Intro to Reactions (p. 241 – 250)

I II III IV VC. Johannesson

I. Intro to Reactions

(p. 241 – 250)

Ch. 8 – Chemical Reactions

C. Johannesson

A.Signs of a Chemical Reaction

Evolution of ________ and ________

Formation of a _______

Formation of a ___________

_________ change

C. Johannesson

B.Law of Conservation of Mass mass is neither created nor destroyed

in a chemical reaction

4 H

2 O

4 H

2 O4 g 32 g

36 g

total mass stays the same atoms can only rearrange

C. Johannesson

C. Chemical Equations

A+B C+DREACTANTS PRODUCTS

C. Johannesson

p. 246

C. Chemical Equations

C. Johannesson

D. Writing Equations

Identify the substances involved. Use symbols to show:

2H2(g) + O2(g) 2H2O(g)

How many? - coefficient

Of what? - chemical formula

In what state? - physical state Remember the diatomic elements.

D. Writing Equations

Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride.

• How many?• Of what?• In what state?

C. Johannesson

E. Describing Equations

Describing Coefficients:

individual atom = “atom”

covalent substance = “molecule”

ionic substance = “unit”

3 molecules of carbon dioxide

2 atoms of magnesium

4 units of magnesium oxide

3CO2

2Mg

4MgO

E. Describing Equations

• How many?• Of what?• In what state?

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)


II. Balancing Equations

(p. 250-254)


C. Johannesson

A. Balancing Steps

1. _________ the unbalanced equation.

2. _________ atoms on each side.

3. _____ coefficients to make #s equal.

Coefficient subscript = # of atoms

4. _________ coefficients to lowest possible ratio, if necessary.

5. Double check atom __________!!!

C. Johannesson

B. Helpful Tips

Balance one element at a time. Update ALL atom counts after adding

a coefficient. If an element appears more than

once per side, balance it last. Balance polyatomic ions as single

units. “1 SO4” instead of “1 S” and “4 O”

Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

C. Balancing Example

Aluminum and copper(II) chloride react to form copper and aluminum chloride.



III. Types of Chemical Reactions

(p. 256 - 267)

C. Johannesson

A. Combustion

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

the burning of any substance in O2 to produce heat

A + O2 BCH4(g) + 2O2(g) CO2(g) + 2H2O(g)

C. Johannesson

Na(s)+ O2(g)

C3H8(g)+ O2(g)

A. Combustion

Products: contain oxygen hydrocarbons form CO2 + H2O

CO2(g) + H2O(g)

Na2O(s) 4 2

C. Johannesson

B. _____________

the combination of 2 or more substances to form a compound

only one product

A + B AB

C. Johannesson

B. _____________

H2(g) + Cl2(g) 2 HCl(g)

C. Johannesson

Al(s)+ Cl2(g) AlCl3(s)

B. _____________

Products: ionic - cancel charges covalent - hard to tell

C. Johannesson

C. _______________

a compound breaks down into 2 or more simpler substances

only one reactant

AB A + B

C. Johannesson

C. ________________

2 H2O(l) 2 H2(g) + O2(g)

C. Johannesson

KBr(l) K(s) + Br2(l)

C. ________________

Products: binary - break into elements others - hard to tell

23

The “Activity Series” of Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead HydrogenHydrogen Bismuth Copper Mercury Silver Platinum Gold

1) Metals can replace other metals, provided they are above the metal they are trying to replace (for example, zinc will replace lead)

2) Metals above hydrogen can replace hydrogen in acids.

3) Metals from sodium upward can replace hydrogen in water.

Higher activity

Lower activity

24

The “Activity Series” of Halogens

Fluorine Chlorine Bromine Iodine

Halogens can replace other halogens in compounds, provided they are above the halogen they are trying to replace.

2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)

MgCl2(s) + Br2(g) ???No Reaction!

???

Higher Activity

Lower Activity

C. Johannesson

D. __________ ________________ one element replaces another in a

compound metal replaces metal (+) nonmetal replaces nonmetal (-)

A + BC B + AC

C. Johannesson

D. __________ ________________

Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

C. Johannesson

Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)

D. __________ ________________

Products: metal metal (+) nonmetal nonmetal (-) free element must be more active (check activity series)

Br2(l)+ NaCl(aq) N.R.

C. Johannesson

AB + CD AD + CB

E. __________ ________________ ions in two compounds “change partners” cation of one compound combines with

anion of the other

C. Johannesson

E. __________ ________________

Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)

C. Johannesson

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

E. __________ ________________ Products:

switch negative ions one product must be insoluble (check

solubility table)

NaNO3(aq)+ KI(aq) N.R.

2 2


IV. Reaction Energy

(p. 514 - 517)


C. Johannesson

A. Reaction Pathway

Shows the change in energy during a chemical reaction

C. Johannesson

B. _____________ Reaction

reaction thatreleases energy

products have lower PE than reactants

2H2(l) + O2(l) 2H2O(g) + energy

energyreleased

C. Johannesson

C. _____________ Reaction

reaction that absorbs energy

reactants have lower PE than products

2Al2O3 + energy 4Al + 3O2

energyabsorbed


V. Reaction Rate

(p. 532 - 541)


C. Johannesson

A. Collision Theory

Reaction rate depends on the collisions between reacting particles.

Successful collisions occur if the particles...

collide with each other

have the correct orientation

have enough kinetic energy to break bonds

C. Johannesson

A. Collision Theory

Particle Orientation

Required Orientation

Successful CollisionUnsuccessful

Collisions

C. Johannesson

A. Collision Theory

_____________ Energy (Ea)

minimum energy required for a reaction to occur

ActivationEnergy

C. Johannesson

A. Collision Theory

Activation Energy depends on reactants low Ea = fast rxn rate

Ea

C. Johannesson

B. Factors Affecting Rxn Rate

______________ __________ high SA = fast rxn rate more opportunities for collisions Increase surface area by…

-1.

-2.

C. Johannesson


_______________ high conc = fast rxn rate more opportunities for collisions

C. Johannesson

B. Factors Affecting Rxn Rate _______________

high temp = fast rxn rate

high KE

- fast-moving particles

-more likely to reach activation energy

C. Johannesson


Temperature

Analogy: 2-car collision

5 mph “fender bender”

50 mph “high-speed crash”

C. Johannesson


_______________ substance that increases rxn rate

without being consumed in the rxn lowers the activation energy

C. Johannesson


Enzyme Catalysis

Intro to Reactions (p. 241 – 250)

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