Chemical Reactions (Chapter 13) coefficients reactantsproducts

Student Learning Objectives Utilize chemical equations to determine the amounts of reactants, products, and energy change. Characterize acids and bases. Describe reactions involving oxygen.

How is a chemical equation balanced?  A chemical reaction is the process of forming new substances.  Atoms are combined to form molecules.  Molecules separate into atoms.  The chemical equation shows definite proportions of each substance. (same numbers of atoms on each side) Al + Br 2  Al 2 Br 6

Practice 1) Pb + PbO 2 + H 2 SO 4  PbSO 4 + H 2 O 2) C 3 H 8 + O 2  CO 2 + H 2 O 3) Al + HCL  AlCl 3 + H 2 4) BaO + H 2 O  Ba(OH) 2

 There are always x atoms or molecules in 1 mole of a substance. Avogadro’s Number Hydrogen & Water x particles mole

Practice 1)Calculate the amount of grams and number of particles in one mole. a) Gold b) NaCl c) Cu(NO 3 ) 2 2)Calculate the number of moles, and the number of molecules, in 2 grams of carbon dioxide.

More Practice 3)How many grams of each reactant are needed and how many grams of product are produced in the reaction? Al + Br 2  Al 2 Br 3

What are exothermic and endothermic reactions?  The amount of chemical potential energy may change during a chemical reaction. Exothermic Reaction Endothermic Reaction Energy releasedEnergy absorbed Reactants → higher PEProducts → higher PE

Activation Energy  A spike of energy is needed to break existing bonds. H 2 + Cl 2  2HCl

Bond Strength  Bond Energy is the energy required to break 1 mole of bonds. (Same energy released when bond forms)  The net bond energy indicates whether the process was exothermic or endothermic. Bond Energy to Break = Bond Energy Released

Examples 1)N 2 + H 2  N 2 H 4 2)H 4 C 2 + O 2  CO 2 + H 2 O

What can cause reaction rates to vary? 1.Temperature 2.Concentration 3.Surface area 4.Catalysts What is this?

Catalysts  A catalyst accelerates the reaction.  Provides different pathway  Lowers activation energy  Reappears as a product Progression of Reaction With catalyst

Practice 1)Why are there warnings on some medications not to break, crush, or chew the pill? 2)Why do you think some laundry soaps contain enzymes? 3)Why are photographic prints processed in the dark?

What is an acid? What is a base?  Acids contain H + and H ions, and are substances that donate hydrogen ions.  Bases contain hydroxide (OH − ) ions, or are substances that accept a hydrogen ions. Proton DonorProton Acceptor

Examples 1)Baking soda (NaHCO 3 ) 2)HCl + NaHCO 3  H 2 CO 3 + NaCl

Practice Identify the acid substances and the base substances. CH 3 CO 2 H + H 2 O  CH 3 CO H 3 O +

Strong Acids & Bases  Strong acids and bases completely ionize in water. Some Strong Bases LiOH lithium hydroxide NaOH sodium hydroxide KOH potassium hydroxide Some Strong Acids HNO 3 nitric acid HCl hydrochloric acid H 2 SO 4 sulfuric acid

 The neutralization reaction of an acid and a base produces water and a salt. AcidBaseWaterSalt HCl + NaOH  H2OH2O + NaCl HBr + KOH  H2OH2O + KBr

pH  A substance that has an equal number of acid and base ions is neutral. (pH balanced) pHSolution 1 to 6Acidic 7Neutral 8 to 14Basic

Practice 1) If the water you drink has a pH of 6.8, is it acidic, basic, or neutral? 2) Blood has buffers to help control the natural pH your body needs. The amount of CO 2 in the blood stream can change pH. What do we do naturally that can change the pH of blood?

What is “acid rain”?  Acid Rain is moisture that has a pH of less than 5.  Rain, snow, sleet, or fog  Rainwater normally has a pH of 5.6 to 6.2  Acids may combine with dust (dry deposition)  Water naturally reacts with CO 2 in the atmosphere, forming a weak acid. water + carbon dioxide  carbonic acid (H 2 CO 3 )

Strong Acids in Our Atmosphere  Human-produced exhaust emissions of sulfur and nitrogen oxides form strong acids. sulfates + water  sulfuric acid (H 2 SO 4 ) nitrates + water  nitric acid (HNO 3 )

Location Question Where would you expect a higher level of acidity in the atmosphere, WY or CA? Why? What are the factors?

Image Credit Simon Fraser/Science Photo Library Trees killed by acid rain Czech Republic

What is an oxidation-reduction reaction?  Redox reactions involve a transfer of electrons, and often the addition or subtraction of oxygen.

Redox Reactions  Corrosion is a redox reaction between a metal and oxygen (O 2 ).  Combustion is a redox reaction between a non-metal and oxygen (O 2 ).

Redox Examples  Corrosion is a redox reaction between a metal and oxygen (O 2 ).  Combustion is a redox reaction between a non-metal and oxygen (O 2 ).

Practice 1)Which element is oxidized and which is reduced? a)HgS + O 2  Hg + SO 2 b)SnO 2 + 2C  Sn + 2CO 2 2) Is the iron oxidized or reduced in the formation of rust? 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s)

More Practice 3) Is a combustion reaction, like the combustion of methane, exothermic or endothermic? CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(l)

How do batteries and fuel cells work?  Batteries have 2 diodes; one that is oxidized and one that is reduced.  Acidic solution reacts with metals One metal is reduced (+ end) One metal is oxidized (– end)  Reactions free electrons Battery

Cathode (+) Anode (–) Metal gains e − Metal is reduced Metal loses e − Metal is oxidized Battery

Fuel Cells  A fuel cell uses a membrane to separate the reactants.  Hydrogen gas is oxidized.  Oxygen gas is reduced.  Product is H 2 O vapor.

Practice 1)Where do you store your batteries? Why? 2)What is the difference between a dry cell battery and an alkaline battery? 3)What is the primary difference between a battery and a fuel cell?

Practice Practice: Where do you store your batteries? Why?  A fuel cell uses a membrane to separate the reactants.  Hydrogen gas is oxidized.  Oxygen gas is reduced.  Product is pure water vapor.

What is electrolysis?  Electrolysis is the use of electric current to cause chemical change.  Reverses chemical reactions  Splits compounds Al 2 O 3 + Energy  Al 2 + O 2

What is electrolysis?  Electrolysis is the use of electric current to cause chemical change.  Reverses chemical reactions  Splits compounds Example Example: Al 2 O 3 + Energy  Al 2 + O 2 Question Question: How do you recharge your cell phone battery?

Practice 1)Is electrolysis an exothermic or endothermic process? 2)Describe the chemical process of recharging your mobile phone device. 3)What other devices operate in the same way? 4)Can you think of other examples of electrolysis?