IIIIIIIVV S.Panzarella Chemical Reactions & Equations

I II III IV VS.Panzarella

Chemical Reactions & Equations

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Chemical Equations

A + B C + D

REACTANTS PRODUCTS

• Shows what takes place during a chemical reaction

•Reactant : (substances reacting) on left•Arrow - (→) at center ; yields or produces•Products: (new substances formed) on right

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Coefficients: how many? ; # appears in FRONT of the formula “molecules” for covalent substances

“moles“ of atoms “units” for ionic substances

3CO2

2Mg

4MgO

3 molecules of carbon dioxide

2 moles of magnesium

4 units of magnesium oxide

Phases: • solid (s), liquid (l), gas (g), aqueous (aq)

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Example:

Names of reactants: methane & oxygen Names of products: carbon dioxide & water

CH4 + 2O2 CO2 + 2H2O

How many of each (coefficient):

__CH4 ____O2 ____CO2 ___H2O

Ratio of coefficients: ___: ____: ___: ___

reactants products

1 2 1 2

11 2 2

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Expressing Chemical Equations

Word: carbon + oxygen yields carbon dioxide

Remember your diatomic gases: (BrINClHOF)

C + O2 → CO2

Formula

→+Diagram:

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Exothermic & Endothermic Processes – see RB pg 34 table 2.5

Exothermic: release energy; surrounding temp increases; NRG on the product side A + B → AB + energy

- CH4 + 3 O2 → CO2 + 2 H2O + energy

Endothermic: absorb energy; surrounding temp decreases; NRG on the reactant side

AB + energy→ A + B

- H2O(s) + energy → H2O (l)

Endothermic video http://www.youtube.com/watch?v=5RJLvQXce4A

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Law of Conservation of Mass/Matter/NRG

Matter is neither created nor destroyed in chemical reactions. In any chemical total numbers & kinds of atoms must remain unchanged in the reaction.

For chemical equations, this is called a balanced equation.

Charge, energy, mass, and # atoms are conserved (unchanged) in balanced reactions

4 H

2 O

4 H

2 O

4 g 32 g

36 g

How well did you focus? Partner How well did you focus? Partner Chat…Chat… Obtain a plastic baggie containing a substance. List 2 physical observations of the substance. Feel the outside of the baggie. Note the temperature.

Add some water to the baggie and seal mixing the two substances. List 2 physical observations of the substance. Feel the outside of the baggie. Note the temperature. When finished dispose of the baggie into the garbage.

SUMMARYSUMMARY:: All reactions involve heat (energy). The substance in the baggie is NH4Cl(s) .

When mixed with water, the solid dissolves forming NH4Cl(aq) . The reaction for this is as such:

NHNH44ClCl(s) (s) NH NH44+ +

(aq) (aq) + Cl+ Cl - -

(aq) (aq)

REFLECTIONREFLECTION: answer on a separate sheet of paper: answer on a separate sheet of paper1. Was the reaction endothermic or exothermic? Explain/give evidence to

support your answer.2. Would the term “heat” go on the reactant side or the product side of the

equation?3. According to Reference Table I, was your answer correct? What is the

amount of heat involved per 1 mole of substance produced? (Hint – look for this reaction)

4. In terms of entropy ( s), does it increase, decrease or RTS as the reaction proceeds from reactant to product? (Hint – look at phases)

5. Would this substance when placed in water conduct electricity? Support your answer.

When finished check your homework answers on the side overhead screen.

HH22OO

Chemical Change – chemical composition changes

Physical Change – chemical composition remains the same

Examples :Ripping, tearing, breakingBoiling, melting, freezing, vaporing a substance (a phase change)dissolving

Examples :Burning, rusting, oxidizingFlammable, explosive, reacting

Signs of a Chemical ReactionSigns of a Chemical ReactionEvolution of heat and light Evolution of heat and light Formation of a gasFormation of a gasFormation of a precipitate (solid)Formation of a precipitate (solid)Color changeColor change

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I II III IV VS.Panzarella

II. Balancing Equations

Chemical Reactions

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A. Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients to make #s equal.

