chemical reactions chp 21. chemical reactions section1 chemical reactions slides 3-20 section 2...

Chemical ReactionsChemical Reactions

Chp 21Chp 21

Chemical Reactions Chemical Reactions

Section1 Chemical Reactions slides 3-20Section1 Chemical Reactions slides 3-20 Section 2 Chemical Equations Section 2 Chemical Equations slides 21-34slides 21-34 Section 3 Classifying Chemical Reactions Section 3 Classifying Chemical Reactions

slides 35-46slides 35-46 Sections 4 Chemical Reactions & Energy Sections 4 Chemical Reactions & Energy

slides 47-61slides 47-61

Section 1 Chemical Section 1 Chemical ChangesChanges

What You’ll Learn:What You’ll Learn: How to identify the reactants & products How to identify the reactants & products

in a chemical reactionin a chemical reaction How a chemical reaction follows the law How a chemical reaction follows the law

of conservation of massof conservation of mass How chemists describe chemical How chemists describe chemical

changes with equationschanges with equations

Describing Chemical Describing Chemical RXNsRXNs

Chemical reactions happen all around Chemical reactions happen all around you & even inside your body!you & even inside your body!

A A chemical reaction chemical reaction is a change in is a change in which one or more substances are which one or more substances are converted into new substances.converted into new substances.


Chemical reactions happen all around Chemical reactions happen all around you & even inside your body!you & even inside your body!

A A chemical reaction chemical reaction is a change in is a change in which one or more substances are which one or more substances are converted into new substances.converted into new substances.

A A reactant reactant is one of the substances that is one of the substances that react. A react. A product product is one of the new is one of the new substances that are produced.substances that are produced.


Reactants Reactants products products produceproduce

A A reactant reactant is one of the substances that is one of the substances that react. A react. A product product is one of the new is one of the new substances that are produced.substances that are produced.

Conservation of MassConservation of Mass

Antoine Lavoisier Antoine Lavoisier discovered that discovered that the the total mass of the total mass of the products of a RXN products of a RXN always equals the always equals the mass of the mass of the reactants. reactants. He showed He showed the mass of a candle the mass of a candle and the air in a jar is the and the air in a jar is the same as the mass of the same as the mass of the products after burning.products after burning.

What were Lavoisier’s What were Lavoisier’s experiments?experiments?

He wanted to know exactly what He wanted to know exactly what happened when substances changed happened when substances changed form so he exform so he expperimented with mercury.erimented with mercury.


He wanted to know exactly what He wanted to know exactly what happened when substances changed happened when substances changed form so he exform so he expperimented with mercury.erimented with mercury.

He put solid mercury (II) oxide, a red He put solid mercury (II) oxide, a red powder, in a sealed containerpowder, in a sealed container,, found it found itss mass and then heated the container so mass and then heated the container so that the powder changed to a silvery that the powder changed to a silvery liquid, metal mercury, after giving off a liquid, metal mercury, after giving off a gas.gas.


Then he took the mass of the products in Then he took the mass of the products in the container which remained the same the container which remained the same as before.as before.

Mercury (II) oxide oxygen + mercuryMercury (II) oxide oxygen + mercury 10 g10 g = 0.3 g + 9.7 g = 0.3 g + 9.7 g


He also realized the gas produced, He also realized the gas produced, oxygen, was a part of air. oxygen, was a part of air.

Air combined with the mercury metal Air combined with the mercury metal when heated to make mercury (II) oxide. when heated to make mercury (II) oxide.

He studied the effect of oxygen on living He studied the effect of oxygen on living animals and humans.animals and humans.

In hundreds of experiments in his lab he In hundreds of experiments in his lab he confirmed the law of conservation of confirmed the law of conservation of mass.mass.

Why is Lavoisier called the Why is Lavoisier called the father of modern chemistry?father of modern chemistry?

His explanation of His explanation of the law of the law of conservation of mass conservation of mass started modern started modern science.science.

He was the first to He was the first to describe a chemical describe a chemical RXN called RXN called combustion.combustion.

Why are names Why are names important?important?

In 1787, Lavoisier & other scientists In 1787, Lavoisier & other scientists wrote the first instructions for naming wrote the first instructions for naming compounds because they needed a compounds because they needed a better way to describe their ideas so they better way to describe their ideas so they could clearly understand each other. could clearly understand each other.

Why are names Why are names important?important?

