Chapter 7 Chemical Reactions 7 1 Describing Reactions

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Chapter 7 Chemical Reactions

Chapter 7 Chemical Reactions

7 -1 Describing Reactions • In a chemical reaction, the substances that undergo change

7 -1 Describing Reactions • In a chemical reaction, the substances that undergo change are called reactants • The new substances formed as a result of that change are called products • Reactants Products • Ex. Carbon + oxygen carbon dioxide • Word equation

Chemical equations • Ex. C + O 2 CO 2 • Chemical formula •

Chemical equations • Ex. C + O 2 CO 2 • Chemical formula • A chemical equation is a representation of a chemical reaction in which the reactants and products are expressed as formulas

Conservation of Mass • During chemical reactions, the mass of the products is always

Conservation of Mass • During chemical reactions, the mass of the products is always equal to the mass of the reactants. • Established by Antoine Lavoisier and is known as the law of conservation of mass • The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction

How is mass conserved in chemical change? Activity • Follow the directions on page

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 10 cm_________ • 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 questions 1. How do you know whether a chemical change took place?

Activity questions 1. How do you know whether a chemical change took place?

Activity Question • What happened to the mass of the plastic bag and its

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?

Beaker Breaker 1. A chemical_____ is a representation of a chemical reaction in which

Beaker Breaker 1. A chemical_____ is a representation of a chemical reaction in which the reactants and products are expressed as formulas 2. True or False mass can be destroyed during a chemical reaction. 3. In the equation H 2 + O H 2 O write the symbols that represent the reactants.

Balancing Equations 7 -1 Continued • In order to show that mass is conserved

Balancing Equations 7 -1 Continued • In order to show that mass is conserved during a reaction, a chemical equation must be balanced • You can balance a chemical equation by changing the coefficients, the numbers that appear before the formulas • As you balance equations, you should never change the subscripts in a formula

Steps to balancing equations 1. Count the number of atoms of each element on

Steps to balancing equations 1. Count the number of atoms of each element on each side of the equation 2. Ex: N 2 H 4 + O 2 N 2 + H 2 O 3. Left side has 2 nitrogen, four hydrogen, and 2 oxygen atoms 4. The right side has 2 nitrogen, 2 hydrogen, and 1 oxygen atom 5. The hydrogen and oxygen atoms need to be balanced.

Steps to balancing equations 6. Change one or more coefficients until the equation is

Steps to balancing equations 6. Change one or more coefficients until the equation is balanced _1_N 2 H 4 + _1_O 2 _1_N 2 + _2_H 2 O • • The equation is now balanced Each side has two nitrogen, 2 oxygen, and 4 hydrogen atoms

Practice Balancing equations problems 1. ___Na + ___H 2 O ____Na. OH + ___H

Practice Balancing equations problems 1. ___Na + ___H 2 O ____Na. OH + ___H 2 2. ___HCl + ___Ca. CO 3 ____Ca. Cl 2 +___CO 2 + ____H 2 O 3. ____Al + ____Cl 2 _____Al. Cl 3 4. ___Cu + _____O 2 _____Cu. O 5. ____H 2 O 2 ____H 2 O + ____O 2

Beaker Breaker • • • Balance the following equation _____Fe + _______Cl 2 ______Fe.

Beaker Breaker • • • Balance the following equation _____Fe + _______Cl 2 ______Fe. Cl 3 _______K + _______Br 2 ______KBr

Beaker Breaker • Balance the following equations • _______K + _______Br 2 ______KBr •

Beaker Breaker • Balance the following equations • _______K + _______Br 2 ______KBr • ______Mg + ____O 2 _______Mg. O

Scientists work with samples large enough for us to SEE and WEIGH on a

Scientists work with samples large enough for us to SEE and WEIGH on a balance using units of ……. GRAMS.

This Creates a Problem…… A pile of atoms big enough for us to see

This Creates a Problem…… A pile of atoms big enough for us to see contains billions of atoms. How do we keep track of that many atoms? ? ?

Development of the Term Mole The word “mole” was introduced about 1896 by Wilhelm

Development of the Term Mole The word “mole” was introduced about 1896 by Wilhelm Oswald, who derived the term from the Latin word moles meaning a “heap” or “pile”.

Avogadro’s Number Named in honor of Amadeo Avogadro (1776 – 1856) He studied gases

Avogadro’s Number Named in honor of Amadeo Avogadro (1776 – 1856) He studied gases and discovered that no matter what the gas, there were the same number of molecules present.

