CHEMICAL REACTIONS Chapter 7

Changes PHYSICAL CHEMICAL Only affects the size, shape and state. Amount of energy involved in each state varies. CHEMICAL Atoms are rearranged. Bonds broken new substance created Energy released or absorbed

Physical OR Chemical Reactions?

Lab: Conservation of Mass Physical or Chemical Change? A – Dissolving Salt and Water B – Melting Ice C – Lead nitrate mixed with sodium chloride OR sodium iodide D – copper and sulfur E – water and alka-seltzer

Lab: Conservation of Mass Physical or Chemical Change? A – Dissolving Salt and Water B – Melting Ice C – Lead nitrate mixed with sodium chloride OR sodium iodide D – copper and sulfur E – water and alka-seltzer Physical Chemical

Chemical Reactions Rearrange atoms REACTANTS PRODUCTS C2H5OH + 3O2 2CO2 + 3H2O New product atoms and old reactant atoms are not created or destroyed. Mass is always conserved.

Energy and Reactions Energy must be added to break bonds Energy Heat Electricity Sound light

Energy and Reactions Forming bonds releases energy

Energy and Reactions

Examples Exothermic Endothermic Combustion of Methane (Natural Gas). Adding concentrated sulfuric acid to water Acid/Base reactions         Dissolving a strong acid or strong base Endothermic Photosynthesis Dissolving most salts into water (exceptions) Decomposition reactions         A –– > B + C

Diatomic Molecules Most elemental gases do not exist as single atoms H2 N2 F2 O2 I2 Cl2 Br2

7.2 Chemical Reactions Are Represented by Chemical Equations

Chemical Equation A representation in which reactants are written before an arrow and products are written after the arrow.

Reactants Products

Substances that are about to chemically react. Reactants Substances that are about to chemically react.

Substances that are formed from a chemical reaction. Products Substances that are formed from a chemical reaction.

Animation “CO2flask.mov”

Reactants

Carbon,C Reactants

Carbon,C Oxygen, O2 Reactants

Chemical reaction

Products

Carbon Dioxide, CO2 Products

Coefficients Integers used to indicate the ratio by which reactants react and products form.

H2 + O2 H2O Reactants Products

2 H2 + O2 H2O Reactants Products

2 H2 + 1 O2 H2O Reactants Products

2 H2 + 1 O2 2 H2O Reactants Products

2 H2 + O2 2 H2O Reactants Products

2 H2 (g) + O2 (g) 2 H2O (g) Reactants Products

Balancing Chemical Equations

Balancing Guidelines Balance one element at a time. 2) If you incidentally unbalance an element leave it alone. 3) Make successive passes.

Al2O3 + C Al + CO2

Al2O3 + C Al + CO2 (not balanced)

Al2O3 + C Al + CO2

Al2O3 + C Al + CO2 Al Al C Al O C O O O O

Al2O3 + C Al + CO2

2 Al2O3 + C Al + CO2

2 Al2O3 + C Al + CO2 Al Al Al C O C O O O O Al

2 Al2O3 + C Al + CO2

2 2 3 Al2O3 + C Al + CO2

2 2 3 Al2O3 + C Al + CO2 O C O Al Al Al O O O C O C O Al O C O Al Al O

2 2 3 Al2O3 + C Al + CO2

2 3 2 3 Al2O3 + C Al + CO2

2 3 2 3 Al2O3 + C Al + CO2 C O C O Al Al Al O O O C O C O Al C O C O

Balanced 2 3 4 3 Al2O3 + C Al + CO2 C O C O Al Al Al O O O C O C O Al

Balanced 2 3 4 3 Al2O3 + C Al + CO2

not balanced Na2SO3 + S8 Na2S2O3

Na2SO3 + S8 Na2S2O3

1 Na2SO3 1 + S8 Na2S2O3

1 Na2SO3 1 + S1 Na2S2O3

1 Na2SO3 1 + S8 Na2S2O3

1 1 Na2SO3 1 + S8 Na2S2O3 8

1 1 Na2SO3 1 + S8 Na2S2O3 8 S S S S S S S S

1 1 Na2SO3 1 + S8 Na2S2O3 8 S S S S S S S S

1 1 Na2SO3 1 + S8 Na2S2O3 8 S S S S S S S S

1 1 Na2SO3 1 + S8 Na2S2O3 8 S S S S S S S S

1 1 Na2SO3 1 + S8 Na2S2O3 8

1 1 Na2SO3 1 + S8 Na2S2O3 8

1 8 1 Na2SO3 S8 1 + Na2S2O3 8

1 8 x 8 8 8 Na2SO3 + S8 Na2S2O3

1 8 x = 1 8 8 8 Na2SO3 + S8 Na2S2O3

8 1 8 Na2SO3 + S8 Na2S2O3

Balanced 8 1 8 Na2SO3 + S8 Na2S2O3

7.1 Chemical Reactions Are Represented by Chemical Equations

7.2 Chemists Use Relative Masses to Count Atoms and Molecules

TYPES OF REACTIONS Chapter 7

Types of Reaction Fe + O2 Fe2O3 1. Addition Reactions (aka synthesis) A + B AB 2 or more substances combine to form a new compound. small molecules join to form chains - polymerization Fe + O2 Fe2O3

