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Chapter 5 Chemical Reactions. Chemical Reaction Another name for a chemical change Another name for a chemical change New properties when you are done.

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Presentation on theme: "Chapter 5 Chemical Reactions. Chemical Reaction Another name for a chemical change Another name for a chemical change New properties when you are done."— Presentation transcript:

1 Chapter 5 Chemical Reactions

2 Chemical Reaction Another name for a chemical change Another name for a chemical change New properties when you are done New properties when you are done No new atoms are made No new atoms are made Atoms are rearranged Atoms are rearranged New compounds can be made New compounds can be made Old bonds are broken Old bonds are broken New bonds are formed New bonds are formed

3 Indications of Chemical Reactions New properties New properties Color change Color change Odor change Odor change New phase is made New phase is made Precipitates- solids in a liquid Precipitates- solids in a liquid Gases- bubbles in a liquid Gases- bubbles in a liquid Two parts of reaction Two parts of reaction Reactants- the stuff you start with Reactants- the stuff you start with Products- the stuff you make Products- the stuff you make

4 Starting a Reaction Always takes a little energy Always takes a little energy Energy goes into breaking bonds in the reactants Energy goes into breaking bonds in the reactants Can use different forms of energy Can use different forms of energy Heat Heat Electricity Electricity Light Light

5 Forming Bonds Makes Energy Releases energy Releases energy Energy is conserved Energy is conserved Chemical Energy- energy stored in the bonds of the chemicals. Chemical Energy- energy stored in the bonds of the chemicals. Reactions have an energy change Reactions have an energy change

6 Exothermic Reactions If breaking bonds takes less energy than making them- it releases energy If breaking bonds takes less energy than making them- it releases energy Exo- outside Exo- outside therm- heat therm- heat Exothermic reactions release energy Exothermic reactions release energy Get hot Get hot Give off light Give off light Or release electricity Or release electricity

7 Chemical Energy ReactantsProducts Change is down Energy Released

8 Endothermic Reactions If breaking bonds takes more energy than making them- it absorbs energy If breaking bonds takes more energy than making them- it absorbs energy Endo- inside Endo- inside therm- heat therm- heat Endothermic reactions absorb energy Endothermic reactions absorb energy Get cold Get cold Require heat or energy or they stop Require heat or energy or they stop

9 Chemical Energy ReactantsProducts Change is up Heat is released

10 Chemical Equations Copper reacts with chlorine to form copper (II) chloride. Copper reacts with chlorine to form copper (II) chloride. In a word equation In a word equation Methane + oxygen water +carbon dioxide Methane + oxygen water +carbon dioxide Arrow means yields or makes Arrow means yields or makes The plus sign means and The plus sign means and Can use formulas Can use formulas CH 4 +O 2 CO 2 +H 2 O CH 4 +O 2 CO 2 +H 2 O

11 Balanced Equation Atoms cant be created or destroyed Atoms cant be created or destroyed All the atoms we start with we must end up with All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation. A balanced equation has the same number of each element on both sides of the equation.

12 C + O 2 CO 2 C + O 2 CO 2 This equation is already balanced This equation is already balanced What if it isnt already? What if it isnt already? C + O O C O O

13 C + O 2 CO C + O 2 CO We need one more oxygen in the products. We need one more oxygen in the products. Cant change the formula, because it describes what is Cant change the formula, because it describes what is C + O C O O

14 Must have started with two C Must have started with two C 2 C + O 2 2 CO 2 C + O 2 2 CO C + O C O O O C C

15 Rules for balancing Write the correct formulas for all the reactants and products Write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) Balance the elements one at a time by adding coefficients (the numbers in front) Check to make sure it is balanced. Check to make sure it is balanced.

16 Never Change a subscript to balance an equation. Change a subscript to balance an equation. If you change the formula you are describing a different reaction. If you change the formula you are describing a different reaction. H 2 O is a different compound than H 2 O 2 H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not. 2 NaCl is okay, Na2Cl is not.

17 Example H 2 +H2OH2OO2O2 Make a table to keep track of where you are at

18 Example H 2 +H2OH2OO2O2 Need twice as much O in the product RP H O

19 Example H 2 +H2OH2OO2O2 Changes the O RP H O

20 Example H 2 +H2OH2OO2O2 Also changes the H RP H O

21 Example H 2 +H2OH2OO2O2 Need twice as much H in the reactant RP H O

22 Example H 2 +H2OH2OO2O2 Recount RP H O

23 Example H 2 +H2OH2OO2O2 The equation is balanced, has the same number of each kind of atom on both sides RP H O

24 Example H 2 +H2OH2OO2O2 This is the answer RP H O Not this

25 Examples AgNO 3 + Cu Cu(NO 3 ) 2 + Ag AgNO 3 + Cu Cu(NO 3 ) 2 + Ag Mg + N 2 Mg 3 N 2 Mg + N 2 Mg 3 N 2 P + O 2 P 4 O 10 P + O 2 P 4 O 10 Na + H 2 O H 2 + NaOH Na + H 2 O H 2 + NaOH CH 4 + O 2 CO 2 + H 2 O CH 4 + O 2 CO 2 + H 2 O

