Honors Chemistry

All chemical reactions have two parts:

Reactants - the substances you start with

Products- the substances you end up with

The reactants turn into the products.

Reactants Products

In a chemical reaction The way atoms are joined is changed Atoms aren’t created of destroyed. Can be described several ways:1. In a sentence

Copper reacts with chlorine to form copper (II) chloride.

2. In a word equationCopper + chlorine copper (II) chloride

Symbols in equations the arrow separates the

reactants from the products Read “reacts to form” The plus sign = “and” (s) after the formula = solid (g) after the formula = gas (l) after the formula = liquid

Symbols used in equations (aq) after the formula -

dissolved in water, an aqueous solution.

used after a product indicates a gas (same as (g))

used after a product indicates a solid (same as (s))

Symbols used in equations indicates a reversible

reaction

shows that heat is supplied to the reaction

is used to indicate a catalyst is supplied, in this case, platinum.

heat ,

Pt

What is a catalyst?

A substance that speeds up a reaction, without being changed or used up by the reaction.

Enzymes are biological or protein catalysts.

Skeleton Equation

Uses formulas and symbols to describe a reaction

doesn’t indicate how many. All chemical equations are

sentences that describe reactions.

Convert these to equations Solid iron (III) sulfide reacts with

gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.

Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

Now, read these:

Fe(s) + O2(g) Fe2O3(s)

Cu(s) + AgNO3(aq)

Ag(s) + Cu(NO3)2(aq)

NO2 (g) N2(g) + O2(g)

Pt

Balanced Equation

Atoms can’t be created or destroyed

All the atoms we start with we must end up with

A balanced equation has the same number of each element on both sides of the equation.

Rules for balancing:

Assemble, write the correct formulas for all the reactants and products

Count the number of atoms of each type appearing on both sides

Balance the elements one at a time by adding coefficients (the numbers in front) - save H and O until LAST!

Check to make sure it is balanced.

Never change a subscript to balance an equation. If you change the formula you are describing a

different reaction.

H2O is a different compound than H2O2

Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.

Example

H2 + H2OO2

Need twice as much O in the product

R PH

O

2

2

2

1

Example

H2 + H2OO2

Changes the O

R PH

O

2

2

2

1

2

Example

H2 + H2OO2

Also changes the H

R PH

O

2

2

2

1

2

2

Example

H2 + H2OO2

Need twice as much H in the reactant

R PH

O

2

2

2

1

2

2

4

Example

H2 + H2OO2

Recount

R PH

O

2

2

2

1

2

2

4

2

Example

H2 + H2OO2

The equation is balanced, has the same number of each kind of atom on both sides

R PH

O

2

2

2

1

2

2

4

2

4

Example

H2 + H2OO2

This is the answer

R PH

O

2

2

2

1

2

2

4

2

4

Not this

Balancing Examples

_AgNO3 + _Cu _Cu(NO3)2 + _Ag

_Mg + _N2 _Mg3N2

_P + _O2 _P4O10

_Na + _H2O _H2 + _NaOH

_CH4 + _O2 _CO2 + _H2O

Balancing Examples

2AgNO3 + Cu Cu(NO3)2 + 2Ag

3Mg +N2 Mg3N2

4P + 5O2 P4O10

2Na + 2H2O H2 + 2NaOH

CH4 + 2O2 CO2 + 2H2O

Types of Reactions

There are millions of reactions. Can’t remember them all Fall into several categories. We will learn 5 major types. Will be able to predict the products. For some, we will be able to predict

whether they will happen at all. Will recognize them by the reactants

COMBINATION REACTIONCOMBINATION REACTION

A reaction in which two or more substances combine to form a single product.

A +B + CA +B + C ABC ABCCaO(s) + SOCaO(s) + SO22(g) (g) CaSO CaSO33(s)(s)

Write and balance

Ca + Cl2 Fe + O2 Al + O2 Remember that the first step

is to write the correct formulas Then balance by using

coefficients only

DECOMPOSITION REACTIONDECOMPOSITION REACTIONA reaction in which a single compound

reacts to give two or more substances, usually requiring a raise in temperature.

ABCABC A + B + C A + B + C

2KClO2KClO33(s) (s) 2KCl(s) + 3O 2KCl(s) + 3O22(g)(g)

#2 - Decomposition Reactions decompose = fall apart one reactant falls apart into two

or more elements or compounds.

