(c) McGraw Hill Ryerson 2007

• Chemical reactions result in chemical changes.– Chemical changes occur when new substances

are created.– The original substance(s), called reactants,

change into new substance(s) called products.

See pages 202 - 203

(c) McGraw Hill Ryerson 2007 See pages 202 - 203

(c) McGraw Hill Ryerson 2007

• Chemical reactions can be written in different ways.

– A word equation:• Nitrogen monoxide + oxygen nitrogen dioxide

– A symbolic equation:• 22NO(gg) + O2(gg) 22NO2(gg)

STATE OF MATTERSTATE OF MATTER

- Letters indicate the state of each compound.

(aq) = aqueous/dissolved in water

(s) = solid

( ) = liquid

(g) = gas

COEFFICIENTSCOEFFICIENTS

- Indicates how many of each molecule there is.

-Ie: there are 2 molecules of NO.

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– No new matter is created or destroyedNo new matter is created or destroyed; atoms are just rearrangedrearranged as the atoms change partners change partners to form new compounds.

– If there are 3 atoms of oxygen in the reactants, there MUST be 33 atoms of oxygen in the products.

– Number of each atom in reactants = number of each Number of each atom in reactants = number of each atom in products.atom in products.

• The law of conservation of mass:– Mass of reactants = mass of products

• The simplest form of chemical equation is a word equation.– Potassium metal + oxygen gas potassium oxide

• A skeleton equation shows the formulas of the elements/compounds but NOT in the correct proportions

• K + O2 K2O

• A balanced chemical equation balanced chemical equation shows all atoms and the coefficientscoefficients tells us how many molecules (and atoms) there are.– Balancing ensures ensures that the number of each number of each

atom atom is the same on both sides same on both sides of the reaction arrow.

44K + O2 22K2O

K

K

K

K

K

K

K

K

O O O

O

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• Using the law of conservation of mass, we can count atoms to balance count atoms to balance the number of atoms in chemical equations.– Word equation: methane + oxygen water +

carbon dioxide

– Skeleton equation: CH4 + O2 H2O + CO2

• To balance the compounds, take note of how many

atoms of each element occur on each side of the

reaction arrow.

See Page 207

(c) McGraw Hill Ryerson 2007

Skeleton equation: CH4 + O2 H2O + CO2

Carbon = 11 Carbon = 11

Hydrogen = 44 Hydrogen = 22

Oxygen = 22 Oxygen = 33

Balanced equation: CH4 + 22O2 22H2O + CO2 Carbon = 11 Carbon = 11

Hydrogen = 44 Hydrogen = 44

Oxygen = 44 Oxygen = 44

The same number of atoms must be on

each side.

See Page 207

Balancing Equations

ReactantsReactants ProductsProducts

HH 22 22

hydrogen + oxygen water

OO22 HH22OOHH2 2 ++

OO 22 11

Balancing Equations

H2 + O2 H2O2

ReactantsReactants ProductsProducts

HH 22 22

OO 22 22

hydrogen + oxygen hydrogen peroxide

XYOU CANNOT CHANGE THE SUBSCRIPTS

Balancing Equations

H2 + O2 H2O

ReactantsReactants ProductsProducts

HH 22 22

OO 22 11

hydrogen + oxygen water

22

Balancing Equations

H2 + O2 H2O

ReactantsReactants ProductsProducts

HH 22 44

OO 22 22

hydrogen + oxygen water

22

Balancing Equations

22 H2 + O2 H2O

ReactantsReactants ProductsProducts

HH 44 44

OO 22 22

hydrogen + oxygen water

22(g) (g) (l)

(c) McGraw Hill Ryerson 2007

• Balance chemical equations by following these steps:– Trial and error will work but can be very inefficient.

• USE A TABLE USE A TABLE (write atoms underneath reactants and products)• If they look the same on both sides of the equation, treat treat

polyatomic ions polyatomic ions (such as SO42–) as a group as a group & balance them as

such.• If ‘OH’ and H2O are in the equation, write water as HOH. write water as HOH. • Balance one compound at a time Balance one compound at a time & rewrite the # of atoms rewrite the # of atoms in

the chart as things changeas things change.• Only add coefficientsOnly add coefficients; NEVER change subscripts!!!• If H and O H and O appear in more than one place, attempt to balance

them LASTLAST.– Balance everything that isn’t ‘H’ or ‘O’ 1st.– Balance the ‘H’s 2nd to last.– Balance the ‘O’s last.

– Always double-check Always double-check after you think you are finished.– CHECK YOUR ANSWERS!!!

See pages 209 - 211

• Balance the following:– Fe + Br2 FeBr3

– Sn(NO2)4 + K3PO4 KNO2 + Sn3 (PO4)4

– C2H6 + O2 CO2 + H2O

____Ba + ____H2O ____Ba(OH)2 + ____H2

 

 

 ____CO2 + ____H2O ____H2CO3

 

  

 

____Fe2O3 + ____C ____Fe + ____CO

 

  

 

____Fe + ____H2O ____H2 + ____Fe2O3

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• If you don’t transform your word into a skeleton equation properly, you won’t be able to balance the equation correctly.– Change chemical names into chemical

formulas. 4 types4 types:• Simple ionic compounds• Multivalent ionic compounds• Ionic compounds with polyatomic ions• Covalent compound

• Be careful of diatomic elements -- remember the special sevenspecial seven!! HH22, N, N22, O, O22, F, F22, Cl, Cl22, Br, Br22, I, I22

See page 208

(c) McGraw Hill Ryerson 2007 See page 208

Several common covalent molecules containing hydrogen have common names that you should know and MEMORIZE!! methane = CHmethane = CH44

glucose = Cglucose = C66HH1212OO66

ethane = Cethane = C22HH66

ammonia = NHammonia = NH33

(c) McGraw Hill Ryerson 2007 See page 208

Example #1: Word Equation: Solutions of lead nitrate react with potassium iodide to produce solid lead iodide and a solution of potassium nitrate.

Skeleton Equation: Pb(NO3)2(aq) + KI(aq) PbI2(s) + KNO3(aq)

Balanced Equation: Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

Example #2: Word Equation: Copper reacts with hydrogen nitrate to produce copper (II) nitrate plus hydrogen.

Skeleton Equation: Cu + H(NO3) Cu(NO3)2 + H2

Balanced Equation: Cu + 2H(NO3) Cu(NO3)2 + H2