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Reactions and Stoichiometry Chapters 11-12. Reactions Reactants Products.

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Presentation on theme: "Reactions and Stoichiometry Chapters 11-12. Reactions Reactants Products."— Presentation transcript:

1 Reactions and Stoichiometry Chapters 11-12

2 Reactions Reactants Products

3 Balancing Reactions Reactions must maintain conservation of mass, charge, and energy Reactants and Products must have the same number of atoms of each element 2H 2 + O 2 2H 2 O

4 Balancing Reactions Reactions must maintain conservation of mass, charge, and energy Reactants must have the same total charge as Products Cu +1 + Fe +3 Cu +2 + Fe +2

5 Balancing Reactions To balance a reaction: Do NOT change chemistry (compounds, subscripts) Only change coefficients (big numbers in front of chemicals) Coefficients can only be whole numbers 2H 2 + O 2 2H 2 O

6 Balancing Reactions 4Na + O 2 2Na 2 O 2Al + 3Br 2 2AlBr 3 4Ni + 3O 2 2Ni 2 O 3 2HNO 3 + Ca(OH) 2 Ca(NO 3 ) 2 + 2H 2 O

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8 Reaction Types Synthesis Decomposition Single Replacement Double Replacement Combustion

9 Synthesis Chemical change in which two or more substances react to form a single new substance (1 product) Also called Combination 2Mg + O 2 2MgO

10 Decomposition Chemical change in which a single compound breaks down into two or more simpler products 1 reactant NaHCO 3 NaOH + CO 2

11 Single Replacement Chemical change in which one element replaces a second element in a compound Metal replaces metal (hydrogen included) Nonmetal replaces nonmetal Zn + 2HCl ZnCl 2 + H 2

12 Double Replacement Chemical change involving an exchange of positive ions between compounds AgNO 3 + NaCl NaNO 3 + AgCl

13 Combustion Chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light 2Mg + O 2 2MgO

14 Combustion Complete combustion of a hydrocarbon produces carbon dioxide and water 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

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16 Spontaneous Reactions A single replacement reaction will only occur if: The single element in the reactants is more active than the element it replaces in the compound

17 Table J The more active element: Does not want to be alone Wants to be combined with someone else

18 Spontaneous or not? ZnCO 3 + Mg MgCO 3 + Zn PbSO 4 + Mn MnSO 4 + Pb 3KNO 3 + Al Al(NO 3 ) 3 + 3K 2HCl + Zn ZnCl 2 + H 2 2NaBr + I 2 2NaI + Br 2 YES NO YES NO

19 Spontaneous Reactions A double replacement reaction will only occur if: A precipitate (solid) is produced A liquid is produced H 2 O(l) A gas is produced

20 Table F

21 Spontaneous or not? NaCl + AgNO 3 NaNO 3 + AgCl K 2 CO 3 + MgSO 4 K 2 SO 4 + MgCO 3 NH 4 OH + NaNO 3 NaOH + NH 4 NO 3 Yes No

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23 Stoichiometry Goal The role of coefficients in balanced formula equations Mole ratios in a balanced formula Mole-mole stoichiometry problems

24 Stoichiometry Calculations of quantities in chemical reactions

25 Food Example How many pancakes can be made with 8 cups flour, excess eggs and milk? ratio X amount X = 20 pancakes

26 Process for Solving Balance reaction Copy coefficients from reaction into ratio row Place numbers from question in row above ratio row (Setting up proportion) Solve for X using a proportion

27 Food Example How many eggs are needed to make 25 pancakes? ratio X amount X = 5 eggs

28 Chemical Example How many moles of NH 3 can be made with 6 moles H 2 and excess N 2 ? ratio 132 6X amount X = 4 mol NH 3 =

29 Chemical Example How many moles of N 2 are needed to produce 7 moles of NH 3 ? ratio 132 7X amount X = 3.5 mol N 2

30 Chemical Example How many moles of O 2 are needed to produce 9 moles of H 2 O? ratio X amount X = mol O 2 4

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32 Endo/Exothermic Endothermic – Energy is absorbed Energy term is on the left side Exothermic – Energy is released Energy term is on the right side Treat just like a coefficient

33 Example How much energy is produced when 6 moles H 2 reacts with excess N 2 ? ratio 132 6X amount 91.8 X =183.6 kJ


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