Types of Reactions 2 H2O 2 H2 + O2 2. Decomposition Reactions AB A + B compounds are broken apart into smaller substances Example: Electrolysis of water 2 H2O 2 H2 + O2

Types of Reactions Single – Displacement Reaction AX + B BX + A One element replaces a similar element in a compound Aka Single – Replacement Reaction

Types of Reactions Double – Displacement Reaction AB + CD AD + CB Aka double –replacement reactions Ions from 2 compounds in solution exchange places to produce 2 new compounds. One of the compounds is usually … A precipitate A gas that bubbles off A molecular compound like water

Types of Reactions Combustion Reactions These use O2 as a reactant One product contains O and the other usually H2O Carbon cpd. + O2 CO2 + H2O ___________________________________________________________________________________________________________________

Importance of Good Air Supply Types of Reactions Combustion Reactions These use O2 as a reactant One product contains O , usually H2O ____________________________________________________________________________________________________________________________ Importance of Good Air Supply 2CH4 + 4O2 2CO2 + 4H2O 2CH4 + 3O2 2CO + 4H2O 2CH4 + 2O2 2C + 4H2O

Chapter 7.1 Energy in Reactions

Examples Exothermic Endothermic Combustion of Methane (Natural Gas). Adding concentrated sulfuric acid to water Acid/Base reactions         Dissolving a strong acid or strong base Endothermic Melting of ice evaporation of water boiling of water. Photosynthesis Dissolving most salts into water (exceptions) Decomposition reactions         AB –– > A + B

Other Terms - refers to the ease in which the reactions occurs Exergonic Most cases: are exothermic Bioluminescence Respiration Endergonic Most cases: are endothermic Photosynthesis

Endothermic Reaction (ex. Photosynthesis) – takes in energy- cold pack Exothermic Reactions (ex. Cell Respiration) – gives off energy– hot pack Plus more balancing reactions to show conservation of mass and energy

__Cu+__O2__CuO __Cu+__S__CuS H2O  2H2 + O2 CuCl2 + Zn  ZnCl2 + Cu              860 × 691 - fphoto.photoshelter.com 605 × 500 - fphoto.com __Cu+__O2__CuO __Cu+__S__CuS H2O  2H2 + O2 CuCl2 + Zn  ZnCl2 + Cu HCl + NaOH  HOH + NaCl PbNO3 + KI  PbI + KNO3 PbNO3+NaClPbCl +NaNO3 4CH3 + 7O2 4CO2 + 6H2O

2Cu+O22CuO or Cu+SCuS __H2O  __H2 + __O2 CuCl2 + Zn  ZnCl2 + Cu              448 × 420 - witcombe.sbc.edu 2Cu+O22CuO or Cu+SCuS __H2O  __H2 + __O2 CuCl2 + Zn  ZnCl2 + Cu HCl + NaOH  HOH + NaCl PbNO3 + KI  PbI + KNO3 PbNO3+NaClPbCl +NaNO3 4CH3 + 7O2 4CO2 + 6H2O

__CuCl2 + __Zn  __ZnCl2 + __Cu 2Cu+O22CuO or Cu+SCuS 2H2O  2H2 + O2 __CuCl2 + __Zn  __ZnCl2 + __Cu HCl + NaOH  HOH + NaCl PbNO3 + KI  PbI + KNO3 PbNO3+NaClPbCl +NaNO3 4CH3 + 7O2 4CO2 + 6H2O

4CH3 + 7O2 4CO2 + 6H2O 2Cu+O22CuO or Cu+SCuS 2H2O  2H2 + O2 CuCl2 + Zn  ZnCl2 + Cu __HCl + __NaOH  __HOH + __NaCl __PbNO3 + __KI  __PbI + __KNO3 __PbNO3+__NaCl__PbCl +__NaNO3 4CH3 + 7O2 4CO2 + 6H2O

2Cu+O22CuO or Cu+SCuS 2H2O  2H2 + O2 CuCl2 + Zn  ZnCl2 + Cu HCl + NaOH  HOH + NaCl PbNO3 + KI  PbI + KNO3 PbNO3+NaClPbCl +NaNO3 __CH4 + __O2 __CO2 + __H2O

Examples Exothermic Endothermic Combustion of Methane (Natural Gas). Adding concentrated sulfuric acid to water Acid/Base reactions         Dissolving a strong acid or strong base Endothermic Melting of ice evaporation of water boiling of water. Photosynthesis Dissolving most salts into water (exceptions) Decomposition reactions         A –– > B + C