In 1787, Lavoisier & other scientists In 1787, Lavoisier & other scientists wrote the first instructions for naming wrote the first instructions for naming compounds because they needed a compounds because they needed a better way to describe their ideas so they better way to describe their ideas so they could clearly understand each other. could clearly understand each other.

The guidelines continue to evolve. In The guidelines continue to evolve. In 1919, the Intn’l Union of Pure & Applied 1919, the Intn’l Union of Pure & Applied Chemistry (IUPAC) was formed to Chemistry (IUPAC) was formed to coordinate guidelines. coordinate guidelines.

Writing EquationsWriting Equations

It’s important to include all the info when It’s important to include all the info when you describe a RXN. you describe a RXN.

The shortcut method to describe the RXN The shortcut method to describe the RXN is called a is called a chemical equation chemical equation & uses & uses chemical formulas & other symbols.chemical formulas & other symbols.

Symbols used in Symbols used in Chemical EquationsChemical Equations

SymbolSymbol MeaningMeaning SymbolSymbol MeaningMeaning

Produces or Produces or formsforms

(aq)(aq) Aqueous, Aqueous, dissolved in waterdissolved in water

++ plusplus HeatHeat

Reactants are Reactants are heatedheated

(s)(s) solidsolid LightLight

Reactants are Reactants are exposed to lightexposed to light

(l)(l) liquidliquid Elec.Elec.

Current applied Current applied to reactantsto reactants

(g)(g) gasgas

Writing EquationsWriting Equations

Nickel (II) chloride, dissolved in water, pus Nickel (II) chloride, dissolved in water, pus sodium hydroxide, dissolved in water, sodium hydroxide, dissolved in water, produces solid nickel (II) hydroxide plus produces solid nickel (II) hydroxide plus sodium chloride, dissolved in water.sodium chloride, dissolved in water.

OROR NiClNiCl2 2 ((aq) + 2aq) + 2NaOH (NaOH (aqaq) ) Ni(OH) Ni(OH)2 2 ((ss) + ) +

2NaCl (2NaCl (aq)aq) Both statements mean the same thing!Both statements mean the same thing!

Unit ManagersUnit Managers

NiClNiCl22((aq) + 2aq) + 2NaOH(NaOH(aqaq) ) Ni(OH) Ni(OH)22((ss))+2NaCl(+2NaCl(aq)aq)

A A coefficient coefficient shows the number of units of a shows the number of units of a substance taking part in a reaction.substance taking part in a reaction.

Atoms are rearranged but they are never Atoms are rearranged but they are never destroyed.destroyed.

Count the atoms on both sides of the Count the atoms on both sides of the equation above. Are they equal?equation above. Are they equal?

How do chemists use How do chemists use coefficients?coefficients?

When chemists know the number of units When chemists know the number of units of each reactant, they are able to add the of each reactant, they are able to add the correct amounts of reactants for a correct amounts of reactants for a reaction. The units or coefficients tell reaction. The units or coefficients tell how much product will form.how much product will form.

How do chemists use How do chemists use coefficients?coefficients?

NiClNiCl22((aq) + 2aq) + 2NaOH(NaOH(aqaq) ) Ni(OH) Ni(OH)22((ss))

+2NaCl(+2NaCl(aq)aq)

Ni+2

Cl

Cl

Ni+2

Cl

Cl

Na

Na

Na

Na

+

OH

OH

OH

OH +

Section 2 Chemical Section 2 Chemical EquationsEquations

What You’ll Learn:What You’ll Learn: What a balanced equation isWhat a balanced equation is How to write a balanced chemical How to write a balanced chemical

equationequation

2 Balanced Equations2 Balanced Equations

Lavoisier’s mercury (II) oxide RXN: Lavoisier’s mercury (II) oxide RXN: heatheat

HgOHgO(s)(s) Hg Hg(l)(l) + O + O22(g)(g)

Count the numbers of atoms on each Count the numbers of atoms on each side. What do you notice?side. What do you notice?

2 Balanced Equations2 Balanced Equations

Lavoisier’s mercury (II) oxide RXN: Lavoisier’s mercury (II) oxide RXN: heatheat

HgOHgO(s)(s) Hg Hg(l)(l) + O + O22(g)(g) Count the numbers of atoms on each Count the numbers of atoms on each

side. What do you notice?side. What do you notice? How can we make the oxygen balance How can we make the oxygen balance

without changing the compound without changing the compound produced?produced?

