Chapter 7Chapter 7Chapter 7Chapter 7

Chemical ReactionsChemical Reactions

7-1 Describing Reactions

• In a chemical __________, the substances that undergo change are called ___________

• The new substances formed as a result of that change are called ___________

• _________ ____________• Ex. Carbon + oxygen carbon dioxide• ________ equation

Chemical equations• Ex. C + O2 CO2

• Chemical _________• A chemical __________ is a

representation of a chemical reaction in which the reactants and products are expressed as ____________

Conservation of Mass• During chemical reactions, the________

of the products is always_______ to the mass of the reactants.

• Established by Antoine Lavoisier and is known as the_____________________

• The law of conservation of mass states that mass is neither _________ nor __________ in a chemical reaction

How is mass conserved in chemical change?

Activity• Follow the directions on page 191 in

your book• Fill out following information• Mass of the bag and the water=____________• Mass of a square piece of paper with sides

10cm__________________• Mass of the tablet and the paper together____________• Mass of just the tablet_______________• The combined masses of the bag, the water, and the

tablet___________• Mass of the bag and its contents_____________

Activity questions1. How do you know whether a

chemical change took place?

Activity Question• What happened to the mass of the

plastic bag and its contents after the bubbling stopped?

• What might this information tell you about a chemical change?

Balancing Equations7-1 Continued

• In order to show that mass is conserved during a reaction, a chemical equation must be _________

• You can balance a chemical equation by changing the_________, the numbers that appear _________ the formulas

• As you balance equations, you should never change the ___________ in a formula

Steps to balancing equations

1. Count the _________ of atoms of each element on each side of the equation

2. Ex: N2H4 + O2 N2 + H2O3. Left side has ____ nitrogen,____hydrogen,

and ______ oxygen atoms4. The right side has

____nitrogen,_____hydrogen, and____oxygen atom

5. The hydrogen and oxygen atoms need to be_______.

Steps to balancing equations

6. Change one or more coefficients until the equation is balanced

_1_N2H4 + _1_O2 _1_N2 + _2_H2O

• The equation is now balanced• Each side has _____ nitrogen,_____

oxygen, and _______ hydrogen atoms

Practice Balancing equations problems

1. ___Na + ___H2O ____NaOH + ___H2

2. ___HCl + ___CaCO3 ____CaCl2 +___CO2 + ____H2O

3. ____Al + ____Cl2 _____AlCl3

4. ___Cu + _____O2 _____CuO

5. ____H2O2 ____H2O + ____O2

What is a MOLE?It is a number of things….. - Just like a dozen

1 dozen eggs = 12 eggs

So, instead of 12 the mole is equal to 602 billion trillion

– OR-

6.02 x 1023

602 000 000 000 000 000 000 000

Just How Big is a Mole?6.02 X1023

 Pennies:

Would make at least 7 stacks that would reach the moon.

How Big is a mole?Cover the earth to a depth of 200 miles

with soft drink cans.

Cover the USA to a depth of 9

miles of unpopped popcorn kernels.

The mole is many things….

1 dozen cookies = 12 cookies1 mole of cookies = 6.02 x 1023 cookies

1 dozen cars = 12 cars 1 mole of cars = 6.02 x 1023

cars

1 dozen Al atoms = 12 Al atoms1 mole of Al atoms = 6.02 x 1023 atoms

NOTE: the mole is abbreviated mol (gee, that’s a lot quicker to write……)

Molar Mass• Mass of 1 ______ of a pure

substance• Numerically equal to the atomic

mass but expressed in _______• The atomic mass of carbon is

12.0____, so the molar mass of carbon is 12.0_____

•What is the molar mass of the following:

• Potassium ?

Nickel ?

•What is the atomic mass of the following:

• Potassium ?

Nickel ?

Practice • What is the molar mass of the

following:1. KCl2. C2H6

3. CaCO3

4. H2O

Homework/More Practice

• What is the molar mass of the following:

1. HCl2. NaCl3. CaO

Homework/More Practice

• Balance the following___Na + ____H2O ___H2 + ___NaOH

___C2H6 + ____O2 ___CO2 + ___H2O

Beaker Breaker• Calculate the molar mass of the

following:

• MgCl2

• CaBr2

Gram- Mole Conversions

How many grams are needed to have 0.852 moles gold?

