Describing a Chemical Reaction

Indications of a Chemical Reaction

– Evolution of heat, light, and/or sound

– Production of a gas

– Formation of a precipitate

– Color change

ENERGY CHANGES IN REACTIONSENERGY CHANGES IN REACTIONS:: determined by determined by CHANGESCHANGES that occur that occur ININ chemical chemical BONDINGBONDING..

Chemical reactions Chemical reactions involve the involve the BREAKINGBREAKING of of chemicalchemical BONDSBONDS in in reactants and the reactants and the FORMATIONFORMATION of chemicalof chemical BONDSBONDS in products.in products.

Example: In the combustion of propane, the bonds in propane and oxygen molecules are Example: In the combustion of propane, the bonds in propane and oxygen molecules are broken, while the bonds in carbon dioxide and water molecules are formed.broken, while the bonds in carbon dioxide and water molecules are formed.

CC33HH88 + 5 O + 5 O22 ——> 3 CO ——> 3 CO22 + 4H + 4H220 + heat0 + heat

LAW OF CONSERVATION OF ENERGYLAW OF CONSERVATION OF ENERGY •In an exothermic reaction, the chemical energy of the In an exothermic reaction, the chemical energy of the reactants is reactants is CONVERTED INTO HEATCONVERTED INTO HEAT plus the chemical plus the chemical energy of the products.energy of the products.

•In an endothermic reaction, In an endothermic reaction, HEATHEAT plus the chemical energy plus the chemical energy of the reactantsof the reactants IS CONVERTED IS CONVERTED into the chemical energy of into the chemical energy of the products. the products.

In both cases, the total amount ofIn both cases, the total amount of ENERGY BEFORE AND AFTERENERGY BEFORE AND AFTER the the reactionreaction IS THE SAMEIS THE SAME..

Chemical Equations

• Reactants – the substances that exist before a chemical change (or reaction) takes place.

• Products – the new substance(s) that are formed during the chemical changes.

• CHEMICAL EQUATION indicates the reactants and products of a reaction.

REACTANTS PRODUCTS

Word Equations

• A WORD EQUATION describes chemical change using the names of the reactants and products. REMEMBER conservation of mass when converting to chemical equation

Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.

methane + oxygen carbon dioxide + water

Reactants Products

TYPES OF CHEMICAL REACTIONSTYPES OF CHEMICAL REACTIONS1. Oxidation-Reduction 1. Oxidation-Reduction (gain/loss of electrons)(gain/loss of electrons)

a. Synthesis – a. Synthesis – 2 or more substances form a new 2 or more substances form a new single substancesingle substance

b. Decomposition – b. Decomposition – One substance breaks down into One substance breaks down into simpler substancessimpler substances

c. Single-displacement – c. Single-displacement – A single element displaces A single element displaces another element from a compoundanother element from a compound

d. Combustion – d. Combustion – A compound reacts with OA compound reacts with O22 to form to form HH22O O

TYPES OF CHEMICAL REACTIONSTYPES OF CHEMICAL REACTIONS22. Double Displacement. Double Displacement (reactions where two elements or (reactions where two elements or groups of elements in two different compounds exchange groups of elements in two different compounds exchange places to form two new compounds)places to form two new compounds)

a. Precipitation – Ta. Precipitation – Two soluble substances form an wo soluble substances form an insoluble precipitateinsoluble precipitate

b. Acid-Base – b. Acid-Base – An acid reacts with a base to form a An acid reacts with a base to form a “salt” and water“salt” and water

c. Gas Evolution – c. Gas Evolution – A gas is formedA gas is formed

SYNTHESIS REACTIONSYNTHESIS REACTION:: two or more substances react two or more substances react

to to FORM A SINGLE SUBSTANCEFORM A SINGLE SUBSTANCE..

A + B → ABA + B → ABSOSO22 + O + O22 → SO → SO33

CO + OCO + O22 → CO → CO22

PP44OO1010 + H + H22O → HO → H33POPO44

CuBr + BrCuBr + Br22 → CuBr → CuBr22

DECOMPOSITION REACTIONDECOMPOSITION REACTION:: a compound a compound BREAKS BREAKS

DOWNDOWN into two or more simpler substances into two or more simpler substances..

AB → A + BAB → A + BHH22COCO33 → CO → CO2 2 + H+ H22OO

NCLNCL33 → N → N2 2 + CL+ CL22

NaHCONaHCO33 → CO → CO2 2 + Na+ Na22COCO33 + H + H22OO

SINGLE-REPLACEMENT REACTIONSINGLE-REPLACEMENT REACTION:: one element one element

TAKES THE PLACETAKES THE PLACE of another element in a compound of another element in a compound..

A + BC → B + ACA + BC → B + ACSiOSiO22 + Mg → Si + MgO + Mg → Si + MgO

Cu + HgNOCu + HgNO33 → Cu(NO → Cu(NO33))2 2 + Hg+ Hg

Li + HLi + H22O → LiOHO → LiOH + H+ H22

HH22SOSO44 + Ca → CaSO + Ca → CaSO4 4 + H+ H22

COMBUSTION REACTIONCOMBUSTION REACTION:: a substance a substance REACTS REACTS RAPIDLY WITH OXYGENRAPIDLY WITH OXYGEN, often producing heat, light, , often producing heat, light, COCO22 and water (overlaps with other types). and water (overlaps with other types).

