Chapter 8 Chemical Reactions I. Nature of Chemical Reactions reactant – substance(s) that enters a reaction, on the left of a chemical equation product – substance(s)
Download ReportTranscript Chapter 8 Chemical Reactions I. Nature of Chemical Reactions reactant – substance(s) that enters a reaction, on the left of a chemical equation product – substance(s)
Chapter 8 Chemical Reactions I. Nature of Chemical Reactions reactant – substance(s) that enters a reaction, on the left of a chemical equation product – substance(s) produced by a reaction, on the right of a chemical equation KI + Pb(NO3)2 ---> PbI2 + KNO3 Looking at the reaction here... – What are the reactants? – What are the products? – …and the blast from the past…. What is wrong with it? II. Balancing Chemical Equations Chemical reactions are described by chemical equations which must be balanced A balanced equation has the same # of atoms of each element on each side of the arrow! –C + O2 --> CO2 –2H2 + O2 --> 2H2O II. Balancing Chemical Equations Matter can neither be created nor destroyed We know that a chemical reaction must have the same amount of material after as it had before because of the conservation of mass Def – the observation that mass remains constant in a chemical reaction is known as the conservation of mass II. Balancing Chemical Equations To balance a chemical equation: – Do an atom count. Count each element’s atoms on each side of the equation. WRITE THE ELEMENTS IN THE SAME ORDER ON BOTH SIDES!!! – Check to see if it’s already balanced. If it is, stop. – If not, find the most complicated compound. – Starting w/that compound, go element by element through that side of the equation, balancing each element by adding coefficients (“playing tennis”). – If an element is repeated more than once on one side of an arrow, save it for last. II. Balancing Chemical Equations Balance the following: Na + MgF2 --> NaF + Mg N + O2 --> KCl + Pb(NO3)2 --> NO2 KNO3 + PbCl2 II. Balancing Chemical Equations Balance the following: 2Na + MgF2 --> 2NaF + Mg N + O2 --> 2KCl + Pb(NO3)2 --> NO2 BALANCED!!! 2KNO3 + PbCl2 Balance These! Mg + HCl --> MgCl2 + H2 N2 + H2 --> NH3 H2O2 --> H2O + O2 Al + O2 --> Al2O3 HCl + NaOH --> NaCl + H20 KClO3 --> KCl + O2 Al + NiBr2 --> AlBr3 + Ni CaSO4 + AlBr3 --> CaBr2 + Al2(SO4)3 Mg Balance These! + 2HCl --> MgCl2 + H2 N2 + 3H2 --> 2NH3 2H2O2 --> 2H2O + O2 4Al + 3O2 --> 2Al2O3 HCl + NaOH --> NaCl + H20 2KClO3 --> 2KCl + 3O2 2Al + 3NiBr2 --> 2AlBr3 + 3Ni 3CaSO4 + 2AlBr3 --> 3CaBr2 + Al2(SO4)3 III. Types of Chemical Reactions Synthesis Reaction - 2 or more simple substances coming together to form a new, more complex one –2Na + Cl2 ---> 2NaCl –the Na and Cl came together to form NaCl –It’s kind of like two people getting married Britney Spears married K-Fed III. Types of Chemical Reactions Decomposition reaction - complex substance being broken down into 2 or more simpler ones –H2CO3 ---> H20 + CO2 –the complex H2CO3 broke up into the simpler H20 and CO2 –It’s kind of like 2 people getting a divorce Britney and K-Fed split up III. Types of Chemical Reactions Single-Replacement Reaction - an uncombined element replaces another element in a compound –2Na + 2H20 ---> 2NaOH + H2 –if you look, you’ll see that Na kicked the H out of water to form NaOH--it replaced it – It’s kind of like when one person breaks up with someone to go out with someone else. Brad Pitt left Jennifer Aniston for Angelina Jolie III. Types of Chemical Reactions Double-Replacement Reaction - different atoms in 2 different compounds replace each other – 2KCl + Pb(NO3)2 ---> 2KNO3 + PbCl2 – the K and Pb each switched partners! – the K had Cl, but it traded Cl for NO3 – the Pb had NO3, but it traded NO3 for Cl – It’s kind of like if… Jessica Simpson & Nick Lachey and Britney Spears & K-Fed decided that it would be better if Jessica was with K-Fed and Britney was with Nick Balance and Classify: AlBr3 + Ni ---> Al + NiBr2 Al + O2 ---> Al2O3 KCl + O2 ---> KClO3 NaCl + H20 ---> HCl + NaOH (NH4)2SO4 + Ba(NO3)2 ---> BaSO4 + NH4NO3 MgCl2 + H2 ---> Mg + HCl H2 + O2 ---> H20 NaCl ---> Na + Cl2 CaCl2 + F2 ---> CaF2 + Cl2 AgCl + KNO3 ---> AgNO3 + KCl Balance and Classify: 2AlBr3 + 3Ni ---> 2Al + 3NiBr2 4Al + 3O2 ---> 2Al2O3 2KCl + 3O2 ---> 2KClO3 NaCl + H20 ---> HCl + NaOH (NH4)2SO4 + Ba(NO3)2 ---> BaSO4 + 2NH4NO3 MgCl2 + H2 ---> Mg + 2HCl 2H2 + O2 ---> 2H20 2NaCl ---> 2Na + Cl2 CaCl2 + F2 ---> CaF2 + Cl2 AgCl + KNO3 ---> AgNO3 + KCl IV. Energy of Chemical Reactions Exothermic Reactions - reactionsExothermic that or release energy Endothermic? – reactants have more energy than products – the energy released is often heat – CH4 + 2O2 ---> CO2 + 2H20 + energy Endothermic Reactions - reactions in which energy is absorbed – products have more energy than reactants – 2NaCl + energy ---> 2Na + Cl2 IV. Energy of Chemical Reactions Activation Energy - energy required to “jump start” a reaction, it’s the hill on an energy diagram Classify these as Exothermic or Endothermic energy is released reactants have more energy than the products energy is a reactant an explosion the reaction’s beaker cools products have more energy than the reactants reactants have less energy than the products V. Rates of Chemical Reactions Reaction rate - how quickly reactants turn to products Collision theory - molecules react when they collide (like bumper cars!) V. Rates of Chemical Reactions to make a reaction go faster, cause more collisions! – increase the concentration - the more molecules there are, the more collisions there are – increase the surface area - if you powder the reactants, then there are more molecules exposed on the surface rather than trapped inside a lump – increase the temp. - causes molecules to move faster, thus there are more collisions – add a catalyst - a catalyst is a chemical that lowers the activation energy (the hill on the energy diagram) rxn rate rxn rate Fill in these graphs! particle size rxn rate rxn rate concentration temperature am’t of catalyst rxn rate rxn rate Fill in these graphs! particle size rxn rate rxn rate concentration temperature am’t of catalyst rxn rate rxn rate Fill in these graphs! particle size rxn rate rxn rate concentration temperature am’t of catalyst rxn rate rxn rate Fill in these graphs! particle size rxn rate rxn rate concentration temperature am’t of catalyst rxn rate rxn rate Fill in these graphs! particle size rxn rate rxn rate concentration temperature am’t of catalyst