ChemistryNotes – Chemical Reactions and

Equations

Changes of Matter

• Chemical Change - When a substance is changed to a new form, but its molecules are different from before, and can’t be changed back.

• Describes its ability to change. Flammability, ability to react

• Examples: When substances are burned or chemically react. Burning paper, iron rusting, fireworks exploding.

Chemical change

• In a chemical change – the atoms are rearranged to form new substances with different chemical and physical properties

• The substances that undergo change in a chemical reaction are called reactants.

Chemical change

• The substances that undergo change in a chemical reaction are called reactants.

• The new substances formed by the reaction are called products

• Baking soda + vinegarReactants

• Bubbles• Carbon dioxide +

sodium acetateProducts

Chemical change

• The substances that undergo change in a chemical reaction are called reactants.

• The new substances formed by the reaction are called products

• NaHCO3 + H2C2H3O2

Reactants

• CO2 + NaC2H3O2

Products

Chemical Bonds – Chemical forces which hold atoms together and form complete

electrons shells

• Octet Rule – The outside shell holds a maximum of 8 electrons.

• Atoms will lose, gain, or share electrons to reach the octet number and become stable.

H2 – Hydrogen gas

O2 – Oxygen gas

NaCl – Table Salt

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Chemical Reactions and Equations

Chemical Reactions

• Chemical reactions involve changes in properties and changes in energy that you can observe.

• Examples of reactions:• 1) Color change (may

involve an indicator)• 2) Precipitate – a solid that

forms from two solutions• 3) Temperature change-

produces heat (exothermic) becomes colder (endothermic)

• 4) Production of gas – contents bubble or fizz

Chemical Equations - Show what takes place in chemical reactions . Matter and mass are the same before and after a

reaction

Reactants ProductsOriginal substances = What are produced What is used yields or

= equals

C + O2 = CO2 one atom Carbon 1 molecule 1 molecule

or 2 atoms carbon dioxide oxygen

Total atoms/elements on the left = equals to total number of atoms/elements on the right

2Na + Cl2 = 2NaClSodium Chlorine Sodium Chloride (Salt)2 Na 2 Cl 2 Na 2 Cl

Energy ReleaseExothermic - Gives off or releases energy (burning)Reactants Product + energyEndothermic – Absorbs energy ( ice pack, photosynthesis)Reactants + energy Product

Types of Reactions

1) Synthesis – One product from two reactants

H2 + O2 = H2O

Polymerization - Smaller molecules join to form one large molecule.

Types of Reactions

1) Synthesis – One product from two reactants

H2 + O2 = H2O Hydrogen + Oxygen = Water (Dihydrogen monoxide)

Polymerization - Smaller molecules join to form one large molecule.

Types of Reactions

1) Synthesis – One product from two reactants

H2 + O2 = H2O Hydrogen + Oxygen = Water (Dihydrogen monoxide)

C + O2 = CO2

endo- or exo- ?Polymerization - Smaller molecules join to form one

large molecule.

Types of Reactions

2) Decomposition – Two or more products from one reactant

CuO Cu + O2

Types of Reactions

2) Decomposition – Two or more products from one reactant

CuO Cu + O2Copper(II) Oxide Copper + Oxygen

Types of Reactions

3) Displacement – Two reactants form two new products

Single Displacement:

Cu + Ag(NO3) Ag + Cu(NO3)2

Types of Reactions

3) Displacement – Two reactants form two new products

Single Displacement:

Cu + Ag(NO3) Ag + Cu(NO3)2Copper(I) + Silver Nitrate Silver + Copper(I) Nitrate

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

KI + Pb(NO3) 2 K(NO3) + PbI2

CH4 + O2 CO2 + H2O

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

KI + Pb(NO3) 2 K(NO3) + PbI2Potassium + Lead Nitrate Potassium Nitrate + Lead

IodideIodide

CH4 + O2 CO2 + H2OCarbon + Oxygen Carbon Dioxide + Dihydrogentetrahydride

monoxide

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

K2Cr2O7 + Ca(OH)2 KOH + CaCr2O7

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

K2Cr2O7 + Ca(OH)2 KOH + CaCr2O7

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

K2Cr2O7 + Ca(OH)2 KOH + CaCr2O7Potassium Calcium Potassium Calcium dichromate hydroxide hydroxide dichromate