26 Examples of Balancing Equations a) Pb(NO 3 ) 2 + K 2 CrO 4 PbCrO 4 + KNO 3 b) MnO 2 + HCl MnCl 2 + H 2 O+ Cl 2 c) C 3 H 6 + O 2 CO 2 +H 2 O d) Zn(OH) 2 + H 3 PO 4 Zn 3 (PO 4 ) 2 e) CO + Fe 2 O 3 Fe + CO 2 f) CS 2 + Cl 2 CCl 4 +S 2 Cl 2 g) CH 4 + Br 2 CH 3 Br + HBr h) Ba(CN) 2 + H 2 SO 4 BaSO 4 + HCN

27 Moles and Reactions 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O 2 dozen molecules of hydrogen and 1 dozen molecules of oxygen form 2 dozen molecules of water. 2 dozen molecules of hydrogen and 1 dozen molecules of oxygen form 2 dozen molecules of water. 2 x (6.02 x ) molecules of hydrogen and 1 x (6.02 x ) molecules of oxygen form 2 x (6.02 x ) molecules of water. 2 x (6.02 x ) molecules of hydrogen and 1 x (6.02 x ) molecules of oxygen form 2 x (6.02 x ) molecules of water. 2 moles of hydrogen and 1 mole of oxygen form 2 moles of water. 2 moles of hydrogen and 1 mole of oxygen form 2 moles of water.

28 Moles and Reactions The coefficients of balanced equations tell how many particles react The coefficients of balanced equations tell how many particles react And how many moles of particles And how many moles of particles We can make ratios with those moles We can make ratios with those moles 2 Mg + O 2 2 MgO 2 Mg + O 2 2 MgO If 2 moles of Mg react, 1 mole of O 2 will be required If 2 moles of Mg react, 1 mole of O 2 will be required 2 mol Mg or 1 mol O 2 1 mol O 2 2 mol Mg 2 mol Mg or 1 mol O 2 1 mol O 2 2 mol Mg

29 Mole ratios Can be used to figure out how many moles of products and reactants were used or made Can be used to figure out how many moles of products and reactants were used or made 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O If 6 mole of H 2 react, how many moles of water will form? If 6 mole of H 2 react, how many moles of water will form? How many moles of hydrogen are needed to react with 3.6 mole of oxygen? How many moles of hydrogen are needed to react with 3.6 mole of oxygen?

30 Mole to mole conversions 2 Al 2 O 3 Al + 3O 2 2 Al 2 O 3 Al + 3O 2 every time we use 2 moles of Al 2 O 3 we make 3 moles of O 2 every time we use 2 moles of Al 2 O 3 we make 3 moles of O 2 2 moles Al 2 O 3 3 mole O 2 or 2 moles Al 2 O 3 3 mole O 2

31 Mole to Mole conversions How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decompose? How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decompose? 2 Al 2 O 3 Al + 3O 2 2 Al 2 O 3 Al + 3O moles Al 2 O 3 2 moles Al 2 O 3 3 mole O 2 =5.01 moles O 2

32 Your Turn 2C 2 H O 2 4CO H 2 O 2C 2 H O 2 4CO H 2 O If 3.84 moles of C 2 H 2 are burned, how many moles of O 2 are needed? If 3.84 moles of C 2 H 2 are burned, how many moles of O 2 are needed? How many moles of C 2 H 2 are needed to produce 8.95 mole of H 2 O? How many moles of C 2 H 2 are needed to produce 8.95 mole of H 2 O? If 2.47 moles of C 2 H 2 are burned, how many moles of CO 2 are formed? If 2.47 moles of C 2 H 2 are burned, how many moles of CO 2 are formed?

33 Collision Theory In order to react molecules and atoms must touch each other. In order to react molecules and atoms must touch each other. They must hit each other hard enough to react. They must hit each other hard enough to react. Anything that increase these things will make the reaction faster. Anything that increase these things will make the reaction faster.

34 Things that Affect Rate Temperature Temperature Higher temperature faster particles. Higher temperature faster particles. More and harder collisions. More and harder collisions. Faster Reactions. Faster Reactions. Concentration Concentration More concentrated closer together the molecules. More concentrated closer together the molecules. Collide more often. Collide more often. Faster reaction. Faster reaction.

35 Things that Affect Rate Particle size Particle size Molecules can only collide at the surface. Molecules can only collide at the surface. Smaller particles bigger surface area. Smaller particles bigger surface area. Smaller particles faster reaction. Smaller particles faster reaction. Smallest possible is molecules or ions. Smallest possible is molecules or ions. Dissolving speeds up reactions. Dissolving speeds up reactions. Getting two solids to react with each other is slow. Getting two solids to react with each other is slow.

