CHAPTER 6Chemical Reactions and Equations

Warm-up

Who can recall what the 4 pictures were on the intro slide for this chapter?

Fire

Test tube with a blue solid substanceTwo flasks (one with a blue liquid and one with a yellow liquid)

Smoke trail

What do all of these things have to do with chapter 6?

They all show signs of a chemical change

Indications of a Chemical Change

Chemical ChangeThe change of one or more substances into new substances by the rearrangement of atoms.

4𝐹𝑒(𝑠 )+3𝑂2 (𝑔)→2𝐹𝑒2𝑂3(𝑠 )

Change in energy

Formation of a Precipitate(two liquids combine and a solid is produced)

Formation of a gas

Change in color

Parts of a Chemical Equation

Reactants

Physical States(solid, liquid, gas or aqueous)

Coefficients

Products

4𝐹𝑒 3 (𝑠)𝑂2(𝑔)(𝑠) 2𝐹𝑒2𝑂3+¿ →

Writing Equations

Word EquationsUsing the names of chemicals to describe chemical reactions

𝑠𝑜𝑙𝑖𝑑𝑠𝑜𝑑𝑖𝑢𝑚+ h𝑐 𝑙𝑜𝑟𝑖𝑛𝑒𝑔𝑎𝑠→ 𝑠𝑜𝑙𝑖𝑑𝑠𝑜𝑑𝑖𝑢𝑚 h𝑐 𝑙𝑜𝑟𝑖𝑑𝑒

Chemical EquationsUsing chemical formulas and numbers to describe chemical reactions

𝑁𝑎( 𝑠)+𝐶𝑙2 (𝑔)→𝑁𝑎𝐶𝑙( 𝑠)Hopefully you noticed that this equation defies the Law of Conservation of Matter. It is not balanced. Once you master writing equations, you will also learn how to balance equations.

Practice ProblemsUse your ion tables

Solid copper + fluorine gas = solid copper (II) fluoride

Re-write the following chemical equation in words

Re-write the following word equation as a chemical equation

aqueous calcium chloride + Aqueous lithium chromate

aqueous lithium chloride

Solid calcium chromate +

Cu(s) + F2(g) CuF2 (s)

+ energy

2𝐻2𝑂(𝑙)+𝒆𝒏𝒆𝒓𝒈𝒚→2𝐻2 (𝑔)+𝑂2 (𝑔)

EnergyWhen chemical reactions take place, energy is either absorbed or released in the process

An endothermic reaction

An exothermic reaction

Warm up

Watch the following video to complete the warm up

http://www.youtube.com/watch?v=R6bBs2D0cpA

Write the following chemical equation for the reaction that occurred in the video:

Aluminum + iodine = aluminum iodide

You should be able to answer the following questions:

What are the reactants?What are the products?What was the indication that a chemical change took place?Was this an endotherm or exothermic reaction?

Physical States of ElementsMetalso Metals are always represented by their symbols from the

periodic table, with no subscripts

o All metals, with the exception of mercury are solid and will have an (s) following their symbols in an equation

Cu(s)

Non-metalso Are often diatomic (Br,I,N,Cl,H,O,F) so they will

have a subscript of 2.o Most of these diatomic elements will be a gas

except iodine (s) and bromine (l)

Cl2(g)

Physical States of Ionic CompoundsIonic Compoundso Their physical state will be

o (aq) = aqueous if they can dissolve in water (soluble)o (s) = solid if they can’t (insoluble)

Use this table to determine the solubility of ionic compounds:

More Practice ProblemsWhat would be the physical states of the following substances if written in a chemical equation?

PbI2 __________ KNO3 ____________

KI __________ Pb(NO3)2 ____________

Write the following equation with physical states:

Lead (II) nitrate combines with potassium iodide to form potassium nitrate and lead (II) iodide.

(s)

(aq)

(aq)

(aq)

Pb(NO3)2(aq) + KI(aq) KNO3(aq) + PbI2(s)

Warm-up

Watch the following video to see what happenshttp://www.youtube.com/watch?v=BhO8kGrc4dg

Write the chemical equation for the reaction:(Use a solubility table to predict the physical states of each compound)

potassium iodide + lead (II) nitrate = potassium nitrate and lead (II) iodide

Did you write the correct physical state for each compound in the reaction?

Balancing Chemical EquationsWhy?To demonstrate the Law of Conservation of Mass which states:

In a chemical reaction mass is neither created or destroyed

Antoine Lavoisier

What must be conserved?The number and type of atoms

2𝑁𝑎(𝑠 )+𝐶𝑙2 (𝑔)→2𝑁𝑎𝐶𝑙(𝑠 )

2 sodium atom + 2 chlorine atoms = 2 sodium atoms + 2 chlorine atoms

How to Balance a Chemical Equationo Make sure that both sides of an equation have an

equal number of each type of atom represented.

o Balance equations by adding coefficients.

o Never mess with subscripts

NaBrMgClMgBrNaCl ________ 22

Na

Cl

Mg

Br

Strategies for Balancing Chemical Equations1. The even/odd combination

Make the subscript of one, the coefficient of the other and vice versa.

