Unit 07 Notes (Ch.8 in textbook)

Unit 07 Notes(Ch.8 in textbook)

Chemical Reactions

Additional vocabulary:

Acid-Base Reactions - Also called a neutralization reaction; occurs when an acid reacts with a base. They are considered one type of double-replacement reaction. Products will be a salt and H2O.

Precipitation Reactions – Occurs when two soluble ionic compounds react to form an insoluble product, the precipitate. Precipitates form when the electrostatic force of attraction between the ions is greater than the tendency of the ions to stay in solution. They are common in both nature and industrial processes. A type of double-replacement reaction.

Phlogiston - A hypothetical substance formerly thought to be a volatile constituent of all combustible substances, released as flame in combustion.

Father of Mother of Modern ChemistryBoth lived during 18 th century

Antoine Lavoisier – father of modern chemistry Lots of research on combustion Disproved the theory of phlogiston

Marie-Ann Lavoisier – mother of modern chemistry Lab assistant to her husband Collaborator with her husband

A substance that undergoes a reaction is called a __________.

Reactants are written on the left of the arrow These will be the things you start with

When reactants undergo a chemical change, each

new substance formed is called a ___________. Products are written on the right of the arrow These are the things that you produce

Chemical Equations

chemical equations—use chemical formulas and an arrow to separate reactants from products

Fe + O2 → Fe2O3

skeleton equation—shows just the formulas; does not show the relative amounts of reactants and products used in the reaction

States of Matter and Symbols

Use symbol to show the state of matter (s) __________ (l) __________ (g) __________ (aq) __________ (substance dissolved in

water)

Fe (s) + O2 (g) →Fe2O3 (s)

Use of catalysts

many times, a catalyst is employed in a reaction

catalyst—speeds up the rate of reaction but is not used up in the reaction

(is written above the arrow in equation)

MnO2

2H2O2(aq) 2H2O(l) + O2(g)

Diatomic molecules Seven elements normally exist as diatomic

molecules—these will always be written as X2 when writing equations

H2

O2

N2

F2

Cl2 Br2

I2

In order to write equations you MUST remember your diatomic elements…

In a chemical equation the Law of conservation of matter MUST be observed!

This means the # of atoms of reactants = the # of atoms of products

What you start with has to equal what you end with

Balancing Chemical Equations unbalanced equation—an equation

that does not indicate the quantity of the reactants needed to make the products

balanced equation—gives the correct quantity of each reactant and product—each side of the equation has the same number of atoms of each element

coefficient—numbers placed in front of the symbols

1. Write the symbols for the reaction2. Count the number of atoms of each element of

the reactants. 3. Count the number of atoms of each element of

the products.4. Add / Change the coefficient to make the

numbers of each element equal.5. YOU CAN NEVER CHANGE A SUBSCRIPT !6. Write the coefficients in the lowest possible

ratio.7. Check your work.

Steps for Balancing Chemical Equations

Types of Reactions There are 5 major classifications of reactions:

Synthesis (or Combination) A + B AB

Decomposition AB A + B

Combustion A + O2(g) AO2

Single Replacement A + BC AC + B

Double Replacement AB + CD AD + CB

Flash cards:

Using the piece of paper given to you, write the name of each reaction type in a separate box. On the back side of the paper, write the sample equation on the corresponding area for each reaction type. As you have time, cut out the cards for studying.

Examples of Synthesis Reactions Metal + Nonmetal 2Na+ Cl2 2 NaCl

Two nonmetals S + O2 SO2

Nonmetal oxide + water acid SO2 + H2O H2SO3

Metal oxide + water base CaO + H2O Ca(OH)2

Example of Decomposition ReactionsCaCO3 CaO + CO2

Examples of Combustion Reactions2Mg + O2 2 MgO

C3H8 + 5O2 3CO2 + 4H2O

Single Replacement Reactions Also called Single Displacement Rxn.Example: Cu + 2AgNO3 2 Ag + Cu(NO3)2

MetalsWhether or not one metal will replace another can be

determined by consulting the Activity Series of Metals. A reactive metal will replace any metal BELOW it in the activity series.

In order for the reaction to occur, the lone element must be above the element in the compound

Otherwise…NO REACTION

Will the following reactions occur? If so, complete and balance the reaction.

Ag + Cu(NO3)2

Mg + AlCl3

Nonmetals A nonmetal can also displace another nonmetal from a

compound. This replacement is usually limited to the halogens (group 7A) and the reactivity decreases as you go down the periodic table.

Will the following reactions occur? If so, complete and balance the reaction.

Br2 + MgCl2

F2 + MgCl2

Double Replacement Reactions Also called Double Displacement Reaction Anions of two different compounds switch places,

forming two new compounds.

Generally occur between two ionic compounds in aqueous solution and usually form a

precipitate, gas, or molecular compound

Example: Na2CO3 + 2AgNO3 2NaNO3 + Ag2CO3