Introduction to Chemical Reactions

Introduction to Chemical Reactions
Chapter #7 Introduction to Chemical Reactions

Chemical Change Evidence
Chapter 6

What is a clue that a chemical reaction has occurred? a) The color changes. b) A solid forms. c) Bubbles are present. d) A flame is produced. Chapter 6

What is a clue that a chemical reaction has occurred? “Colorless hydrochloric acid is added to a red solution of cobalt(II) nitrate, turning the solution blue.” a) The color changes. b) A solid forms. c) Bubbles are present. d) A flame is produced. Chapter 6

What is a clue that a chemical reaction has occurred? “A solid forms when a solution of sodium dichromate is added to a solution of lead nitrate.” a) A gas forms. b) A solid forms. c) Bubbles are present. d) A flame is produced. Chapter 6

Chemical Reactions A chemical equation is an abbreviated way to show a chemical or physical change A chemical change alters the physical and chemical properties of a substance Factors that indicate a chemical change Change in color Temperature change Change in odor Change in taste (we do not taste chemicals) Reactions always contain an arrow that separates the reactants from the products Reactants Products Chapter 6

Types of Chemical Reactions
Combination reaction (synthesis) Elements for reactants Examples: H2 + O2 H2O N2 + H2 NH3 Al + O2 Al2O3 The Law of Conservation of matter, states matter cannot be created nor destroyed, the means equations must be balanced.

Balance the first equation H2 + O2 H2O Note two oxygen atoms on the reactant side and only one on the product side, therefore place a two in front of water

Balance the first equation H2 + O2 2H2O Note two oxygen atoms on the reactant side and only one on the product side, therefore place a two in front of water The two now doubles everything in water, thus 4 hydrogen and 2 oxygen. Now place a 2 in front of hydrogen.

Balance the first equation 2H2 + O2 2H2O Note two oxygen atoms on the reactant side and only one on the product side, therefore place a two in front of water The two now doubles everything in water, thus 4 hydrogen and 2 oxygen. Now place a 2 in front of hydrogen.

Now balance the second equation N2 + H2 NH3 Note two nigrogen atoms on the reactant side and only one on the product side. Place a 2 in front of ammonia

Now balance the second equation N2 + H2 2NH3 Note two nitrogen atoms on the reactant side and only one on the product side. Place a 2 in front of ammonia. This makes 2 nitrogen atoms and 6 hydrogen atoms. Now place a 3 in front of hydrogen to balance hydrogen atoms.

Now balance the second equation N H2 2NH3 Note two nitrogen atoms on the reactant side and only one on the product side. Place a 2 in front of ammonia. This makes 2 nitrogen atoms and 6 hydrogen atoms. Now place a 3 in front of hydrogen to balance hydrogen atoms.

Decomposition Reaction Compounds form simpler compounds or elements. Examples H2O H O2

Decomposition Reaction Compounds form simpler compounds or elements. Examples 2H2O H O2

Decomposition Reaction Compounds form simpler compounds or elements. Examples 2H2O 2H O2 Notice decomposition reactions are the opposite of combination reactions

Single Replacement reactions have an element and a compound for reactants. Example: Zn + HCl How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound

Single Replacement reactions have an element and a compound for reactants. Example: Zn + HCl ZnCl H Now make the products stable. Slide with Clyde

Single Replacement reactions have an element and a compound for reactants. Example: Zn + HCl ZnCl H2 Now make the products stable. Slide with Clyde

Single Replacement reactions have an element and a compound for reactants. Example: Zn + HCl ZnCl H2 Now make the products stable. Slide with Clyde Now Balance

Single Replacement reactions have an element and a compound for reactants. Example: Zn + 2HCl ZnCl H2 Now make the products stable. Slide with Clyde Now Balance

Single Replacement reactions have an element and a compound for reactants. Another Example: Cl2 + MgBr2 How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound. In this case we are trading nonmetals

Single Replacement reactions have an element and a compound for reactants. Another Example: Cl2 + MgBr2 Br MgCl How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound. In this case we are trading nonmetals

Single Replacement reactions have an element and a compound for reactants. Another Example: Cl2 + MgBr2 Br MgCl2 How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound. In this case we are trading nonmetals

Double Replacement reactions contain compounds as reactants. HCl + Ca(OH)2 CaCl HOH Check formulas, and slide with Clyde when necessary

Double Replacement reactions contain compounds as reactants. 2HCl + Ca(OH)2 CaCl HOH Check formulas, and slide with Clyde when necessary Now Balance!