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

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

Just How Big is a Mole? 6. 02 X 1023 Pennies: Would make at

Just How Big is a Mole? 6. 02 X 1023 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

How Big is a mole? Cover the earth to a depth of 200 miles with soft drink cans. of 9 Cover the USA to a depth miles of unpopped popcorn kernels.

The mole is many things…. 1 dozen cookies = 12 cookies 1 mole of

The mole is many things…. 1 dozen cookies = 12 cookies 1 mole of cookies = 6. 02 x 1023 cookies cars 1 dozen cars = 12 cars 1 mole of cars = 6. 02 x 10 23 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6. 02 x 1023 atoms NOTE: the mole is abbreviated mol (gee, that’s a lot quicker to write……)

Everybody Dance Now!!!!!!! Moleshake My moleshake brings all the moles to the yard, And

Everybody Dance Now!!!!!!! Moleshake My moleshake brings all the moles to the yard, And they’re like, “Man, Chemistry’s hard” Yeah right, yeah Chemistry’s hard, I can teach you, and I won’t even charge.

Molar Mass • Mass of 1 mole of a pure substance • Numerically equal

Molar Mass • Mass of 1 mole of a pure substance • Numerically equal to the atomic mass but expressed in GRAMS • The atomic mass of carbon is 12. 0 amu, so the molar mass of carbon is 12. 0 grams

 • What is the molar mass of the following: • Potassium ? •

• What is the molar mass of the following: • Potassium ? • 39. 098 g (or 39. 098 g/mol) Nickel ? • 58. 693 g (or 58. 693 g/mol)

 • What is the atomic mass of the following: • Potassium ? •

• What is the atomic mass of the following: • Potassium ? • 39. 098 amu Nickel ? • 58. 693 amu

Practice • 1. 2. 3. 4. What is the molar mass of the following:

Practice • 1. 2. 3. 4. What is the molar mass of the following: KCl C 2 H 6 Ca. CO 3 H 2 O

Homework/More Practice • What is the molar mass of the following: 1. HCl 2.

Homework/More Practice • What is the molar mass of the following: 1. HCl 2. Na. Cl 3. Ca. O

Homework/More Practice • Balance the following ___Na + ____H 2 O ___H 2 +

Homework/More Practice • Balance the following ___Na + ____H 2 O ___H 2 + ___Na. OH ___C 2 H 6 + ____O 2 ___CO 2 + ___H 2 O

Beaker Breaker • Calculate the molar mass of the following: • Mg. Cl 2

Beaker Breaker • Calculate the molar mass of the following: • Mg. Cl 2 • Ca. Br 2

Dude!!! Atoms are REALLY small!!! We can’t work with individual atoms or mass individual

Dude!!! Atoms are REALLY small!!! We can’t work with individual atoms or mass individual atoms. BECAUSE……. . We can’t see things that small!

Gram- Mole Conversions

Gram- Mole Conversions

How many grams are needed to have 0. 852 moles gold? • 0. 852

How many grams are needed to have 0. 852 moles gold? • 0. 852 mol Au 1 = 168 g Au 196. 97 g Au 1 mol Au

Convert 2. 50 moles of KCl. O 3 to grams

Convert 2. 50 moles of KCl. O 3 to grams

Calculate how many grams are in 0. 700 moles of H 2 O 2?

Calculate how many grams are in 0. 700 moles of H 2 O 2?

How many moles are in 55 g of lead? • 55 g Pb 1

How many moles are in 55 g of lead? • 55 g Pb 1 1 mol Pb 207. 2 g Pb • = 0. 26 moles Pb

How many moles are in 86. 1 g sodium? • 86. 1 g ?

How many moles are in 86. 1 g sodium? • 86. 1 g ? mole Na = 1 ? g • • 86. 1 g 1 mole Na = 1 22. 99 g 3. 74 moles Na

How many moles are in 22 grams of copper metal?

How many moles are in 22 grams of copper metal?