• 0.852 mol Au g Au 1 mol Au

= ______g Au

Convert 2.50moles of KClO3 to grams

Calculate how many grams are in 0.700moles of H2O2?

How many moles are in 55 g of lead?

• g Pb mol Pb 1 g Pb

• = _______moles Pb

How many moles are in 86.1 g sodium?

• 86.1 g ? mole Na = 1 ? g

• 86.1 g mole Na = 1 g• _______moles Na

How many moles are in 22 grams of copper metal?

7-2 Types of Reactions• General types of chemical reactions1. ______________2. ______________3. ______________4. ______________5. ______________

Single Replacement• ________________ reaction is a

reaction in which one element takes place of another element in a compound.

• A + BC B + AC

Teacher Demonstration• See handout

• Cu + 2AgNO3 2Ag + Cu(NO3)2

• Copper replaces the silver nitrate to form copper(II) nitrate

• The products is_______, which you can see. The other product is_____________, gives the solution its blue color.

7-2 Continued Reactions as Electron Transfer

• The discovery of subatomic particles enabled scientists to classify certain chemical reactions as transfers of_______________ between atoms.

• A reaction in which electrons are transferred from one reactant to another is called an ____________________ reaction, _________ reaction

Oxidation• Synthesis reactions, in which

a____________combines with__________, traditionally have been classified as oxidations.

• 2Ca +O2 2_________• Ca Ca+2 + 2e-• Calcium ________ two electrons• A reactant is_________ if it loses

electrons

Reduction• As calcium atoms lose electrons during the

synthesis of calcium oxide, the oxygen________ electrons

• O + 2e- O2-

• The process in which an element gains electrons during a chemical reaction is called____________

• A reactant is said to be______________ if it gains electrons.

• Oxidation and reduction always occur________.

Beaker Breaker• Identify the following reactions as

either synthesis, decomposition, single replacement, double replacement, or combustion:

2C2H6 + 7O2 4CO2 + 6H2O

Ca + 2HCl CaCl2 + H2

Beaker Breaker Cont.• Write a paragraph explaining why

the formation of water can be classified as a synthesis or combustion.

7-3 Energy Changes in Reactions

Chemical Bonds and Energy• Heat produced by a_________(C3H8) grill

is a form of energy• Balance equation:• C3H8 + ____O2 ___CO2 +___H2O

• _________ will be added to the right side of the equation

Propane Combustionusing models

• C3H8 + 5O2 3CO2 + 4H2O

• Open to page 207 follow Figure 17

Chemical Energy• _____________ is the energy stored

in the chemical bonds of a substance.

• Using the models to make C3H8 (propane)• How many C-H bonds_________• How many C-C bonds_________

Chemical Bonds• Chemical _________ involve the________ of

chemical bonds in the __________ and the_______ of chemical bonds in the ________.

• Each propane molecule reacts with_______ oxygen molecules.

• In order for the reaction to occur, the ____ C-H single bonds, _____ C-C single bonds and____O=O double bonds must be broken.

• Breaking bonds require energy• Propane grills require a igniter to provide

enough energy to ________the bonds

Chemical Bonds• After the reaction of propane (it is burned)

occurs, ______molecules of carbon dioxide (CO2) and ______ molecules of water (H2O) are formed.

• There is _____ C=O double bonds and ____ O-H single bonds formed as the ________.

• Forming bonds__________ energy• ________and ________ given off by a propane

stove are the results from the formation of the new chemical bonds

Homework• Section 7-2 Review• #1 , 3, 4, 5

Beaker Breaker• Identify the following reactions as either single

displacement, double displacement, decomposition, synthesis, or combustion

1. NaCl + H2SO4 K2SO4 + H2O

2. CaO + CO2 CaCO3

3. MgCl2 Mg + Cl2

7-3 ContinuedExothermic and Endothermic

Reactions• During a chemical reaction, energy is

either ________ or ___________• A chemical reaction that_________

energy to its surroundings is called an_____________ reaction

• Ex: Freezing• A chemical reaction that__________

energy from its surroundings is called an____________

• Ex: Melting

Exothermic Reactions• In exothermic reactions, the energy

released as the products form is __________ than the energy required to break the bonds in the reactants

• Example – Combustion• C3H8 + 5O2 3CO2 + 4H2O +

2220kJ

Endothermic Reactions• In an endothermic reaction, more

energy is required to___________ the bonds in the reactants than is released by the formation of the products.

