Unit 4 -- Chemical Reactions - Lundquist Labs

Chemical Reactions

Unit 4

Chemical Reactions

2

Unit 4.1

Describing Matter

Physical Properties

• Can be observed without changing the substance

Chemical Properties

• Requires the substance react with another compound or energy source

• Caused the atoms to rearrange

The Science of Chemistry

• Chemical changes result in the substance being consumed to produce a new substance

• Known as chemical reactions

• Reactants are what is being used

• Products are what is being produced



• Signs of a chemical change

• Formation of a gas

• Formation of a solid (precipitate)

• Change in temperature

• Change in color

• Production of light

Do p. 14 in the Packet-Physical-

Measured without changing the substance

-Chemical-Measured by reacting with

something

-Intensive –independent of how much you have

-Extensive-Change with the amount of the

substance you have

-Quantitative-A number

-Qualitative-An opinion


• Chemicals can change both physically and chemically• Physical changes don’t change the substance

• Affect the physical properties of a substance • The arrangement, location, and speed of the particles can change

Properties can be:

-Intensive –independent of how

much you have

-Extensive-Change with the amount

of the substance you have

-Quantitative-A number

-Qualitative-An opinion

Ductile –Pulled into

wires

Malleable --Bendable



10

Representing matter

Atoms• simplest unit of matter

• Ex: atoms of Au

11

Representing matter

Molecule• Two or more atoms

• Ex: Water (H2O, O2)

12

Representing matter

Element• One type of atom

• Ex: Water (Ar, O2)

13

Representing matter

Compound• Two or more elements

• Ex: Water (H2O, CO)

Do p. 15

MM.DD.20XXADD A FOOTER15

Balancing Chemical Reactions

The Law of Conservation of Mass

• Matter cannot be created nor destroyed

• What you start with MUST equal what you end with

When obeyed a reaction is said to be “balanced”


• When balancing you may ONLY CHANGE COEFFICIENTS

• Altering subscripts changes the compoundH2O ≠ H2O2


• Ways to balance equations

• Atom inventory

• Pictures

Balancing Chemical ReactionsTips

1. Keep polyatomic ions together

H2SO4 + Ba(NO3)2 � BaSO4 + HNO3

Example 4


2. Save anything elemental for last

CH4 + O2 � CO2 + H2O

Example 5


3. When stuck double EVERYTHING except what is giving you trouble

C2H6 + O2 � CO2 + H2O

Example 6


Memorizemetals + halogens ⇀ MaXb

CH and/or O + O2⇀ CO2(g) + H2O(g)

H2CO3⇀ CO2 + H2O

metal carbonates ⇀ metal OXIDES + CO2 (ex: MgCO3 ⇀ MgO + CO2)

Writing chemical equations

• ALL about nomenclature

• Ionic compounds

• metals + nonmetals

• Uses charges

• Covalent compounds

• nonmetals only

• Prefixes tell you how many

• Watch out for Diatomics

• Br2 I2 N2 Cl2 H2 O2 F2

Sulfur trioxide is produced from the incomplete combustion of fossil fuels. It reacts with atmospheric water vapor to produce hydrogen sulfate, a key component in acid rain. Write the balanced chemical reaction for this process

Writing chemical equations

• “+”

• Reacts with

• Combines with

• And

• “�”

• Produces

• Forms

• Makes

Sulfur trioxide is produced from the incomplete combustion of fossil fuels. It reacts with atmospheric water vapor to produce hydrogen sulfate, a key component in acid rain. Write the balanced chemical reaction for this process

■ “(s)”

– Any shape word

– solid

■ “(l)”

– Liquid

■ “(g)”

– Gas

– vapor

Do p. 16


Net ionic equations

29

Unit 4.2


Describing chemical reactions

Complete balanced equation Complete ionic equation

• gives the overall reaction stoichiometry

• NOT the forms of the reactants & products as they exist in solution

• represents as IONS all reactants & products that are strong electrolytes

�� 3 2 + 2� → ��2 + 2��3

��2+

+ 2 ��31

− + 2 �

++2

− → �� 2

+ 2 �

+ + ��3

−



Net ionic equation Spectator Ions

• includes only those solution components undergoing a change

• Spectator ions are NOT included

• not involved in the reaction process

��2+

+2 −

→ �� 2

��2+

+ 2 ��31

− + 2 �

+ +2

− → ��2

+ 2 �

+ +2 ��3

−


Spectator Ions



Making short work of net ionic equations

1. Cross out the word nitrate any time it appears on the page.

2. Circle any word that implies solid or gas. (powdered, turnings, chunk, vapor, etc.)

3. Cross out any Group 1 metal that you see UNLESS it is associated with a circled solid or gas word.

4. Underline halides then ask yourself if silver, mercury or lead is present—if not you can cross the halide off as well such as with hydrochloric acid. The H+ is the reacting species. (Bring the halide back as a reacting ion IF you need to oxidize something halide-1

⇀ halogen2-.)

5. Circle “burned in air” or “combines with oxygen” or anything that implies combustion and celebrate!

6. Write whatever remains, and predict a product!


Do p. 17 to 21

For 6-17, you can skip the complete

ionic equation

Stoichiometry

35

Unit 4.3

Review

Balancing

• Reactants = products

• Keep practicing

• Tips:

• Save elemental for last

• Keep polyatomics together

• If stuck double everything

Review

Molar Conversions

• 1 mole = 6.022 x 1023 atoms

• All atoms have a different mass

• Molar mass = the mass of 1 mole

• Add up the mass of the elements on the periodic table

• Pay attention to the number of each element

Its like baking

2 Br + Ch⇀ Br2Ch

2 Br = 1 Ch2 Br = 1 Br2Ch1 Ch = 1 Br2Ch

Mole to Mole Ratio

In a balanced equation coefficients:

• Can be read as molecules AND moles

• Can be used as a conversion

Its like baking

2 Br + Ch⇀ Br2Ch

If you wanted to make 173 grilled cheeses how much bread would you

buy? How much cheese?