Balanced EquationsBalanced Equations

AtomsAtoms HgOHgO HgHg ++ OO22

HgHg 11 11

OO 11 22

What does a balanced What does a balanced equation show?equation show?

To balance a chemical equation, you To balance a chemical equation, you change the coefficients.change the coefficients.

A A balanced chemical equation balanced chemical equation has the has the same number of atoms of each element same number of atoms of each element on each side of the equation.on each side of the equation.

How do you choose How do you choose coefficients?coefficients?

Guess & checkGuess & check


AtomsAtoms 2HgO2HgO HgHg ++ OO22

HgHg 22 11

OO 22 22

This balances the oxygen but not the mercury. This balances the oxygen but not the mercury. Let’s try a 2 in front of the mercury on the right Let’s try a 2 in front of the mercury on the right side…side…


AtomsAtoms 2HgO2HgO 2Hg2Hg ++ OO22

HgHg 22 22

OO 22 22

Now the equation is balanced with equal Now the equation is balanced with equal numbers of each atom on reactant and product numbers of each atom on reactant and product sides.sides.

What are the steps for What are the steps for balancing an equation?balancing an equation?

Write a balanced chemical equation for Write a balanced chemical equation for the burning of magnesium:the burning of magnesium:

Step 1 Step 1 Write a chemical equation with Write a chemical equation with symbols and formulas.symbols and formulas.

Ex. MgEx. Mg(s) (s) + O+ O22(g)(g) MgO MgO(s)(s) Remember oxygen is a diatomic Remember oxygen is a diatomic

molecule with 2 oxygen atoms in a molecule with 2 oxygen atoms in a covalent bond.covalent bond.


Step 2 Step 2 Count the atoms in the reactants & Count the atoms in the reactants & products.products.

The magnesium atoms are balanced, but the The magnesium atoms are balanced, but the oxygen atoms are not.oxygen atoms are not.

AtomsAtoms MgMg ++ OO22 MgOMgO

MgMg 11 11

OO 22 11


Step 3 Step 3 Choose coefficients to balance the Choose coefficients to balance the equation.equation.

You cannot change subscripts of a formula to You cannot change subscripts of a formula to balance an equation.balance an equation.

AtomsAtoms MgMg ++ OO22 2MgO2MgO

MgMg 11 22

OO 22 22


Step 4 Step 4 Check the number of atoms on each Check the number of atoms on each side. side.

You need to add the coefficient 2 in front of the You need to add the coefficient 2 in front of the magnesium to balance the equation.magnesium to balance the equation.

AtomsAtoms 2Mg2Mg ++ OO22 2MgO2MgO

MgMg 22 22

OO 22 22

Now Try Balancing This:Now Try Balancing This:

______Fe + ___ClFe + ___Cl2 2 ___FeCl___FeCl33

a ba b c c

Now Try Balancing This:Now Try Balancing This:

______Fe + ___ClFe + ___Cl2 2 ___FeCl___FeCl33

a ba b c c

2Fe + 3 Cl2Fe + 3 Cl2 2 2Fe Cl2Fe Cl33

Section 3 Classifying Section 3 Classifying Chemical EquationsChemical Equations

What You’ll Learn:What You’ll Learn: What the five kinds of chemical reactions What the five kinds of chemical reactions

areare What oxidation & reduction areWhat oxidation & reduction are What a redox reaction isWhat a redox reaction is Which metals replace others in Which metals replace others in

compoundscompounds

3 Types of Reactions3 Types of Reactions

Scientists organize or classify reactions Scientists organize or classify reactions into five types:into five types: CombustionCombustion SynthesisSynthesis DecompositionDecomposition Single displacementSingle displacement Double displacementDouble displacement

What are combustion What are combustion reactions?reactions?

A A combustion reaction combustion reaction occurs when a occurs when a substance reacts with oxygen to produce substance reacts with oxygen to produce heat and light. Ex. Burning something.heat and light. Ex. Burning something.

Combustion produces one or more Combustion produces one or more products that contain elements of the products that contain elements of the reactants. Sometimes combustion RXNs reactants. Sometimes combustion RXNs are also other types of reactions at the are also other types of reactions at the same time.same time.

What are synthesis What are synthesis RXNs?RXNs?

In a In a synthesis reaction,synthesis reaction, 2 or more 2 or more substances combine to form another substances combine to form another substance. The general formula is substance. The general formula is A +B A +B AB or A reacts with B to form AB or A reacts with B to form AB.AB.