NaCl Na + Cl2

CaCO3 CaO + CO2

Note that energy is usually required to decompose

electricity

#2 - Decomposition Reactions Can predict the products if it is

a binary compound Made up of only two elements Falls apart into its elements H2O HgO

electricity

Fig. 8-13, p. 215

2H2O(l) →

•Can predict the products if it is a binary compound •Made up of only two elements•Falls apart into its elements

#2 - Decomposition Reactions If the compound has more

than two elements you must be familiar with page 10 of your packet

NiCO3

KClO3(aq)

pp. 218, 220

Single Displacement (or Replacement) Reactions

Fig. 8-15, p. 218

Single Displacement (or Replacement) Reactions

PREDICT THE PRODUCT

1. Ca + HCl

2. ZnBr2 + I2

3. Cu + AgNO3

Answers are on the next slide.

#3 Single Replacement Metals replace other metals (and

hydrogen) K + AlN Zn + HCl Think of water as HOH Metals replace one of the H,

combine with hydroxide. Na + HOH

We can tell whether a reaction will happen

Some chemicals are more “active” than others

More active replaces less active

There is a list on page 11 - called the Activity Series of Metals

Higher on the list replaces lower.

#3 Single Replacement Note the * concerning Hydrogen H can be replaced in acids by everything

higher Li, K, Ba, Ca, & Na replace H from acids

and water Fe + CuSO4

Pb + KCl Al + HCl

#3 - Single Replacement What does it mean that Hg and Ag are

on the bottom of the list? Nonmetals can replace other

nonmetals Limited to F2 , Cl2 , Br2 , I2 (halogens) Higher replaces lower. F2 + HCl

Br2 + KCl

pp. 220, 223

Double Displacement (or Replacement) Reactions

Double Displacement (or Replacement) Reactions

PREDICT THE PRODUCT & BALANCE

1. MgSO4 + LiOH ___________

2. Pb(NO3)2 + Na2CO3 ____________

3. HNO3 + Ba(OH)2 ___________

Answers are on the next slide.

Double Displacement (or Replacement) Reactions

ANSWERS1. MgSO4 + 2 LiOH Mg(OH)2 + Li2SO4

2. Pb(NO3)2 + Na2CO3 PbCO3 + 2 NaNO3

3. 2 HNO3 + Ba(OH)2 Ba(NO3)2 + 2 H2O

Exchange cations

Double Replacement Two things replace each other. Reactants must be two ionic compounds or

acids. Usually in aqueous solution NaOH + FeCl3

The positive ions change place.

NaOH + FeCl3 Fe+3 OH- + Na+1 Cl-1

NaOH + FeCl3 Fe(OH)3 + NaCl

Double Replacement

Has certain “driving forces” Will only happen if one of the products: doesn’t dissolve in water and forms a

solid (a “precipitate”), or is a gas that bubbles out, or is a covalent compound (usually water).

Oxidation and Reduction Reactions

Early chemists saw oxidation as the combination of a material with oxygen

Today, many of these reactions may not even involve oxygen

Redox currently says that electrons are transferred between reactants

Always occur simultaneously. Called redox reactions.

Oxidation and Reduction Reactions

Oxidation – refers to a loss of electrons, or gain of oxygen

Reduction – refers to a gain of electrons, or loss of oxygen

Oxidizing agent – the substance being reduced

Reducing agent – the substance being oxidized

Oxidation and Reduction Reactions Loss of Electrons is Oxidation Gain of Electrons is Reduction

LEO SAYS GER

Rules For Assigning Oxidation States

Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom

Balancing Redox Reactions If the oxidation number changes, that

element has undergone oxidation or reduction

Reaction as a whole must be redox Half-reaction – equation showing just

the oxidation or just the reduction

Balancing Redox Reactions (in an acid)

+4 -2 +7 -2 +6 -2 +2

SO2 + MnO4- →SO4

2- + Mn2+

Divide the equation into half-reactions.

SO2 → SO42- MnO4

- → Mn2+

Oxidation Reduction

Balance all atoms except O and H

Balancing Redox Equations

Balance O by adding H2O.