Chemical Equations

• Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction

Reactant + Reactant =Product + Product

Cu + Ag(NO3) =Copper + Silver Nitrate

Ag + Cu(NO3)2 Silver + Copper Nitrate

Stoichiometry: Balancing equations – Uses coefficients and

chemical formulas to show a balanced reaction• Law of Conservation of Mass - The amount of

matter before a reaction is equal to the amount after (same # and types of atoms)

H2O H2 + O2

Rules for equations

• 1) Formulas reacting are to the left of the arrow or equal sign

• 2) Formulas of molecules produced are on the right side

• 3)Total number of atoms used = total # produced. The number of each element or molecule on the left = # on the right

• 4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

H2O = H2 + O2

CuO = Cu + O2

Rules for equations

• 1) Formulas reacting are to the left of the arrow or equal sign

• 2) Formulas of molecules produced are on the right side

• 3)Total number of atoms used = total # produced. The number of each element or molecule on the left = # on the right

• 4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

H2O = H2 + O2 2-H,1-0 2-H,2-O

CuO = Cu + O2

Rules for equations

• 1) Formulas reacting are to the left of the arrow or equal sign

• 2) Formulas of molecules produced are on the right side

• 3)Total number of atoms used = total # produced. The number of each element or molecule on the left = # on the right

• 4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

H2O = H2 + O2 2-H,1-0 2-H,2-O

CuO = Cu + O2

1-Cu, 1-O 1-Cu,2-O

Rules for equations

3)Total number of atoms used = total # produced. The number of each element or molecule on

the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules or compounds cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

H2O = H2 + O2 2-H,1-0 2-H,2-O

CuO = Cu + O2

1-Cu, 1-O 1-Cu,2-O

Rules for equations

3)Total number of atoms used = total # produced. The number of each element or molecule on

the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

2H2O = 2H2 + O2 2-H,1-0=2-H,2-O4-H,2-O = 4-H,2-0CuO = Cu + O2

1-Cu, 1-O = 1-Cu,2-O

Rules for equations

3)Total number of atoms used = total # produced. The number of each element or molecule on

the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Reactants Products

2H2O = 2H2 + O2 2-H,1-0=2-H,2-O4-H,2-O = 4-H,2-02CuO = 2Cu + O2

1-Cu, 1-O = 1-Cu,2-O2-Cu, 2-O = 2-Cu,2-0

Rules for equations

3) Total number of atoms used = total # produced. The number of each

element or molecule on the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

5) All gases except Noble Gases VIII (He,Ne, Ar) occur in paired molecules: O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Nitrogen + Hydrogen =

Nitrogen trihydride (ammonia)

(g) = gas(l) = liquid(s) = solid(aq) = aqueous solution

Rules for equations

3) Total number of atoms used = total # produced. The number of each

element or molecule on the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

5) All gases except Noble Gases VIII (He,Ne, Ar) occur in paired molecules: O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Nitrogen + Hydrogen =N2 + H2 = NH3

Nitrogen trihydride (ammonia)

Hydrogen + Chlorine =

Hydrogen Chloride

Rules for equations

3) Total number of atoms used = total # produced. The number of each

element or molecule on the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

5) All gases except Noble Gases VIII (He,Ne, Ar) occur in paired molecules: O2, H2, N2 F2, Cl2, Br2, I2 - Halogens

Nitrogen + Hydrogen =N2 + H2 = NH3

Nitrogen trihydride (ammonia)

Hydrogen + Chlorine =H2 + Cl2 = HCl

Hydrogen Chloride

Rules for equations3) Total number of atoms used = total # produced. The number of each element or molecule on the left = # on the right4) Equations are balanced by changing coefficients. Subscripts of molecules cannot be changed.

