to indicate a gaseous product • Reactants are heated • Pressure at which reaction is carried out, in this case 2 atm • Indicates the presence of some acid, particularly diluted acid, which disassociates H+ ions • Temperature at which reaction is carried out, in this case 0 oC • Formula of catalyst, in this case manganese (IV) oxide, • used to alter the rate of the reaction D 2 atm H+ 0 oC MnO2

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

  14. 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 Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

  15. Balancing Chemical Equations An important point to remember • 2NO(g) + O2(g)  2NO2(g) • The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation. • It is a “multiplier” for every atom in the molecule. The subscript 2 in O2 (g) and NO2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).

  16. “ ” 13 13 13 2 2 2 3X + O2 2Y + Z 3X + O2 2Y + Z 6X + 13 O2 4Y + 2Z Guidelines for Balancing Chemical Equations 1) polyatomic ions first (make all even) 2) even / odd 3) single elements last 4) Hydrogen second-last and oxygen last Example: need 13 oxygen atoms Multiply by O2 = 13 2

  17. ? 6 2 3 + (NH4)3PO4 + Mg(OH)2 Mg3(PO4)2 NH4OH ammonium phosphate ammonium hydroxide magnesium phosphate magnesium hydroxide OH1- NH41+ Now you try… AlCl3 + Li2CO3  Al2(CO3)3 + LiCl 3 6 2

  18. 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

  19. 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

  20. Types of Chemical Reactions Combination Reaction A + B  AB Decomposition reaction AB  A + B Displacment reaction A + BC  AC + B element element compound compound AB + CD  AD + CB Double-displacement reaction compound compound compound compound HX + BOH  BX + HOH Neutralization reaction acid water base salt

  21. Combination Reaction 2 Na + Cl2 2 NaCl Na Na Cl Cl  Cl Cl Na Na General form: A + B  AB element or element or compound compound compound

  22. CO2 + H2O C6H12O6 + O2 H2 + O2 H2O Na + Cl2NaCl Combination Reactions Photosynthesis 6 6 6 Formation of water 2 2 Formation of salt 2 2 Generally Exothermic with some exceptions.

  23. Decomposition Reaction 2 H2O + Electric Current  2 H2 + O2 O O O O  H H H H H H H H General form: AB  A + B • Compound element or element or • compound compound

  24. H2O2 H2O + O2 electricity H2O H2 +O2 NI3N2 + I2 Decomposition Reactions Hydrogen Peroxide 2 2 Electrolysis of water 2 2 Nitrogen triiodide 2 3 Generally Endothermic

  25. Displacement and Double Displacement Reactions Displacement reaction Mg + CuSO4 MgSO4 + Cu General form: A + BC  AC + B Double displacement reaction CaCO3 + 2 HCl  CaCl2 + H2CO3 General form: AB + CD  AD + CB

  26. Ca Reactivity Series Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H Cu Hg Ag Pt Au Reactivity Series determines which element is more reactive than which element and thus, we can find out which element can displace the other. Foiled again – Aluminum loses to Calcium

  27. Predict if these reactions will occur Al + MgCl2 3 2 2 3 Mg + AlCl3 Can magnesium replace aluminum? YES, magnesium is more reactive than aluminum. Activity Series No reaction Al + MgCl2 Can aluminum replace magnesium? NO, aluminum is less reactive than magnesium. Therefore, no reaction will occur. Activity Series Order of reactants DOES NOT determine how they react. No reaction MgCl2 + Al

  28. More Displacement Reactions

  29. Aqueous barium nitrate reacts with sulfuric acid [H2SO4(aq)] to yield a barium sulfate precipitate and nitric acid [HNO3(aq)] Double Replacement Reaction Barium sulfate Nitric acid Sulfuric acid Barium nitrate + + Ba2+ SO42- H1+ NO31- H1+ SO42- Ba2+ NO31- 2 BaSO4 + Ba(NO3)2 + HNO3 H2SO4 (aq) (aq) Ba(NO3)2(aq) + H2SO4(aq) BaSO4 (ppt) + 2 HNO3(aq) + 2 H1+(aq) + 2 NO31-(aq) + 2 H1+(aq) + SO42-(aq) Ba2+(aq) + SO42-(aq) Ba2+(aq) + 2 NO31-(aq) H1+ H1+ H1+ H1+ Ba2+ Ba2+ Ba2+ SO42- SO42- NO31- NO31- SO42- NO31- NO31- R E A C T A N T S P R O D U C T S

  30. More Double - Displacement Reactions

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