CHCH44 + O + O22 → CO → CO22 + 2H + 2H22OOCC44HH1010 + O + O22 → CO → CO22 + H + H22OO

CC1010HH2222 + O + O22 → CO → CO22 + H + H22OO

CHCH44 + O + O22 → CO → CO22 + H + H22OO

DOUBLE-REPLACEMENT REACTIONDOUBLE-REPLACEMENT REACTION:: two different two different compounds compounds EXCHANGE POSITIVE IONSEXCHANGE POSITIVE IONS and form and form TWO TWO

NEW COMPOUNDSNEW COMPOUNDS..

AB + CD → AD + CBAB + CD → AD + CBCaClCaCl22 + K + K33POPO44 → Ca → Ca33(PO(PO44))22 + KCl + KCl

CaCOCaCO33 + HCl → H + HCl → H22COCO3 3 + CaCl+ CaCl22

AgSOAgSO44 + NH + NH44I → (NHI → (NH44))22SOSO44 + AgI + AgI

BaO + HNOBaO + HNO33 → Ba(NO → Ba(NO33))22 + H + H22OO

AlAl22(SO(SO44))33 + Ca(OH) + Ca(OH)22 → Al(OH) → Al(OH)33 + CaSO + CaSO44

Phase Symbols Used in Chemical Equations

“Yields”; indicates result of reaction

Used to indicate a reversible reaction

A reactant or product in the solid state; also used to indicate a precipitate

Alternative to (s), but used only to indicate a precipitate

A reactant or product in the liquid state

A reactant or product in an aqueous solution (dissolved in water)

A reactant or product in the gaseous state

(s)

(l)

(aq)

(g)

Phase Symbols Used in Chemical Equations

Alternative to (g), but used only to indicate a gaseous product

Reactants are heated

Pressure at which reaction is carried out, in this case 2 atm

Pressure at which reaction is carried out exceeds normalatmospheric pressure

Temperature at which reaction is carried out, in this case 0 oC

Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction

2 atm

pressure

0 oC

MnO2

CH4 + 2 O2 CO2 + 2 H2OMatter/Mass Conserved

Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

Timberlake, Chemistry 7th Edition, page 167

Balancing Chemical Equations

Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product.

Coefficients are used to balance, NOT subscripts

What is the relationship between conservation of mass andthe fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation?

Determine whether the following equation is balanced.

H2 + Cl2 HCl

Balancing Chemical Equations

1. Write a word equation for the reaction.

2. Write the chemical equation for all reactants and products, then use MINOH.

3. Balance metal coefficients first (M).

4. Next, look for polyatomic ions, and balance coefficients as a group (I).

4. Then, balance non-metal coefficients (N).

5. Balance O and H last (OH).

1) Write a word equation for the reaction.

Write a balanced equation for the reaction between iron (III)oxide and hydrogen to form iron and water

2) Write the correct formulas for all reactants and products.

3) Determine the coefficients that make the equation balance.

Iron (III) oxide + hydrogen iron + water

Fe2O3 + H2 (g) Fe + H2O

Fe2O3 + 3 H2 (g) 2 Fe + 3 H2O

1) Write a word equation for the reaction.

Write a balanced equation for the reaction between chlorineand sodium bromide to produce bromine and sodium chloride.

2) Write the correct formulas for all reactants and products.

3) Determine the coefficients that make the equation balance.

chlorine + sodium bromide bromine + sodium chloride

Cl2 (g) + NaBr Br2 (g) + NaCl

Cl2 (g) + 2 NaBr Br2 (g) + 2 NaCl

1) Write a word equation for the reaction.

2) Write the correct formulas for all reactants and products.

3) Determine the coefficients that make the equation balance.

aluminum sulfate + calcium chloride calcium sulfate

Al2(SO4)3 + CaCl2 CaSO4 (s) + AlCl3

Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate.

Al2(SO4)3 + 3 CaCl2 3 CaSO4 (s) + 2 AlCl3

+ aluminum chloride

Ca

Activity Series

Foiled again –Foiled again –Aluminum loses to CalciumAluminum loses to Calcium

Element Reactivity

LiRbKBaCaNaMgAlMnZnCrFeNiSnPbH2

CuHgAgPtAu

Halogen Reactivity

F2

Cl2Br2

I2

PrintableVersion

ofActivitySeries

PrintableVersion

ofActivitySeries

1) Write a word equation for the reaction.

Write a balanced equation for the reaction between nitrogentrihydride and oxygen to form nitrogen monoxide and water.

2) Write the correct formulas for all reactants and products.

3) Determine the coefficients that make the equation balance.

Nitrogen trihydride + oxygen nitrogen monoxide + water

NH3 + O2 (g) NO + H2O

4 NH3 + 5 O2 (g) 4 NO + 6 H2O

Cl

Cl

ClH

H

H

ClClCl

Cl HHH

H

H2 + Cl2 HCl H2 + Cl2 2 HCl

reactants products

H

Cl

reactants products

H

Cl

22

2 22 2

11

(unbalanced) (balanced)

Coefficients are used to balance, NOT subscripts