Coefficient subscript = # of atoms

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

5. Double check atom balance!!!

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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

1 1

1 1

2 3

2

3

6

3

33 2

C. Balancing Example

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

2

2

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I II III IV VS.Panzarella

Chemical Reactions

III. Types of Chemical Reactions

Target: I can recognize the types of chemical reactions

TASK 1: Individual Read silently pages 37-40 in your review book. Complete the section on page 7 in your guide (PREFERABLY IN PENCIL) that is based on the reaction tag you have.

TASK 2 : Square OFF (teams of 4)nTaking turns, “teach” your type of reaction to the group so they can complete the reactions #1-4 on page 7. nGuide pg 8 - complete #1-20. Each person in the group should be prepared to explain and/or answer questions from the teacher upon completion.

TASK 3: Teacher Check for understanding & Reaction #5 : Combustion

TASK 4: Independent Homework: Review book pg 40 #59

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A. Combustion

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

the burning of any substance in O2 to produce heat

A + O2 B + H2O

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Na(s)+ O2(g)

C3H8(g)+ O2(g) 5 3 4

A. Combustion

Products: contain oxygen hydrocarbons form CO2 + H2O

CO2(g)+ H2O(g)

Na2O(s) 4 2

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B. Synthesis or Direct Combination

the combination of 2 or more substances to form a compound

only one product

A + B AB

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B. Synthesis

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

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Al(s)+ Cl2(g) AlCl3(s)2 3 2

B. Synthesis

Products: ionic - cancel charges

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C. Decomposition

a compound breaks down into 2 or more simpler substances

only one reactant

AB A + B

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C. Decomposition

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

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KBr(l) K(s) + Br2(l) 2 2

C. Decomposition

Products: binary - break into elements

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D. Single Replacement

one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-)

A + BC B + AC

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D. Single Replacement

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

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

D. Single Replacement

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

series-Table J)

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

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AB + CD AD + CB

E. Double Replacement

ions in two compounds “change partners” cation of one compound combines with

anion of the other

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E. Double Replacement

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

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

E. Double Replacement

Products: switch negative ions one product must be insoluble (check

solubility table)

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

2 2

I II III IV V

IV. Stoichiometry

• Study of QUANTITATIVE relationships between

substances to determine the PROPORTIONS in a chemical

relationship

The COEFFICIENTS of the FORMULAS in the balanced equation indicate the relative number of moles, molecules and volume (at STP) 0 OC & 1 atm

When working with chemical equations it is assumed that:

1. The reaction is a forward reaction (no side reactions).

2. The reaction goes to completion. 3. The reactants are completely used.

LIMITING REACTANT- LIMITS THE AMOUNT OF PRODUCT FORMED

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• Remember: Law of Conservation of Mass- • MASS and ENERGY are conserved in

EVERY chemical reaction (so is the charge)

1) Determining Mole Ratio (doesn’t give mass ratio)• Use the coefficient to get a mole

ratio:  

2 C2H6 + 7 O2 4 CO2 + 6 H2O 

• Mole ratio: • This means that 2 moles of C2H6

combine with 7 moles of O2 to produce 4 moles of CO2 and 6 moles of water.

2). Problem Solving using Stoichiometric calculations - start with the given (use factor label method or set up as a proportion)

I have 5 eggs. How many cookies can I make?

3/4 c. brown sugar1 tsp vanilla extract

2 eggs2 c. chocolate chips

Makes 5 dozen cookies.

2 1/4 c. flour1 tsp. baking soda

1 tsp. salt1 c. butter

3/4 c. sugar

5 eggs 5 doz.