2H2O + SO2 →SO42- MnO4

- →Mn2+ + 4H2O

Balance H by adding H+.

2H2O + SO2 → SO42- + 4H+

8H+ + MnO4- → Mn2+ + 4H2O

Balance net charge by adding e-.

2H2O + SO2 →SO42- + 4H+ + 2e-

5e- + 8H+ + MnO4- →Mn2+ + 4H2O Step 6.

Make e- gain equal e- loss; then add half-reactions.

5(2H2O + SO2 →SO42- + 4H+ + 2e-)

2(5e- + 8H+ + MnO4- →Mn2+ + 4H2O)

______________________________________10H2O + 5SO2 + 10e- + 16H+ + 2MnO4

- →2Mn2+ + 8H2O + 5SO4

2- + 20H+ + 10e-

Cancel anything that's the same on both sides.

2H2O + 5SO2 +2MnO4- →2Mn2+ +

5SO42- + 4H+

Balancing Redox Reactions (in a base)

Follow steps 1 – 7 then:

8. Identify the number of proton (H+) in the acidic answer. Add the same number of OH+ ions to BOTH sides of the equation.

9. If H+ and OH+ appear on the same side of the equation, they will react in a 1:1 ratio to form H2O.

10. Cancel out water molecules that appear on both sides of the equation.

11. Check that all is balanced

PRECIPITATION REACTIONPRECIPITATION REACTION

A reaction where an insoluble solid is formed during a reaction between two aqueous solutions.

(aq) (aq) + + (aq)(aq) (aq)(aq) + + (s)(s)2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) +

PbI2(s)Exchange Exchange cationscations

Ionic Equations Many reactions occur in water- that is, in

aqueous solution Many ionic compounds “dissociate”, or separate,

into cations and anions when dissolved in water AgNO3 + NaCl AgCl + NaNO3

1. this is the full equation2. Write it as an ionic equation3. Eliminating ions not directly involved

(spectator ions) = net ionic equation

Molecular, Ionic, Net Ionic Equations

How Do We Predict Solubility?

NEUTRALIZATION REACTIONNEUTRALIZATION REACTION

A reaction between an acid and a base which results in the production of a salt and water.

HA + BOH (metal/nonmetal) + H2O

HNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)

COMBUSTION REACTIONCOMBUSTION REACTION Means “add oxygen” A compound composed of only C, H, and

maybe O is reacted with oxygen If the combustion is complete, the products

will be CO2 and H2O.

If the combustion is incomplete, the products will be CO (possibly just C) and H2O.

A reaction of a substance with oxygen, usually the rapid release of heat produces a flame.

CH + OCH + O22 CO CO22 + H + H22OO

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)

Combustion Many times in a combustion reaction,

heat energy is given off. In chemical terms this is called an exothermic reaction.

Thermochemistry is field of chemistry which studies the transfer of heat in a reaction.

The thermodynamic equation representing this exothermic reaction is:

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) + heat (in Joules)

Examples

C4H10 + O2 (assume complete)

C4H10 + O2 (incomplete)

C6H12O6 + O2 (complete)

C8H8 +O2 (incomplete)

GAS FORMATION REACTIONSGAS FORMATION REACTIONS A reaction that produces a gas from reactants not

in the gaseous state.

2 HCl (aq) + ZnS (s) ZnCl2 (aq) + H2S (g)

Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)

Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance.

NaNa22COCO33 + 2HCl + 2HCl 2 NaCl + H 2 NaCl + H22COCO33

HH22COCO3 3 CO CO22 + H + H22OO

Besides carbonic acid (H2CO3), sulfurous acid (H2SO3) also decomposes into SO2 and water.

COMMON GAS FORMATION REACTIONS COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBERYOU SHOULD REMEMBER

NH4OH → NH3 (g) + H2O (l)

H2CO3 → CO2 (g) + H2O (l)

H2SO3 → SO2 (g) + H2O (l)

Remember an equation...

Describes a reaction Must be balanced in order to follow

the Law of Conservation of Mass Can only be balanced by changing

the coefficients. Has special symbols to indicate

physical state, and if a catalyst or energy is required.

Table 8-3, p. 223

Examples

H2 + O2

H2O Zn + H2SO4 HgO KBr +Cl2

AgNO3 + NaCl

Mg(OH)2 + H2SO3