An example is hydrogen burning in An example is hydrogen burning in oxygen to form water:oxygen to form water:

2H2H22(g) + (g) + OO22(g)(g) 2H 2H22OO(g)(g)

What are synthesis What are synthesis RXNs?RXNs?

An example is hydrogen burning in An example is hydrogen burning in oxygen to form water:oxygen to form water:

2H2H22(g) + (g) + OO22(g)(g) 2H 2H22OO(g)(g) This RXN is used to power some rockets, This RXN is used to power some rockets,

including the main engines of a space including the main engines of a space shuttle.shuttle.

Rust is another product of a synthesis Rust is another product of a synthesis RXN between iron and oxygen.RXN between iron and oxygen.

What are decomposition What are decomposition RXNs?RXNs?

The reverse of a synthesis RXN, The reverse of a synthesis RXN, decomposition reaction decomposition reaction occurs when occurs when one substance breaks down into 2 or one substance breaks down into 2 or more substances with the general more substances with the general formula of AB formula of AB A + B. A + B.

Most decomposition RXNs use heat, light Most decomposition RXNs use heat, light or electricity.or electricity.

What are decomposition What are decomposition RXNs?RXNs?

An electric current An electric current passed through passed through water produces water produces hydrogen and hydrogen and oxygen. This oxygen. This reaction is also reaction is also referred to as referred to as electrolysis.electrolysis.

What are single- What are single- displacement RXNs?displacement RXNs? A A single-displacement reaction single-displacement reaction happens happens

when one element replaces another element when one element replaces another element in a compound. The general formula for it is in a compound. The general formula for it is A+BC A+BC AC+B.AC+B.

Atom A displaces atom B forming a new Atom A displaces atom B forming a new molecule AC. Ex. When copper wire is put in molecule AC. Ex. When copper wire is put in a solution of silver nitrate: Cua solution of silver nitrate: Cu(s)(s)+2AgNO+2AgNO33(aq) (aq) Cu(NOCu(NO33))22(aq)(aq)+ 2Ag+ 2Ag(s)(s)

What is the activity What is the activity series?series? You can predict which You can predict which

metal will replace metal will replace another metal in another metal in displacement RXNs.displacement RXNs.

The diagram lists metals The diagram lists metals by how reactive they are by how reactive they are with the most active at with the most active at the top & least active at the top & least active at the bottom. the bottom.

Note: Cu, Ag & Au Note: Cu, Ag & Au found in relatively pure found in relatively pure deposits.deposits.

What are double-What are double-displacement RXNs?displacement RXNs?

The positive ion of one compound The positive ion of one compound replaces the positive ion of the other replaces the positive ion of the other compound to form two new compounds. compound to form two new compounds. The general formula is: The general formula is: AB +CD AB +CD AD +CB. AD +CB.

An example…. Ba(NOAn example…. Ba(NO33))22((aq)aq) + K + K22SOSO44(aq) (aq)

BaSO BaSO44(s) + (s) + 2KNO3(aq)

What are oxidation-What are oxidation-reduction reactions?reduction reactions?

In many RXNs, substances gain or lose In many RXNs, substances gain or lose electrons. electrons. Oxidation Oxidation is a loss of is a loss of electrons during a chemical reaction. electrons during a chemical reaction. ReductionReduction is a gain of electrons during a is a gain of electrons during a chemical RXN. Electron transfer often chemical RXN. Electron transfer often involves oxygen; because it’s very involves oxygen; because it’s very reactive, it often pulls electrons from reactive, it often pulls electrons from metals causing them to corrode or rust.metals causing them to corrode or rust.

What are oxidation-What are oxidation-reduction reactions?reduction reactions?

The substance that The substance that gains electrons gains electrons becomes negative so becomes negative so it is it is reduced.reduced.

The substance that The substance that loses electrons loses electrons becomes more becomes more positive or oxidized.positive or oxidized.

Redox- redRedox- reduction-uction-oxoxidationidation

Section 4 Chemical Section 4 Chemical Reactions & EnergyReactions & Energy

What You’ll Learn:What You’ll Learn: Energy changes sources in chemical Energy changes sources in chemical

reactionsreactions The difference between exergonic & The difference between exergonic &

endergonic reactionsendergonic reactions How catalysts & inhibitors are usedHow catalysts & inhibitors are used

4 Chemical RXNs & 4 Chemical RXNs & EnergyEnergy

Dynamite can be used to demolish old Dynamite can be used to demolish old buildings. A dynamite explosion is an buildings. A dynamite explosion is an example of a rapid chemical RXN.example of a rapid chemical RXN.