36 Things that Affect Rate Catalysts- substances that speed up a reaction without being used up. Catalysts- substances that speed up a reaction without being used up. Inhibitor- a substance that blocks a catalyst, slowing the reaction down Inhibitor- a substance that blocks a catalyst, slowing the reaction down Enzymes are biological catalysts- made by plants and animals to control reactions Enzymes are biological catalysts- made by plants and animals to control reactions Heat destroys most catalysts Heat destroys most catalysts

37 Reactions Some go to completion Some go to completion All the reactants get turned into products All the reactants get turned into products No reactants left No reactants left Some reactions go both directions Some reactions go both directions They are called reversible reactions They are called reversible reactions

38 Reversible Reactions 2H 2 (g) + O 2 (g) 2H 2 O(g) + energy 2H 2 (g) + O 2 (g) 2H 2 O(g) + energy 2H 2 O(g) + energy H 2 (g) + O 2 (g) 2H 2 O(g) + energy H 2 (g) + O 2 (g) 2H 2 (g) + O 2 (g) 2H 2 O(g) + energy 2H 2 (g) + O 2 (g) 2H 2 O(g) + energy

39 Equilibrium When I first put reactants together the forward reaction starts. When I first put reactants together the forward reaction starts. Since there are no products there is no reverse reaction. Since there are no products there is no reverse reaction. As the forward reaction proceeds the reactants are used up so the forward reaction slows. As the forward reaction proceeds the reactants are used up so the forward reaction slows. The products build up, and the reverse reaction speeds up. The products build up, and the reverse reaction speeds up.

40 Equilibrium Eventually you reach a point where the reverse reaction is going as fast as the forward reaction. Eventually you reach a point where the reverse reaction is going as fast as the forward reaction. This is dynamic equilibrium. This is dynamic equilibrium. The rate of the forward reaction is equal to the rate of the reverse reaction. The rate of the forward reaction is equal to the rate of the reverse reaction. The concentration of products and reactants stays the same, but the reactions are still running. The concentration of products and reactants stays the same, but the reactions are still running.

41 Equilibrium Equilibrium position- how much product and reactant there are at equilibrium. Equilibrium position- how much product and reactant there are at equilibrium. Shown with the double arrow. Shown with the double arrow. Reactants are favored Reactants are favored Products are favored Products are favored Catalysts speed up both the forward and reverse reactions so dont affect equilibrium position. Catalysts speed up both the forward and reverse reactions so dont affect equilibrium position.

42 LeChâteliers Principle Regaining Equilibrium

43 LeChâteliers Principle If something is changed in a system at equilibrium, the system will respond to undo that change. If something is changed in a system at equilibrium, the system will respond to undo that change. Three types of changes are described. Three types of changes are described.

44 Changing Concentration If you add reactants (or increase their concentration). If you add reactants (or increase their concentration). The forward reaction will speed up. The forward reaction will speed up. More product will form. More product will form. Equilibrium Shifts to the right Equilibrium Shifts to the right Reactants products Reactants products

45 Changing Concentration If you add products (or increase their concentration). If you add products (or increase their concentration). The reverse reaction will speed up. The reverse reaction will speed up. More reactant will form. More reactant will form. Equilibrium Shifts to the left Equilibrium Shifts to the left Reactants products Reactants products

46 Changing Concentration If you remove products (or decrease their concentration). If you remove products (or decrease their concentration). The reverse reaction will slow down The reverse reaction will slow down More product will form. More product will form. Equilibrium reverseShifts to the right Equilibrium reverseShifts to the right Reactants products Reactants products

47 Changing Concentration If you remove reactants (or decrease their concentration). If you remove reactants (or decrease their concentration). The forward reaction will slow down. The forward reaction will slow down. More reactant will form. More reactant will form. Equilibrium Shifts to the left. Equilibrium Shifts to the left. Reactants products Reactants products Used to control how much yield you get from a chemical reaction. Used to control how much yield you get from a chemical reaction.

48 Changing Temperature Reactions either require or release heat. Reactions either require or release heat. Endothermic reactions go faster at higher temperature. Endothermic reactions go faster at higher temperature. Exothermic go faster at lower temperatures. Exothermic go faster at lower temperatures. All reversible reactions will be exothermic one way and endothermic the other. All reversible reactions will be exothermic one way and endothermic the other.

49 Changing Temperature As you raise the temperature the reaction proceeds in the endothermic direction. As you raise the temperature the reaction proceeds in the endothermic direction. As you lower the temperature the reaction proceeds in the exothermic direction. As you lower the temperature the reaction proceeds in the exothermic direction. Reactants + heat Products at high T Reactants + heat Products at high T Reactants + heat Products at low T Reactants + heat Products at low T

50 Changes in Pressure As the pressure increases the reaction will shift in the direction of the least gases. As the pressure increases the reaction will shift in the direction of the least gases. At high pressure 2H 2 (g) + O 2 (g) 2 H 2 O(g) At high pressure 2H 2 (g) + O 2 (g) 2 H 2 O(g) At low pressure 2H 2 (g) + O 2 (g) 2 H 2 O(g) At low pressure 2H 2 (g) + O 2 (g) 2 H 2 O(g)


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