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Regents Chemistry

Regents Chemistry. Chemical Reactions: An Introduction. Physical vs. Chemical Properties. Substances are described by their physical and chemical properties Physical properties describe how it looks, smells and feels. No change in composition occurs!

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Regents Chemistry

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  1. Regents Chemistry • Chemical Reactions: An Introduction

  2. Physical vs. Chemical Properties • Substances are described by their physical and chemical properties • Physical properties describe how it looks, smells and feels. No change in composition occurs! • ex – color, odor, volume and state of matter • Chemical properties describe the substances ability to form new substances • ex – ability of wood to burn, metal to rust, food to digest

  3. Examples of Properties • Classify each as a physical or chemical property • 1. Boiling point of ethanol • 2. The hardness of a diamond • 3. Sugar ferments to form alcohol • 4. A metal wire conducts electricity

  4. Physical vs. Chemical Changes • A physical change is a change in one or more physical properties, but no change in the fundamental components that make up the substance. Most common are changes of state • A Chemical change is a change in fundamental components, a change into a new substance. Called reactions!

  5. Examples • Classify each of the following as a physical or chemical change • Melting of ice into boiling of water • Electrolysis of water • Iron metal is melted • Tarnishing of silver • Breaking a rock into pieces  Worksheet

  6. Regents Chemistry • Chemical Reactions

  7. What’s a Chemical Reaction? • Chemical reactions are part of our everyday life Natural gas is burned to heat houses Steel on cars rusts Plastic is made for all kinds of uses Mini-hot packs are used to keep Us warm outdoors!

  8. How Do We Know a Reaction Occurs? • Chemical reactions often give visible clues • Demos silver nitrate and potassium chloride Methane gas and oxygen Mini-heat packs

  9. Evidence of a Reaction • Some of the BIG clues.. • 1. The color changes • Bunsen Burner • 2. A solid forms • silver nitrate and potassium chloride • 3. Bubbles form • zinc metal and HCl • 4. Heat and/or a flame is produced, or heat is absorbed • Mini-heat packs

  10. What’s involved in a reaction? • Chemical reactions have (2) parts • The Reactants and the Products Reactants are on the left side of the equation and shows what goes into the reaction! Products are on the right side of the equation and shows what comes out of the reaction! Example K + H2O  H2 + KOH

  11. Reactants/Products Have Physical States! • We look at our previous example… K + H2O  H2 + KOH (s) (l) (g) (aq) • We place the abbreviation for the state • After each chemical formula • Symbol State • (s) solid • (l) Liquid • (g) gas • (aq) aqueous (dissolved in water)

  12. Writing Unbalanced Chemical Equations • We will start by writing basic chemical equations from word problems • Example: Solid carbon reacts with gaseous oxygen to form gaseous carbon dioxide Reactants = solid carbon + gaseous oxygen Products = gaseous carbon dioxide C(s) + O2(g) CO(g)

  13. Example #2 • Solid zinc metal reacts with hydrochloric acid to produce bubbles of hydrogen gas and aqueous zinc chloride Zn(s) + HCl(aq) H2(g) + ZnCl2(aq) You must use the naming compound rules To figure out how to write the chemical formulas Remember- some gases are always diatomic H2 , O2 , Cl2 worksheet

  14. Exothermic and Endothermic Processes • Exothermic processes release energy • Example: Burning of wood • Endothermic processes absorb energy • Example: Cold packs!

  15. Regents Chemistry • Balancing Chemical Equations

  16. BALANCING CHEMICAL EQUATIONS • RECAP • All forward equations are written with reactants of the left an products on the right • Example: 2H2 + O2 2H2O 4 atoms of H in product Coefficient means 2 molecules of H2, 4 atoms total Subscript means 2 atoms of H

  17. BALANCING CHEMICAL EQUATIONS • Atoms are neither created or destroyed… • so all equations must be balanced! • RULES FOR BALANCING EQUATIONS • Cannot change subscripts • 2. Can change coefficients

  18. BALANCING CHEMICAL EQUATIONS • Examples – Balance this equation • Na(s) + H2O(l) NaOH(aq) + H2(g) 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) Worksheet

  19. Regents Chemistry • Writing and Balancing Equations

  20. Regents Chemistry • Types of Reactions

  21. Types of Reactions • Although we cannot classify all reactions into distinct categories…there are four major types of reactions you should know • Synthesis (combination) Reactions • Decomposition (analysis) Reactions • Single Replacement Reactions • Double Replacement Reactions

  22. Synthesis (combination) Reactions • A reaction is classified as a synthesis reaction when two or more reactants combine and a single product is formed B + G  BG 4Fe(s) + 3O2(g) 2Fe2O3(s)

  23. Decomposition (analysis) Reactions • Decomposition reactions are the reverse of combination reactions • Occur when one substance breaks down into simpler substances BG  B + G CaCO3(s) CaO(s) + CO2(g)

  24. Regents Chemistry Single and Double Replacement Reactions

  25. Single Replacement Reactions • Involves an element and a compound • Occurs when a metal displaces the metal in a compound B2 + B1G  B2G + B1 Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s) Not all metals will displace (react with) a metal in a compound..so how do we know if a reactions will occur? …we use our Table J in our reference tables!