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. H2 + O2 CH4 + O2 What is the oxide of hydrogen?

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. H2 + O2 CH4 + O2 What is the oxide of hydrogen? Water

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. H2 + O2 H2O CH4 + O2 What is the oxide of hydrogen? Water And the oxide of carbon?

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. H2 + O2 H2O CH4 + O2 CO H2O What is the oxide of hydrogen? Water And the oxide of carbon? Carbon dioxide

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. 2H2 + O2 2H2O CH4 + O2 CO2 + H2O Now balance

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. 2H2 + O2 2H2O CH4 + O2 CO H2O Now balance

Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element. 2H2 + O2 2H2O CH O2 CO H2O Now balance

REDOX reactions where the oxidation number changes from reactants to products. Oxidation is when the oxidation number increases, by losing of electrons. Reduction is when the oxidation number decreases by gaining electrons. Consider the following equation: H2 + O2 H2O What are the oxidation numbers of hydrogen and oxygen?

REDOX REACTIONS H2 + O2 H2O How about hydrogen and oxygen in water?
2(1+) 2- = 0 H2 + O2 H2O How about hydrogen and oxygen in water?

REDOX REACTIONS H2 + O2 H2O How about hydrogen and oxygen in water?
2(1+) 2- = 0 H2 + O2 H2O How about hydrogen and oxygen in water? Oxidation is caused by the oxygen molecule, so it is referred to as the oxidizing agent (OA) Reduction is caused by the hydrogen molecule, so it is referred to as the reducing agent (RA) reduced oxidized

REDOX REACTIONS Note: All of the previously discussed reactions are REDOX except the double replacement reactions. The number of electrons lost is equal to the number of electrons gained in a reaction. Why? Most elements have variable oxidation numbers, except for hydrogen, oxygen, and the memorized polyatomic ions.

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H+ and oxygen is 2- 1+ 4(2-)=0

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H is 1+ and oxygen is 2- 1+ 7+ 4(2-)=0

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H is 1+ and oxygen is 2- 1+ 7+ 4(2-)=0 5+

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H is 1+ and oxygen is 2- 1+ 7+ 4(2-)=0 5+ 3+

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H is 1+ and oxygen is 2- 1+ 7+ 4(2-)=0 5+ 3+ 1+

REDOX REACTIONS Oxidation numbers for a compound must add up to equal zero, while the oxidation numbers for a polyatomic ion must up to equal the charge of that ion. Consider the following chlorine compounds HClO4, HClO3, HClO2, HClO, Cl2, HCl What is the oxidation number of chlorine in each of these compounds, assuming H is 1+ and oxygen is 2- 1+ 7+ 4(2-)=0 5+ 3+ 1+ 1-

REDOX REACTIONS 3(2-)=2- How about sulfur in SO3 2-

REDOX REACTIONS How about sulfur in SO3 2- How about carbon in C6H12O6
4+ 3(2-)=2- How about sulfur in SO3 2- How about carbon in C6H12O6 12(1+) +6(2-)=0

REDOX REACTIONS How about sulfur in SO3 2- How about carbon in C6H12O6
4+ 3(2-)=2- How about sulfur in SO3 2- How about carbon in C6H12O6 0 + 12(1+) +6(2-)=0

Aqueous Ionic Compounds
Most ionic compounds dissolve in water to produce solutions that conduct electricity. The degree to which a solution will conduct electricity is used to determine if a solute is a strong or weak electrolyte. Solutions that do not conduct electricity are called nonelectrolytes. Molecular compounds that dissolve in water to conduct electricity, are acids or bases. Strong acids/bases are referred to as strong electrolytes since they are good conductors of electricity. Weak acid solutions do not conduct electricity well and are called weak electrolytes

Most ionic compounds dissolve in water to produce solutions that conduct electricity. The degree to which a solution will conduct electricity is used to determine if a solute is a strong or weak electrolyte. Solutions that do not conduct electricity are called nonelectrolytes. Molecular compounds that dissolve in water to conduct electricity, are acids or bases. Strong acids/bases are referred to as strong electrolytes since there solutions are good conductors of electricity. Weak acid/base solutions do not conduct electricity well and are called weak electrolytes. How do we tell if a solution conducts electricity?

Strong electrolyte Weak electrolyte Nonelectrolyte

Solutions are homogeneous mixtures of a solute and a solvent. The solute is the solution component in the smallest amount while the solvent is the larger component of a solution. Solutes whose solutions conduct electricity are called electrolytes Solutes whose solutions do not conduct electricity are called nonelectrolytes Electrolytes are solutes that form ions when they dissolve. Ionic solutes or acids usually form solutions that conduct electricity.