Iron (III) oxide Iron + Oxygen

232 3402 OFeFe

322 ______ OAlOAl Practice:

Strategies Continued2. Balance groups as a whole if the elements of the group

are only represented in the group on each side of the equation.

MgOHAlAlOHMg __)(____)(__ 32

Mg

OH

Al

MgKClOKClOMg ______)(__ 424 Practice:

Strategies Continued3. Balancing Hydrocarbon Combustion Reactions

The first step is to add a coefficient to the hydrocarbon so that the total number of hydrogens in the molecule is divisible by four. Then, balance the product side of the equation before finishing up with oxygen.

0____0____ 2225 HCOCH C

H

O

Practice: 0____0____ 22262 HCOHC

Strategies Continued4. Splitting Water

When hydroxide shows up on one side of an equation and water is on the other side, split water into H(OH) to balance out hydroxide.

OHMgSOSOHOHMg 23322 ______)(__

Practice: OHAlBrHBrOHAl 233 ______)(__

Things to Keep in Mind• Again, do not mess with subscripts• In the final solution, the coefficients have to be in the

lowest whole number ratio.

• If at first you don’t succeed, try, try again! Most of the solutions to these problems come from trial and error.

OHOH 222 424 OHOH 222 22

Comprehensive Practice Problem Write the equation Note the physical state of each substance Balance the equation

Potassium chromate combines with lead (II) nitrate to form potassium nitrate and lead (II) chromate

Warm-up

If I put all the reactants of the following equation into the left side of the balance and all of the products into the right side, why would the balance look like this?

Types of Chemical Reactions

• 5 General Types• Synthesis• Decomposition• Single displacement• Double displacement• Combustion

You will need to know how to identify these reactions

Combustion

CxHy + O2 CO2 + H20

SynthesisA + B AB

(Two elements combine to form a compound)

DecompositionAB A + B

(One compound splits to form two compounds)

Types of Chemical Reactions – 5 General Formulas

Always the products of these combustion reactions

Reactions Cont.Single Replacement (Single Displacement)

A + BC AC + B (Metals replace metals and non-metals replace non-

metals)

Double Replacement (Double Displacement)

AB + XY AY + XB (Compounds switch partners)

Practice Problems

Identify the type of reaction

)(2)()(32

)(4)(42)(2

)()(2)(

)(2)(2)(2)(104

)(4)()(342)(

342

2

22

0108132

32)(3

)(

gss

aqaqaq

sgs

lggg

ssaqs

OFeOFe

LiClCaCrOCrOLiCaCl

MgOOMg

HCOOHC

BaSOFeSOFeBa

s

Combustion Decomposition Single replacememt

Synthesis Double Replacement

Warm-up

What type of reaction does the picture represent?

What are the reactants in this reaction?

Which one will run out first?

Equilibrium http://www.youtube.com/watch?v=JsoawKguU6A

• Many reactions can change direction.

• These are called reversible reactions.

• When no net change occurs in the amount of reactants and products, a system is said to be in equilibrium.

• A system in which opposite actions are taking place at the same rate, it is said to be in dynamic equilibrium.

• Products and reactants are forming at the same rate.

• Reactants are never fully used up because they are constantly being formed from products.

Reaction Rate http://www.bing.com/videos/search?q=activation+energy+video&mid=CC5874704F3D6F93469CCC5874704F3D6F93469C&view=detail&FORM=VIRE7

• How fast do reactions reach equilibrium?

• The amount of energy the particles must have when they collide is called the activation energy of that reaction.

• The speed of reaction measures how quickly the reactants disappear or how quickly the products appear.

• The amount of substance changed per unit time is the rate of reaction.

Factors that Affect the Rate of a Reaction

Temperature affects the rate of reaction also.The higher the temperature, the faster the reaction; the lower the

temperature, the slower the reaction.

The amount of substance present in a certain volume is called the concentration of the substance.

• Raising the concentration of a reactant will speed up a reaction because there are more particles per volume

• When one reactant is used up, the reaction will stop• The reactant that is used up first is called the limiting reactant

Factors that Affect the Rate of a Reaction

• Presence of a catalyst speeds up the rate of a reaction without being permanently changed of used up itself.

• A catalyst speeds up the reaction by lowering the activation energy.

• Biological catalysts are called enzymes.

• Reactions that have undesirable products sometimes have to be slowed down.

• A substance that slows down a reaction is called an inhibitor.