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Chapter 6

Chapter 6. Chemical Reactions and Equations. Warm-up. Who can recall what the 4 pictures were on the intro slide for this chapter?. Fire. Two flasks (one with a blue liquid and one with a yellow liquid). Test tube with a blue solid substance. Smoke trail.

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Chapter 6

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  1. Chapter 6 Chemical Reactions and Equations

  2. Warm-up Who can recall what the 4 pictures were on the intro slide for this chapter? Fire Two flasks (one with a blue liquid and one with a yellow liquid) Test tube with a blue solid substance Smoke trail What do all of these things have to do with chapter 6? They all show signs of a chemical change

  3. Indications of a Chemical Change Chemical Change The change of one or more substances into new substances by the rearrangement of atoms. Change in energy Change in color Formation of a Precipitate (two liquids combine and a solid is produced) Formation of a gas

  4. Parts of a Chemical Equation Reactants Products Coefficients Physical States (solid, liquid, gas or aqueous)

  5. Writing Equations Word Equations Using the names of chemicals to describe chemical reactions Chemical Equations Using chemical formulas and numbers to describe chemical reactions Hopefully you noticed that this equation defies the Law of Conservation of Matter. It is not balanced. Once you master writing equations, you will also learn how to balance equations.

  6. Practice ProblemsUse your ion tables Re-write the following chemical equation in words Solid calcium chromate + aqueous calcium chloride + Aqueous lithium chromate aqueous lithium chloride Re-write the following word equation as a chemical equation Solid copper + fluorine gas = solid copper (II) fluoride Cu(s) + F2(g) CuF2 (s)

  7. Energy When chemical reactions take place, energy is either absorbed or released in the process An endothermic reaction + energy An exothermic reaction

  8. Warm up Watch the following video to complete the warm up http://www.youtube.com/watch?v=R6bBs2D0cpA Write the following chemical equation for the reaction that occurred in the video: Aluminum + iodine = aluminum iodide You should be able to answer the following questions: What are the reactants? What are the products? What was the indication that a chemical change took place? Was this an endotherm or exothermic reaction?

  9. Physical States of Elements • Metals • Metals are always represented by their symbols from the periodic table, with no subscripts • All metals, with the exception of mercury are solid and will have an (s) following their symbols in an equation Cu(s) • Non-metals • Are often diatomic (Br,I,N,Cl,H,O,F) so they will have a subscript of 2. • Most of these diatomic elements will be a gas except iodine (s) and bromine (l) Cl2(g)

  10. Physical States of Ionic Compounds • Ionic Compounds • Their physical state will be • (aq) = aqueous if they can dissolve in water (soluble) • (s) = solid if they can’t (insoluble) Use this table to determine the solubility of ionic compounds:

  11. More Practice Problems What would be the physical states of the following substances if written in a chemical equation? (s) (aq) PbI2 __________ KNO3 ____________ KI __________ Pb(NO3)2 ____________ (aq) (aq) Write the following equation with physical states: Lead (II) nitrate combines with potassium iodide to form potassium nitrate and lead (II) iodide. Pb(NO3)2(aq) + KNO3(aq) + KI(aq) PbI2(s)

  12. Warm-up Write the chemical equation for the reaction: (Use a solubility table to predict the physical states of each compound) potassium iodide + lead (II) nitrate = potassium nitrate and lead (II) iodide Watch the following video to see what happens http://www.youtube.com/watch?v=BhO8kGrc4dg Did you write the correct physical state for each compound in the reaction?