There are some more specific rules that allows us to better estimate the solubility of ionic compounds. You will be given these if you need them.

Precipitation Reactions
Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(?) + AgNO3(?) AgCl(?) + NaNO3(?)

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(?) AgCl(?) + NaNO3(?)

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(aq) AgCl(?) + NaNO3(?)

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(?)

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) This is called a formula equation

Using the solubility rules on the previous slide asign (s) and (aq) to the formulas for the following equation NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) This is called a formula equation When Ionic solids and acids dissolve in water ions are formed, and the aqueous formulas really do not exist. A more realistic equation would be the ionic equation.

NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) formula equation Separating the aqueous substances into ions produces an ionic equation. Na+(aq) + Cl-(aq) + Ag+(aq) AgCl(s) + Na+(aq) + NO3- (aq) ionic equation

NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) formula equation Separating the aqueous substances into ions produces an ionic equation. Na+(aq)+Cl-(aq)+Ag+(aq)+NO3-(aq) AgCl(s)+Na+(aq)+NO3-(aq) ionic equation Substances found on both sides of the equation are called spectator ions and are boxed above. Eliminating the spectator ions generates the net ionic equation. Ag+ (aq) + Cl- (aq) AgCl (s) Net ionic equation

It is possible for all of the reactants and products to be water soluble and thus produce all spectator ions. If this is the case then all of the ions cancel out and there is no net ionic equation. When this occurs then we say that there is No Reaction, and give the label NR.

Five Driving Forces Favor Chemical Change Formation of a solid (Precipitate formation) Formation of water (acid base reactions) Transfer of electrons (REDOX) reaction Formation of a gas (many different types) Formation of a weak electrolyte (formation weak acids and bases)

Formation of water is a normal product between acids and bases. Since acids and bases dissolve in water to make solutions that are electrolytes, then we conclude that acids and bases have some ionic character. Since water does not ionize, then when water is formed, we will also have a net ionic equation and then a chemical reaction.

Strong acids and bases ionize 100%! Memorized Strong acids and bases: Bases Acids HCl (aq) HI (aq) HBr (aq) HNO3 H2SO4 HClO4 Hydroxides of group I and II metals, except Be and Mg

Aqueous Reactions Acids undergo characteristic double replacement reactions with oxides, hydroxides, carbonates and bicarbonates. 2HCl (aq) CuO (s)  CuCl2 (aq) H2O (l) 2HCl (aq) Ca(OH)2 (aq)  CaCl2 (aq) H2O (l) 2HCl (aq) CaCO3 (aq)  CaCl2 (aq) H2O (l) CO2 (g) 2HC l (aq) + Sr(HCO3)2 (aq)  SrCl2 (aq) + 2H2O (l) CO2 (g)

Acid/Base Gas Evolution
Acids undergo characteristic double replacement reactions with oxides, hydroxides, carbonates and bicarbonates. 2HCl (aq) + CuO (s)  CuCl2 (aq) + H2O (l) 2HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + 2H2O (l) 2HCl(aq) +CaCO3(aq) CaCl2 (aq)+H2O (l) +CO2 (g) 2HC l(aq)+Sr(HCO3)2(aq)SrCl2 (aq)+2H2O(l)+ 2CO2 (g)

Bases undergo a double replacement reaction with acids called neutralization: NaOH (aq) HCl (aq)  H2O (l) NaC l (aq) In words this well known reaction is often described as: “acid plus base = salt plus water” We previously discussed this reaction when describing types of reactions.

We have discussed the double replacement reactions and ionic equations before. Since the acids and bases undergo double replacement reactions called neutralization reactions, then they can have ionic equations too. Formula equation: HCl (aq) NaOH (aq)  NaCl (aq) H2O (l) Total ionic equation: H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq)  Na+ (aq) + Cl- (aq) + H2O (l) Net ionic equation: H+ (aq) OH- (aq)  H2O (l)

Another property of acids is their reaction with certain metals to produce hydrogen gas, H2 (g). Zn (s) HC l (aq)  H2 (g) ZnCl2 (aq) This is an example of a single replacement reaction and is a redox reaction. Total ionic equation: Zn (s) H+ (aq) Cl- (aq)  H2 (g) Zn2+ (aq) Cl- (aq) Net ionic equation: Zn (s) H+ (aq)  H2 (g) Zn2+ (aq)

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Introduction to Chemical Reactions

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