Ch6 I

Massimo

Download

Post to :

URL :

Related Presentations :

Add to Flag Embed

Uploaded from authorPOINTLite

Views: 517

Category: Education

Presentation Description

No description available.

Comments

Presentation Transcript

Slide1:

Chapter 6 – Chemical Reactions

Slide2:

Reaction Equations a A + b B  c C + d D Generalized reaction equation: A,B,C,D are compounds a,b,c,d are coefficients reactants products Reactants combine, and form products, in specific proportions. The coefficient given before each reactant/product in the reaction equation indicates the proportion that each substance is consumed/formed. The state of matter of each reactant or product can also be given in the reaction equation: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution  dissolved in water

Slide3:

Reaction Equations The coefficients given for each of the reactants and the products is a fundamental part of the reaction equation: • Chemicals react in specific proportions • The numbers and kinds of atoms that react are exactly the same as are formed Ex: 2 NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g) The above reaction equation indicates that for every two sodium bicarbonate that are decomposed by heating that one sodium carbonate, one water, and one carbon dioxide are formed. The reaction proportions are given on a per atom (molecule/formula unit) basis. heat

Slide4:

Reaction Equations Ex: 2 NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g) heat The chemical reaction equation is balanced. The numbers of each type of atom on either side of the equation are equal: Reactants: Products: NaHCO3 Na2CO3 H2O CO2 2 x Na 2 x Na 2 x H 1 x C 2 x H 1 x C 1 x O 2 x O 2 x C 3 x O 6 x O Total: 2 x Na, 2 x H, 2 x C, 6 x O 2 x Na, 2 x H, 2 x C, 6 x O Law of conservation of mass: Matter is neither created nor destroyed in chemical reactions.

Slide5:

Conservation of Mass Ex: 2 NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g) heat Law of conservation of mass: Matter is neither created nor destroyed in chemical reactions. Reactants: Products: 2 x Na, 2 x H, 2 x C, 6 x O 2 x Na, 2 x H, 2 x C, 6 x O Mass of Reactants: Mass of Products: 2 x 22.99 amu + 2 x 1.01 amu 2 x 22.99 amu + 2 x 1.01 amu + 2 x 12.01 amu + 6 x 16.00 amu + 2 x 12.01 amu + 6 x 16.00 amu = 168.02 amu = 168.02 amu ( or ) 2 x formula weight of NaHCO3 1 x formula weight of Na2CO3 + 1 x molecular weight of H2O + 1 x molecular weight of CO2 = 2 x 84.01 = 1 x 105.99 + 1 x 18.02 + 1 x 44.01 = 168.02 amu = 168.02 amu

Slide6:

Balancing Reaction Equations Step 1: Write an unbalanced equation, using the correct formulas for all reactants and products. Step 2: Add appropriate coefficients to balance the numbers of atoms of each element. Step 3: Check the equation to make sure the numbers and kinds of atoms on both sides of the equation are the same. Step 4: Make sure the coefficients are reduced to their lowest whole-number values.

Slide7:

Balancing Reaction Equations Example: Natural gas (CH4) burns in oxygen to yield water and carbon dioxide (CO2). Write a balanced equation for the reaction. reactants: CH4, O2 products: H2O, CO2 write the unbalanced equation: CH4 + O2  H2O + CO2 2) balance the numbers of each atom type CH4 + O2  2 H2O + CO2 (hydrogen is balanced, but oxygen is not) CH4 + 2 O2  2 H2O + CO2 (balanced equation) 3) check that the numbers of each atom type are equal on both sides of the equation (yes) 4) check that the coefficients do not have a common multiple greater than 1

Slide8:

Mass and reaction proportions The relation between the mass of the reagent and the numbers of (atoms, molecules, or formula units) that are present is indicated by (atomic weight, molecular weight, or formula weight). Atomic weight is the mass (in amu) of 1 atom Molecular weight is the mass (in amu) of 1 molecule Formula weight is the mass (in amu) of 1 formula unit (All of these are subcategories of molar mass.) Molar mass has a dual meaning: Molar mass is the mass (in grams) of 1 mole (mol) of a substance. 1 mol of atoms/molecules/formula units = 6.02 x 1023 atoms/molecules/formula units (Avogadro’s number) ( or ) 6.02 x 1023 amu = 1 gram

Slide9:

Mass and reaction proportions 2 AgNO3 + MgCl2  2 AgCl + Mg(NO3)2 It is very convenient to weigh silver nitrate and magnesium chloride in order to combine them in the correct ratio for the reaction. It is exceedingly difficult to count out the appropriate numbers of atoms! Suppose there are 1.65 g of AgNO3, how much MgCl2 would be required for a complete reaction to occur according to the above equation? First: calculate how many moles of AgNO3 are available (1.65 g) (1 mol) = 9.71 x 10-3 mol AgNO3 (1) (169.9g) Second: factor in the proportion that AgNO3 reacts with MgCl2 (9.71 x 10-3 mol AgNO3) (1 mol MgCl2) = 4.86 x 10-3 mol MgCl2 (1) (2 mol AgNO3) Third: calculate the mass of MgCl2 required (4.86 x 10-3 mol MgCl2) (95.21 g MgCl2) = 0.462 g MgCl2 (1) (1 mol MgCl2)

Slide10:

Mass and reaction proportions The coefficients in a balanced chemical equation tell how many molecules, and thus how many moles, of each reactant are needed and how many molecules, and thus moles, of each product are formed. This information is the stoichiometry of the reaction.

Slide11:

Key Conversions mass  moles (divide by the molar mass) moles  mass (multiply by the molar mass) moles  atoms (multiply by Avogadro’s number) atoms  moles (divide by Avogadro’s number) mass  atoms (divide by molar mass, multiply by Avogadro’s number) atoms  mass (divide by Avogadro’s number, multiply by molar mass) Become familiar with these basic calculations!!! (always keep track of the units)

Slide12:

Molar Mass Molar mass of H2O: 2 x H (1.0079 amu) + 1 x O (15.9994 amu) = 18.0152 amu Molar mass of CaCl2: 1 x Ca (40.08 amu) + 2 x Cl (35.453 amu) = 110.99 amu Molar mass of C10H16ClNO: 10 x C (12.011 amu) + 16 x H (1.0079 amu) + 1 x Cl (35.453 amu) + 1 x N (14.01 amu) + 1 x O (15.9994 amu) = 201.70 amu

Slide13:

Reaction Equations MnO2 + 4 HCl  MnCl2 + Cl2 + 2 H2O How many molecules of chlorine gas are produced when manganese(IV) oxide is combined with hydrochloric acid? What mass of MnO2 is required to produce 13.76 g Cl2 ? molar mass (g/mol): 86.9368 36.461 125.844 70.906 18.0152

Slide14:

Percent Yield During a chemical reaction, there may be reasons that the recovered product is not exactly equal to the amount predicted by the initial amount of reactants. Theoretical yield is the amount of product that should be recovered given some amount of reactants. Actual yield is the amount of product recovered from the reaction. Percent yield = actual yield x 100 theoretical yield AgNO3 + KI  AgI + KNO3 (molar masses AgNO3, AgI = 169.88, 234.773 g/mol) 1.16 g of AgNO3 are combined with KI in equal-molar ratio to produce 0.88 g of AgI. What is the percent yield in the recovery of AgI? (54.9 %)