All chemical RXNs either release or All chemical RXNs either release or absorb energy in the form of heat, light, absorb energy in the form of heat, light, sound or electricity.sound or electricity.



All chemical RXNs either release or All chemical RXNs either release or absorb energy in the form of heat, light, absorb energy in the form of heat, light, sound or electricity.sound or electricity.

Chemical bonds are the source of this Chemical bonds are the source of this energy.energy.

More Energy OutMore Energy Out

AnAn exergonic reaction exergonic reaction releases energy. releases energy. Less energy is needed to break the Less energy is needed to break the bonds in the reactants than is released bonds in the reactants than is released when the new bonds in the products when the new bonds in the products form. Exergonic reactions give off form. Exergonic reactions give off energy such as heat or light like that from energy such as heat or light like that from a glow stick.a glow stick.

What are exothermic What are exothermic reactions?reactions?

A reaction with energy given off as heat is an A reaction with energy given off as heat is an exothermic RXN. exothermic RXN.

Heat packs, burning wood, rusting iron and Heat packs, burning wood, rusting iron and exploding dynamite are examples.exploding dynamite are examples.

What are exothermic What are exothermic reactions?reactions?

The energy you are using today probably came The energy you are using today probably came from exothermic RXNs at a power plant that from exothermic RXNs at a power plant that burns fossil fuels. Other products of that RXN burns fossil fuels. Other products of that RXN include pollutants such as sulfur dioxide.include pollutants such as sulfur dioxide.

More Energy InMore Energy In

An An endergonic reaction endergonic reaction absorbs energy absorbs energy since it takes more energy to break the since it takes more energy to break the bonds in the reactants than is released bonds in the reactants than is released when new bonds in the products form.when new bonds in the products form.



Endergonic RXNs absorb energy such as Endergonic RXNs absorb energy such as heat, light or electricity.heat, light or electricity.



Endergonic RXNs absorb energy such as Endergonic RXNs absorb energy such as heat, light or electricity.heat, light or electricity.

ElectroplatingElectroplating puts a coat of metal onto puts a coat of metal onto a surface. Electricity is also used to a surface. Electricity is also used to separate aluminum metal from ore.separate aluminum metal from ore.


In the following endergonic reaction, In the following endergonic reaction, energy from electricity keeps the reaction energy from electricity keeps the reaction going.going.

electricityelectricity

2 Al2 Al22OO33(l) (l) 4Al 4Al(l) (l) + 3O+ 3O22(g)(g)

What is an endothermic What is an endothermic RXN?RXN?

An An endothermic reactionendothermic reaction absorbs absorbs energy, usually as heat. When an energy, usually as heat. When an endothermic RXN takes place in a endothermic RXN takes place in a beaker, it can make the beaker feel cold. beaker, it can make the beaker feel cold. Physical changes also can be described Physical changes also can be described as endothermic such as salt dissolving in as endothermic such as salt dissolving in water or ice like that in an ice cream water or ice like that in an ice cream freezer.freezer.

What is an endothermic What is an endothermic RXN?RXN?

When barium hydroxide reacts with When barium hydroxide reacts with ammonium chloride in a beaker of water, ammonium chloride in a beaker of water, it is so endothermic that it causes a drop it is so endothermic that it causes a drop of water on the outside of the beaker to of water on the outside of the beaker to freeze. freeze.

Cold packs contain ammonium nitrate Cold packs contain ammonium nitrate crystals and water.crystals and water.

What are catalysts?What are catalysts?

A A catalyst catalyst is a substance that speeds up is a substance that speeds up a chemical RXN without being a chemical RXN without being permanently changed itself. permanently changed itself.

The catalyst can be recovered and The catalyst can be recovered and reused.reused.

What are inhibitors?What are inhibitors?

Sometimes, it is helpful to prevent or to Sometimes, it is helpful to prevent or to slow down chemical reactions with an slow down chemical reactions with an inhibitor. inhibitor.

Like catalysts, inhibitors do not change Like catalysts, inhibitors do not change the amount of product produced in a the amount of product produced in a RXN.RXN.

Food preservatives called BHT & BHA Food preservatives called BHT & BHA are inhibitors that prevent food spoilage.are inhibitors that prevent food spoilage.

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