7 -2 Types of Reactions • 1. 2. 3. 4. 5. General types of

7 -2 Types of Reactions • 1. 2. 3. 4. 5. General types of chemical reactions Synthesis Decomposition Single-replacement Double-replacement Combustion

Single Replacement • Single-replacement reaction is a reaction in which one element takes place

Single Replacement • 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 + 2 Ag. NO 3 2 Ag

Teacher Demonstration • See handout • Cu + 2 Ag. NO 3 2 Ag + Cu(NO 3)2 Copper replaces the silver nitrate to form copper(II) nitrate • The products is silver, which you can see. The other product is copper(II) nitrate, gives the solution its blue color. •

7 -2 Continued Reactions as Electron Transfer • The discovery of subatomic particles enabled

7 -2 Continued Reactions as Electron Transfer • The discovery of subatomic particles enabled scientists to classify certain chemical reactions as transfers of electrons between atoms. • A reaction in which electrons are transferred from one reactant to another is called an oxidation-reduction reaction, redox reaction

Oxidation • Synthesis reactions, in which a metal combines with oxygen, traditionally have been

Oxidation • Synthesis reactions, in which a metal combines with oxygen, traditionally have been classified as oxidations. • 2 Ca +O 2 2 Ca. O • Ca Ca+2 + 2 e • Calcium loses two electrons • A reactant is oxidized if it loses electrons

Reduction • As calcium atoms lose electrons during the synthesis of calcium oxide, the

Reduction • As calcium atoms lose electrons during the synthesis of calcium oxide, the oxygen gains electrons • O + 2 e- O 2 • The process in which an element gains electrons during a chemical reaction is called reduction • A reactant is said to be reduced if it gains electrons. • Oxidation and reduction always occur together.

Beaker Breaker • Identify the following reactions as either synthesis, decomposition, single replacement, double

Beaker Breaker • Identify the following reactions as either synthesis, decomposition, single replacement, double replacement, or combustion: 2 C 2 H 6 + 7 O 2 4 CO 2 + 6 H 2 O Ca + 2 HCl Ca. Cl 2 + H 2

Beaker Breaker Cont. • Write a paragraph explaining why the formation of water can

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

7 -3 Energy Changes in Reactions Chemical Bonds and Energy • Heat produced by a propane(C 3 H 8) grill is a form of energy • Balance equation: • C 3 H 8 + ____O 2 ___CO 2 +___H 2 O • Heat will be added to the right side of the equation

Propane Combustion using models • C 3 H 8 + 5 O 2 3

Propane Combustion using models • C 3 H 8 + 5 O 2 3 CO 2 + 4 H 2 O • Open to page 207 follow Figure 17

Chemical Energy • Chemical energy is the energy stored in the chemical bonds of

Chemical Energy • Chemical energy is the energy stored in the chemical bonds of a substance. • Using the models to make C 3 H 8 (propane) • How many C-H bonds_____ • How many C-C bonds_____

Chemical Bonds • Chemical reactions involve the breaking of chemical bonds in the reactants

Chemical Bonds • Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products. • Each propane molecule reacts with 5 oxygen molecules. • In order for the reaction to occur, the 8 C-H single bonds, 2 C-C single bonds and 5 O=O double bonds must be broken. • Breaking bonds require energy • Propane grills require a igniter to provide enough energy to break the bonds

Chemical Bonds • After the reaction of propane (it is burned) occurs, 3 molecules

Chemical Bonds • After the reaction of propane (it is burned) occurs, 3 molecules of carbon dioxide (CO 2) and 4 molecules of water (H 2 O) are formed. • There is 6 C=O double bonds and 8 O-H single bonds formed as the products. • Forming bonds releases energy • Heat and light 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

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

Beaker Breaker • Identify the following reactions as either single displacement, double displacement, decomposition,

Beaker Breaker • Identify the following reactions as either single displacement, double displacement, decomposition, synthesis, or combustion 1. Na. Cl + H 2 SO 4 K 2 SO 4 + H 2 O 2. Ca. O + CO 2 Ca. CO 3 3. Mg. Cl 2 Mg + Cl 2

7 -3 Continued Exothermic and Endothermic Reactions • During a chemical reaction, energy is

7 -3 Continued Exothermic and Endothermic Reactions • During a chemical reaction, energy is either released or absorbed • A chemical reaction that releases energy to its surroundings is called an exothermic reaction • Ex: Freezing • A chemical reaction that absorbs energy from its surroundings is called an endothermic • Ex: Melting

Exothermic Reactions • In exothermic reactions, the energy released as the products form is

Exothermic Reactions • In exothermic reactions, the energy released as the products form is greater than the energy required to break the bonds in the reactants • Example – Combustion • C 3 H 8 + 5 O 2 3 CO 2 + 4 H 2 O + 2220 k. J

Endothermic Reactions • In an endothermic reaction, more energy is required to break the

Endothermic Reactions • In an endothermic reaction, more energy is required to break the bonds in the reactants than is released by the formation of the products. • Example: The decomposition of mercury (II) oxide • 2 Hg. O + 181. 7 k. J 2 Hg + O 2