• Example: The decomposition of mercury (II) oxide

• 2HgO + 181.7kJ 2Hg + O2

Conservation of Energy• The law of____________________

states in exothermic and endothermic reactions the total amount of energy before and after the reaction is the same.

Homework • 7-3 Section Review page 209• Numbers 1,2,3

Ticket Out the Door• Please explain in a few sentences

how melting is an example of an endothermic reaction

7-4 Reaction Rates• A ________________ is the rate at

which reactants change into products over time.

• Reaction rates tell you how_______ a reaction is going

Factors Affecting Reaction Rates

• Factors that affect reaction rates include:1. ___________, 2. _____________, 3. _____________ 4. _____________5. ______________• Involve ___________ between particles• Reaction rate depends on how often these

particles _________

Temperature• An_________ in temperature will

_________the reaction rate• Ex. Frying an egg• ________ the temp will ________ the

reaction rate.• Ex: refrigerating milk to prevent spoiling• Increasing the ________, increases the

number of collisions between the particles, then _________ increases

Surface Area• The ________ the particle size of a given

mass, the _______ is its surface area.• An increase in _________ increases the

__________ of reactants to one another.• The __________this exposure, the more

collisions there are that involve reacting particles.

• ________ the surface area of a reactant tends to__________ the reaction rate.

Beaker Breaker• A__________rate is the rate at which

reactants change into products over time

• List two factors that affect reaction rates:

• An __________ in temperature will_________ the reaction rate

Stirring• You can ____________ the exposure of

reactants to each other by _________• Ex: washing machine• Stirring _____________ the reaction.• ____________ between the particles of

the reactants are more likely to happen

Concentration• _____________ refers to the number of

particles in a given volume• Ex: concentrated dyes• The reaction rate is ___________• For gases, concentration changes

with_______________ of a gaseous reactant, the __________ is its concentration, and the_________ the reaction rate.

Catalysts• A ___________ is a substance that affects

the reaction rate without being used up in the reaction.

• Chemists use catalysts to____________ a reaction or enable a reaction to occur at ___________ temperatures.

• Since the catalyst is neither a reactant nor a product, it is written ________ the arrow.

7-5 Equilibrium• _____________ is a state in which the

forward and reverse paths of change can take place at the ________ rate.

• Recall that changes to matter are either physical or chemical.

• When ___________ chemical changes take place at the same rate, a chemical equilibrium is reached

Physical Equilibrium• When a __________ change does

not go to completion, a physical equilibrium is established between the forward and reverse changes

• Ex: H2O (l) H2O(g)_________and___________are both

physical changes

Chemical Equilibrium• A ___________ reaction is a reaction in

which the conversion of reactants into products and the conversion of products into reactants can happen simultaneously

• When a chemical reaction does not go to completion, a ________________ is established between the forward and reverse reactions.

• Ex: 2SO2 (g) + O2 2SO3 (g) • Synthesis and decomposition

Factors Affecting Chemical Equilibrium

• When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that ________ the change.

• Principle was created by__________________

• Ex: N2 + 3H2 2NH3 + Heat

Temperature• N2 + 3H2 2NH3 + Heat• Synthesis of ammonia, heat is written

as a product• Forward reaction is ___________• Reverse is decomposition and is

____________•

Adding heat would then favor the______________reaction, which is endothermic

Pressure• __________ the pressure of the system,

equilibrium would shift in the direction that __________ the pressure of the system.

• Decreasing the pressure, the system would favor the reaction that produces__________gas molecules.

• Left Side has 4 gas molecules and right side has 2, so equilibrium would shift to the ________ when increasing the pressure

Concentration• Removing ammonia from the

system, Le Chatelier’s principle says that the equilibrium would shift in the direction that_________ ammonia

• In order to produce ammonia, the system would favor the __________reaction

Complete the following• Page 219 # 1,2,3,4, 5,