Do p. 25

Conservation of mass!

• Matter can not be created nor destroyed

• The reason we balance reactions

• If 10 grams react then 10 grams have to be produced

Its like baking

2 Br + Ch⇀ Br2Ch

If you wanted to make 173 grilled cheeses how many pounds of cheese would you have to buy?

Stoichiometry

• Find a way that works for YOU

• Here are the ways I know. If you learn another SHOW ME

• By steps

• Dimensional analysis

• Round-about

• ALL starts with a plan

Dimensional Analysis

• A way of showing units cancelling out

• Uses conversion factors

• REMEMBER mol:mol ratios are conversions

• MM is X g = 1 mol


Do p. 26

Molar Volume of a Gas

• ALL gases have no attractive forces

• VERY spread out

• Mainly empty space

• The volume of a gas is dependent on temperature and pressure

• You can use PV=nRT to find moles of gas

• At STP 1 mol of gas occupies 22.4 L

Volume to volume stoichiometry

• Simply change volume to moles, then back

• Since you will divide, then multiply by 22.4L/mol you could always just multiply by the mole to mole ratio.

Limiting Reagents

• Limit the amount of product that can be produced

• You will often have a finite supply of reagents so 1 will be used up

• Remaining reactants are called EXCESS

ALL STOICHIOMETRY IS DONE BASED ON THE LIMITING REAGENT!



Do p. 27 & 28

Types of chemical reactions

60

Unit 4.4


First year chem

Second year chem (AP Chem)


Three types of chemical reaction

• Precipitation reactions

• RedOx reactions

• Acid – Base Reactions

Precipitation reactions


• Form a precipitate

• An insoluble solid

• Removed an analyzed by gravimetric analysis (filter it, dry it, find it’s mass and subtract from the initial mass).

• YOU MUST KNOW YOUR SOLUBILITY RULES!


Types of Chemical ReactionsAP Chemistry

Acid – Base Reaction

• Acid (HA) -- produce H+ ions• React with carbonates to make CO2(g)

• Base (MOH) – Produce OH- ions • Includes NH3

• Neutralization

HA (aq) + MOH (aq) – MA (aq) + HOH (l)

When mol HA = mol MOH


Based on dissociation

• \

Strong

Complete dissociation:Every hydrogen (H+) separates from the anion (A-

)

The six strong acids: HNO3, H2SO4, HClO4, HCl, HI, & HBr

Why is HClO4 strong, but HClO3 not?

• Oxygen is an “electron hog”

• Pulls electron away from hydrogen

• Makes H very positive and easily attracted to other molecules

Electronegative


• \

Strong

Complete dissociation:Every hydrogen (H+) separates from the anion (A-

) ONLY group I, and II metal hydroxides are strong: Ca(OH)2, KOH

MOH M+

OH-

Excludes Mg, & Be


Weak

Partial dissociation:Few hydrogen (H+) separates from the anion (A-)

EVERYTHING ELSE

neutralization

mol HA = mol A-= mol MA

• When acid = base = salt

• Reaction H++OH-�H2O

(H+)(Ma)(Va) = (OH-)(Mb)(Vb)

• Determines an unknown concentration of acid or base

Titrations

• The gradual mixing of an acid and base to determine the concentration of and unknown

• An indicator changes color at a set [H+]

Indicator Acid base

Phenolphthalein Colorless pink

Methyl Orange Orange Yellow

Methyl blue Blue Yellow

Litmus Pink/red blue


Titration Curves

• Graphing the pH of a solution as acid/base is added

• pH vs vol. added

• Equivalency point

• When the solution is neutralized, mol HA = mol A- = mol MA

• Strong + strong = pH ~7

• Weak + weak = pH ~7

Do p. 29

11/23/202075

RedOx reactions


Reduction

• An atom gains electrons

Oxidation

• An atom looses electrons

RedOxreactions

77

Unit 4.5

Determining oxidation number


• The oxidation number for an atom in its elemental form is always zero, unless it has a charge

• The oxidation number of all Group 1A metals = +1

• The oxidation number of all Group 2A metals = +2

• Oxygen is -2 (unless H2O2 then -1)

• The oxidation number of fluorine (F) is always -1.

• The sum of the oxidation numbers of all atoms (or ions) in a neutral compound = 0; in an ion = charge of the ion

HALF REACTIONS

• To determine which substances are oxidized and reduced, the reaction should be divided into half reactions.

• Balance the half reactions charge with electrons (e-)

2Br- � Br2 +2e-

2e- + Cl2 � 2Cl-

REDUCING/OXIDIZING AGENTS

Reducing agent

• The substance that is oxidized forcing another to be reduced

Oxidizing agent

• The substance that is reduced forcing another to be oxidized

Do p. 30

11/23/202081

• Since these reaction GENERALLY occur in solutions where water is the solvent, we have an infinite supply of HOH

Balancing RedOx reactions

Practice

Practice

Practice

Lab next classTest after that!

11/23/202086

• Make sure you’ve finished your personal progress check

• Lab: Determination of mass and mole relationships in a chemical reaction

• Lab: Determination of the concentration of store bought hydrogen peroxide by redox reaction with permangnate.

Unit 4 -- Chemical Reactions - Lundquist Labs

Documents