Conservation of Energy • The law of conservation of energy states in exothermic and

Conservation of Energy • The law of conservation of energy 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

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

Ticket Out the Door • Please explain in a few sentences how melting is

Ticket Out the Door • Please explain in a few sentences how melting is an example of an endothermic reaction

7 -4 Reaction Rates • A reaction rate is the rate at which reactants

7 -4 Reaction Rates • A reaction rate is the rate at which reactants change into products over time. • Reaction rates tell you how fast a reaction is going

Factors Affecting Reaction Rates • 1. 2. 3. 4. 5. • • Factors that

Factors Affecting Reaction Rates • 1. 2. 3. 4. 5. • • Factors that affect reaction rates include: temperature, surface area, concentration, stirring, catalysts. Involve collisions between particles Reaction rate depends on how often these particles collide

Temperature • An increase in temperature will increase the reaction rate • Ex. Frying

Temperature • An increase in temperature will increase the reaction rate • Ex. Frying an egg • decrease the temp will decrease the reaction rate. • Ex: refrigerating milk to prevent spoiling • Increasing the temp, increases the number of collisions between the particles, then reaction rate increases

Surface Area • The smaller the particle size of a given mass, the larger

Surface Area • The smaller the particle size of a given mass, the larger is its surface area. • An increase in surface area increases the exposure of reactants to one another. • The greater this exposure, the more collisions there are that involve reacting particles. • Increasing the surface area of a reactant tends to increase the reaction rate.

Beaker Breaker • • • A_____rate is the rate at which reactants change into

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 increase the exposure of reactants to each other by stirring

Stirring • You can increase the exposure of reactants to each other by stirring • Ex: washing machine • Stirring speeds up the reaction. • Collisions between the particles of the reactants are more likely to happen

Concentration • Concentration refers to the number of particles in a given volume •

Concentration • Concentration refers to the number of particles in a given volume • Ex: concentrated dyes • The reaction rate is faster • For gases, concentration changes with pressure of a gaseous reactant, the greater is its concentration, and the faster the reaction rate.

Catalysts • A catalyst is a substance that affects the reaction rate without being

Catalysts • A catalyst is a substance that affects the reaction rate without being used up in the reaction. • Chemists use catalysts to speed up a reaction or enable a reaction to occur at lower temperatures. • Since the catalyst is neither a reactant nor a product, it is written over the arrow.

7 -5 Equilibrium • Equilibrium is a state in which the forward and reverse

7 -5 Equilibrium • Equilibrium is a state in which the forward and reverse paths of change can take place at the same rate. • Recall that changes to matter are either physical or chemical. • When opposing chemical changes take place at the same rate, a chemical equilibrium is reached

Physical Equilibrium • When a physical change does not go to completion, a physical

Physical Equilibrium • When a physical change does not go to completion, a physical equilibrium is established between the forward and reverse changes • Ex: H 2 O (l) H 2 O(g) Evaporation and Condensation are both physical changes

Chemical Equilibrium • A reversible reaction is a reaction in which the conversion of

Chemical Equilibrium • A reversible 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 chemical equilibrium is established between the forward and reverse reactions. • Ex: 2 SO 2 (g) + O 2 2 SO 3 (g) • Synthesis and decomposition

Factors Affecting Chemical Equilibrium • When a change is introduced to a system in

Factors Affecting Chemical Equilibrium • When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change. • Principal was created by Henri Le’Chatelier • Ex: N 2 + 3 H 2 2 NH 3 + Heat

Temperature • N 2 + 3 H 2 2 NH 3 + Heat •

Temperature • N 2 + 3 H 2 2 NH 3 + Heat • Synthesis of ammonia, heat is written as a product • Forward reaction is exothermic • Reverse is decomposition and is endothermic • Adding heat would then favor the reverse reaction, which is endothermic

Pressure • Increase the pressure of the system, equilibrium would shift in the direction

Pressure • Increase the pressure of the system, equilibrium would shift in the direction that decreases the pressure of the system. • Decreasing the pressure, the system would favor the reaction that produces fewer gas molecules. • Left Side has 4 gas molecules and right side has 2, so equilibrium would shift to the right in order to increase the pressure

Concentration • Removing ammonia from the system, Le Chatelier’s principle says that the equilibrium

Concentration • Removing ammonia from the system, Le Chatelier’s principle says that the equilibrium would shift in the direction that produces ammonia • In order to produce ammonia, the system would favor the forward reaction