2 eggs= 12.5 dozen cookies

Ratio of eggs to cookies

A) Mole-Mole and volume-volume Problems (gases only at STP)

REMEMBER moles and volume are directly related: 1 mol = 22.4 L

Example #1: mol-molHow many moles of water will be produced from the complete combustion of 3 moles of ethane (C2H6 )?

2 mol C2H6 3 mol C2H6

= 6 mol H2O

x mol H2O= 9 mol H2O

2 C2H6 + 7 O2 4 CO2 + 6 H2O? mol3 mol

EquationProblem

How many liters of ethane can be completely oxidized by a reaction with 63 liters of oxygen gas?

2 L C2H6 X L C2H6

= 7 L O2

63 L O2

= 18 L O2

2 C2H6 + 7 O2 4 CO2 + 6 H2O

? L 63 L

EquationProblem

Ex. #2 vol-vol

Ex #3: mol-molAssuming at STP, how many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen. (this is called the Haber Process)

1 mol N2

X mol N2

= 2 mol NH3

5.5 mol NH3

= 2.75 mol N2

N2 + 3 H2 2 NH3? mol .60 mol

Ex #4: vol –mol Using the above equation, how many liters of nitrogen are needed to produce 5.5 moles of NH3?

x 22.4 L = 61.6 L N2

1 mol N2

2 mol NH3 .60 mol NH3

= 1 mol N2 x mol N2

= .3 mol N2

Stoichiometry Steps1. Write a balanced equation.2. Identify known & unknown.3. Line up conversion factors.

Mole ratio - moles moles Molar mass - moles grams Molar volume - moles liters gas

Core step in all stoichiometry problems!!

• Mole ratio - moles moles

4. Check answer.

Conversion factors in stoich

Molar Mass(g/mol)

6.02 1023

particles/mol

MASSIN

GRAMSMOLES

NUMBEROF

PARTICLES

LITERSOF

SOLUTION

Molar Volume (22.4 L/mol)

LITERSOF GASAT STP

Molarity (mol/L)

Ex #1. How many grams of silver will be formed from 12.0 g of copper?

Cu + 2AgNO3 → 2Ag + Cu(NO3)2

12.0 g Cu x 1 mol Cu = .19 moles Cu 64 g/mol Cu

? g = ? mol

a. g-mol

B). Mass-Mass Problems (convert g→ mol→ mol→ g)

b. mol-mol ratio 1 mol Cu = 2 mol Ag = 10.5 mol Ag .19 mol Cu x mol Ag

c. mol-g 10.5 mol Ag x 108 g Ag = 1134 g Ag 1 mol Ag

Ex #2. What mass of silver nitrate is required to liberate 54 g of silver?

Cu + 2 AgNO3 → Cu(NO3) 2 + 2 Ag

54 g Ag x 1 mol Ag = .5 moles Ag 108 g/mol Ag

a. g-mol

B). Mass-Mass Problems (convert g→ mol→ mol→ g)

b. mol-mol ratio2 mol AgNO3 = 2 mol Ag = .5 mol AgNO3 X mol AgNO3 .5 mol Ag

c. mol-g.5 mol AgNO3 x 170 g AgNO3 = 85 g AgNO3

1 mol AgNO3

x g = ? mol

54 g = ? mol

3Wa4 + 12Ch + 16Ma 4Wa3Ch3Ma4

3 cups of water 12 tablespoons of chocolate 16 marshmallows Produce 4 servings of Hot Chocolate

Using the balanced equation and the factor label method determine the amount of water, chocolate and marshmallows needed to produce 1 serving.

Group Activity: Limiting Reactants

3Wa4 + 12Ch + 16Ma 4Wa3Ch3Ma4

1 serving x 1 serving x 3 c. water3 c. water = ¾ c water = ¾ c water

4 servings4 servings

1 serving x 1 serving x 12 T chocolate12 T chocolate = 3 T chocolate = 3 T chocolate

4 servings4 servings

1 serving x 1 serving x 16 marshmallows16 marshmallows = 4 marshmallows = 4 marshmallows

4 servings4 servings