  26. Predicting if a Reaction Will Occur • Table J (Activity Series) on p. 4 is arranged so that a metal listed on the table will react with the compound of a metal that is below it • For Example: Zn will react with a compound of copper Zn(s) + Cu(NO3)2 Cu(s) + Zn(NO3)2(aq) But because Cu is below Zn on the table, it will not react with compounds of Zn Cu(s) + Zn(NO3)2 no reaction

  27. So.. • So..above it will bump it… below it will not! • The MORE ACTIVE will bump the LESS ACTIVE

  28. Predicting if a Reaction Will Occur • There is one element on the table that is not a metal…Hydrogen ion (H+)! • All metals above hydrogen will react with acids to release hydrogen gas and produce a salt Mg(s) + 2HCl(aq) H2(g) + MgCl2(aq)

  29. Predicting if a Reaction Will Occur • In the 2nd column of Table J is a list of nonmetals • A nonmetal will replace a less active nonmetal in a compound according to the equation G1 + BG2 BG1 + G2 For example..Fluorine is listed as the most active nonmetal, and it will replace chlorine, bromine and iodine from other binary compounds F2(g) + 2NaCl(aq) Cl2(g) + 2NaF(aq) Cl is below F so it will not react! Cl2(g) + NaF  no reaction

  30. Practice Problems • Predict if reactions will occur and write the the products or NR for NO REACTION: • Ca(s) + AgNO3(aq) • Pb(s) + Al(NO3)3(aq) • Cr(s) + Pb(NO3)2(aq) • Co(s) + HCl(aq) --> CaNO3(aq) + Ag(s) --> NR --> Cr(NO3)2(aq) + Pb(s) --> CoCl2(aq) + H2(g)

  31. Double Replacement Reactions • Double replacement reactions generally involve two soluble ionic compounds that react in solution to produce a precipitate, a gas, or a molecular compound such a water • Represented by the equation: B1G1 + B2G2 B1G2 + B2G1

  32. Predicting if a Reaction Will Occur in a Double Replacement Reaction • Three general situations in which a double replacement reaction will occur • 1. If a solid (precipitate) is formed • We look at Table F (p.2) in the reference tables and check the solubility of the two compounds Ex: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) The reaction will occur because AgCl is insoluble meaning, it will not stay dissociated in solution

  33. Soluble vs. Insoluble • Soluble means the substance will stay as ions in the solution (just floating around!)…no reaction will happen! • Insoluble means it will form a solid, gas or molecular compound (such as water) and not stay as ions…a reaction will occur!

  34. Predicting a Reaction... • 2. If a gas is formed Na2S(aq) + 2HCl(aq) H2S(g) + 2NaCl(aq) • If a molecular substance, such as H2O is formed NaOH(aq) + HCl(aq) H2O(l) + NaCl(aq)

  35. Practice Predicting..Will a Reaction Occur? Ca(NO3)2(aq) + KCl(aq) CaCl2(aq) + KNO3(aq) = NR Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + NaNO3(aq)

  36. REGENTS CHEMISTRY • Determining Missing Mass in Equations

  37. The Law of Conservation of Mass • The Law of Conservation of mass states that matter cannot be created nor destroyed • This is very useful when considering chemical reactions • WHY? • When given a balanced equation in which either the reactant or product is missing, we can determine the formula of the missing substance..this we have done!

  38. Missing Formulas in Equations K + ___________ = KCl There must be a Cl in the reactants because it appears in the products

  39. Missing Mass in Equations • Just as the formula of a missing reactant or product can be determined, the mass of a missing substance can also be found! • TOTAL MASS BEFORE = TOTAL MASS AFTER • HOW???? USING SIMPLE MATH!

  40. EXAMPLE • If 103.0 g of potassium chlorate is decomposed to form 62.7 g of potassium chloride and oxygen gas, how many grams of oxygen are formed? 2KClO3(aq) --> 2KCl(aq) + 3O2(g) 1. Find the total mass of the reactants 2. The total mass of the reactants must equal the total mass of the products

  41. EXAMPLE cont.. 2KClO3(aq) --> 2KCl(aq) + 3O2(g) mass of KCLO3 = mass of KCl + mass of O2 103.0g = 62.7g + mass O2 mass O2 = 103.0g - 62.7g mass O2 = 40.3g

  42. Example #2 • What mass of carbon dioxide will be produced if 144g of carbon react with 384 g oxygen gas? C(s) + O2(g) --> CO2(g) Mass C + mass O2 = mass CO2 144g C + 384g O2 --> mass CO2 528g = mass CO2 worksheet

  43. Unknown Reactants and Products • Just like we can find missing mass, we can also identify missing reactants or products in a formula • Remember 2 steps • Whatever is on the left side must also be on the right side..this tells you what us missing! • Think about the type of formula..this will help you complete the equation!

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