• 5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2

F2, Cl2, Br2, I2 - Halogens

Pure metals are written as single elements.Silver = Ag Potassium = K

(g) = gas(l) = liquid(s) = solid(aq) = aqueous solution

Rules for equations

5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2

F2, Cl2, Br2, I2 - Halogens

Pure metals are written as single elements.Silver = Ag Potassium = K

• Oxygen (g) =

• Chlorine (g) =

• Bromine (l) =

• Copper (s) =

• Calcium (s) =

(g) = gas(l) = liquid(s) = solid(aq) = aqueous solution

Rules for equations

5) All gases except Noble Gases VIII (He, Ne, Ar) occur in paired molecules

O2, H2, N2

F2, Cl2, Br2, I2 - Halogens

Pure metals are written as single elements.Silver = Ag Potassium = K

• Oxygen (g) = O2

• Chlorine (g) = Cl2

• Bromine (l) = Br2

• Copper (s) = Cu

• Calcium (s) = Ca

(g) = gas(l) = liquid(s) = solid(aq) = aqueous solution

Rules for equations

5) All gases except Noble Gases VIII (He,Ne, Ar) occur in paired molecules: O2, H2, N2

F2, Cl2, Br2, I2 - HalogensPure metals are written as single elements.

Silver = Ag Potassium = K

6) Polyatomic ions in a displacement reaction can be counted as a group when counting atom/molecule #’s

Nitrogen + Hydrogen =Nitrogen trihydride (ammonia)

N2 + H2 = NH3

Hydrogen + Chlorine =Hydrogen ChlorideH2 + Cl2 = HCl

KI + Pb(NO3) 2 = K(NO3) + PbI2

K2Cr2O7 + Ca(OH)2 = KOH + CaCr2O7

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the

atoms

Copper(II) Oxide Copper + Oxygen

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the

atoms

Copper(II) Oxide Copper + OxygenCuO Cu + O2

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

CuO Cu + O2

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

Nitrogen + Hydrogen = Nitrogen trihydride(ammonia)

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

Nitrogen + Hydrogen = Nitrogen trihydride(ammonia)

N2 + H2 = NH3

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

Potassium + Chlorine = Potassium chloride

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

Potassium + Chlorine = Potassium chloride

K + Cl2 = KCl

Balancing Equations

• 1) Write the equation• 2) Count the atoms• 3) Use coefficients to balance the atoms

K2Cr2O7 + Ca(OH)2 = KOH + CaCr2O7

Conservation of Matter

• Conservation of Matter States that during a chemical reaction matter is neither created nor destroyed. The total mass of the reactants must equal the mass of the products

CuO = Cu + O2

Conservation of Matter

• Conservation of Matter States that during a chemical reaction matter is neither created nor destroyed. The total mass of the reactants must equal the mass of the products

2CuO = 2Cu + O2

The numbers placed in front of a chemical formula are called coefficients.

Balancing Equations

Mg + Cl2 = MgCl

N2 + H2 = NH3

Conservation of Matter

• Conservation of Matter States that during a chemical reaction matter is neither created nor destroyed. The total mass of the reactants must equal the mass of the products

CuO = Cu + O2

Conservation of Matter

• Conservation of Matter States that during a chemical reaction matter is neither created nor destroyed. The total mass of the reactants must equal the mass of the products

2CuO = 2Cu + O2

The numbers placed in front of a chemical formula are called coefficients.

Conservation of Matter

• Open system – matter can enter from or escape to the surroundings.

• Ex. – a burning match• Closed system – matter

is not allowed to enter or leave.

• Ex. – a sealed container

Energy and Reactions

• Activation energy – The minimum amount of energy needed to start a chemical reaction

4 factors that effect rates of reaction:

• 1) Surface area• 2) Temperature• 3) Concentration• 4) Presence of catalysts

or inhibitors

Rates of Chemical Reactions

• Concentration – The amount of substance in a given volume. Higher amounts increase reaction rates.

• Catalysts – Materials that increase reaction rates by lowering the activation energy

Rates of Chemical Reactions

• Catalysts – Materials that increase reaction rates by lowering the activation energy – Example: Enzymes –

Biological catalysts in cells that affect chemical reactions. Speed up reactions at lower temperatures.

Rates of Chemical Reactions

• Catalysts – Materials that increase reaction rates by lowering the activation energy – Example: Enzymes –

Biological catalysts in cells that affect chemical reactions. Speed up reactions at lower temperatures.

Rates of Chemical Reactions

• Inhibitors – A material used to slow down a reaction.– Example: Preservatives

in food

Understanding Fire

• Combustion: Fire is a result of a rapid reaction between oxygen and fuel.

• Fuel: A material that releases energy when it burns.– Anything that burns is

combustible, if it burns very rapidly it is flammable

Understanding Fire

• The Fire Triangle• 3 Things necessary to

start and maintain a fire:

1) Fuel2) Oxygen3) Heat