  13. Balancing Chemical Equations Why? To demonstrate the Law of Conservation of Mass which states: In a chemical reaction mass is neither created or destroyed Antoine Lavoisier What must be conserved? The number and type of atoms 2 sodium atom + 2 chlorine atoms = 2 sodium atoms + 2 chlorine atoms

  14. How to Balance a Chemical Equation • Make sure that both sides of an equation have an equal number of each type of atom represented. • Balance equations by adding coefficients. • Never mess with subscripts Na Cl Mg Br

  15. Strategies for Balancing Chemical Equations 1. The even/odd combination Make the subscript of one, the coefficient of the other and vice versa. Iron (III) oxide Iron + Oxygen Practice:

  16. Strategies Continued 2. Balance groups as a whole if the elements of the group are only represented in the group on each side of the equation. Mg OH Al Practice:

  17. Strategies Continued 3. Balancing Hydrocarbon Combustion Reactions The first step is to add a coefficient to the hydrocarbon so that the total number of hydrogens in the molecule is divisible by four. Then, balance the product side of the equation before finishing up with oxygen. C H O Practice:

  18. Strategies Continued • Splitting Water When hydroxide shows up on one side of an equation and water is on the other side, split water into H(OH) to balance out hydroxide. Practice:

  19. Things to Keep in Mind • Again, do not mess with subscripts • In the final solution, the coefficients have to be in the lowest whole number ratio. • If at first you don’t succeed, try, try again! Most of the solutions to these problems come from trial and error.

  20. Comprehensive Practice Problem • Write the equation • Note the physical state of each substance • Balance the equation Potassium chromate combines with lead (II) nitrate to form potassium nitrate and lead (II) chromate

  21. Warm-up If I put all the reactants of the following equation into the left side of the balance and all of the products into the right side, why would the balance look like this?

  22. Types of Chemical Reactions • 5 General Types • Synthesis • Decomposition • Single displacement • Double displacement • Combustion You will need to know how to identify these reactions

  23. Types of Chemical Reactions – 5 General Formulas Combustion CxHy + O2 CO2 + H20 Synthesis A + B AB (Two elements combine to form a compound) Decomposition AB A + B (One compound splits to form two compounds) Always the products of these combustion reactions

  24. Reactions Cont. Single Replacement (Single Displacement) A + BC AC + B (Metals replace metals and non-metals replace non-metals) Double Replacement (Double Displacement) AB + XY AY + XB (Compounds switch partners)

  25. Practice Problems Combustion Decomposition Single replacememt Synthesis Double Replacement Identify the type of reaction

  26. Warm-up What type of reaction does the picture represent? What are the reactants in this reaction? Which one will run out first?

  27. Equilibrium http://www.youtube.com/watch?v=JsoawKguU6A • Many reactions can change direction. • These are called reversible reactions. • When no net change occurs in the amount of reactants and products, a system is said to be in equilibrium. • A system in which opposite actions are taking place at the same rate, it is said to be in dynamic equilibrium. • Products and reactants are forming at the same rate. • Reactants are never fully used up because they are constantly being formed from products.

  28. How fast do reactions reach equilibrium? • The amount of energy the particles must have when they collide is called the activation energy of that reaction. • The speed of reaction measures how quickly the reactants disappear or how quickly the products appear. • The amount of substance changed per unit time is the rate of reaction. Reaction Rate http://www.bing.com/videos/search?q=activation+energy+video&mid=CC5874704F3D6F93469CCC5874704F3D6F93469C&view=detail&FORM=VIRE7

  29. Temperature affects the rate of reaction also. • The higher the temperature, the faster the reaction; the lower the temperature, the slower the reaction. • The amount of substance present in a certain volume is called the concentration of the substance. • Raising the concentration of a reactant will speed up a reaction because there are more particles per volume • When one reactant is used up, the reaction will stop • The reactant that is used up first is called the limiting reactant Factors that Affect the Rate of a Reaction

  30. Presence of a catalyst speeds up the rate of a reaction without being permanently changed of used up itself. • A catalyst speeds up the reaction by lowering the activation energy. • Biological catalysts are called enzymes. • Reactions that have undesirable products sometimes have to be slowed down. • A substance that slows down a reaction is called an inhibitor. Factors that Affect the Rate of a Reaction

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