Modern Chemistry Chapter 8

Balancing equations step 3: balance the formula equation according to the law of conservation of mass

-Balance the different types of atoms one at a time - first balance the atoms of the elements that are combined and that appear only once on each side of the equation - balance polyatomic ions that appear on both sides of the equation as single units -balance H atoms and O atoms after atoms of all the other elements have been balanced

Decomposition rx's:

-single reactant will decompose -ACO3 2- becomes AO + CO2 -AOH: AO + H2O (metal oxide basic anhydrides) -AClO3: ACl + O2 -HXO: H2O + XO (nonmetal oxides acidic anhydrides) -AX: A + X

Information not provided by chemical equations:

1. An equation gives no indication that a reaction will occur -experimentation forms the basis for confirming that a particular chemical reaction will occur -a chemical equation can be written for a reaction that may not even take place. 2. Chemical equations give no information about the speed at which reactions occur 3. They also do not give info on how the bonding between atoms or ions changes during the reaction

Indications of a chemical reaction:

1. Evolution of energy as heat and light 2. Production of gas 3. The formation of precipitate 4. Color change

Active metals

A + HOH ---> AOH + H2

Chemical equation

A representation of a chemical reaction that represents the identities and relative molecular or molar amounts of the reactants and products in a chemical equation.

reversible reaction

A reversible reaction is a chemical reaction where the reactants form products that, in turn, react together to give the reactants back. Reversible reactions will reach an equilibrium point where the concentrations of the reactants and products will no longer change.

decomposition reaction

A rx in which a single compound undergoes a reaction that produce some two or more simpler substances AX ——> A + X Most only take place when energy (heat/electricity) is added

Coefficient

A small whole number that appears in front of a formula in a chemical equation; specifies the relative number of miles of each substance.

Precipitate

A solid that forms from a solution during a chemical reaction.

Reversible Reaction:

Achemical reaction in which the products re-form the original reactants (indicates by two opposite arrows) 3Fe +4H2O ➡️Fe3O4 + 4H2 ⬅️

Decomposition of metal Hydroxides

All metal hydroxides EXCEPT those containing group 1 metals decompose when heated to yield metal oxides and water metal hydroxide—>metal oxide + water MH —> mo + H2O Ca(OH)2 —> CaO + H2O Calcium hydroxide/calcium oxide + water

Displacement of a Metal in a Compound by Another Metal

Aluminum is more active than lead. When solid aluminum is placed in aqueous lead(II) nitrate, Pb(NO3)2, the aluminum replaces the lead. Solid lead and aqueous aluminum nitrate is formed. 2Al + 3Pb(NO3)2 --> 2Al (NO3)3

Metals with fixed charges

Aluminum, Al : 3+ Barium, Ba Cadmium, Cd Calcium, Ca: 2+ Cesium, Cs: Lithium, Li Magnesium,Mg Potassium, K Rubidium, Rb Silver, Ag Sodium, Na Strontium, Sr Zinc, Zn

Many single displacement reactions take place in

An aqueous solution

Word equation

An equation in which the reactants and products in a chemical reaction are represented by words (only qualitative description) methane + oxygen —> carbon dioxide+ water —> means yield Methane and oxygen react to yield carbon dioxide and water

The Diatomic molecules:

Br: liquid I: solid N: gas Cl: gas H: gas O: gas F: gas

Oxides of active metals, such as CaO, react with water to produce

Calcium hydroxide

Decomposition of Acids

Certain acids decompose into nonmetal oxides and water. nonmetal oxide + water H2SO4—> SO3 + H2O Sulfurous acid/ sulfur trioxide+water H2CO3—>CO2 + H2O Carbonic acid/carbon dioxide+water

Single displacement reactions

Chemical reactions where an element in a compound is replaced by another similar element A + BX—> AX + B Y + BX—> BX + Y

The decomposition of a substance by an electric current is called

Electrolysis

oxides of less active metals decompose into their elements when

HEATED

(Used in displacement reactions) An activity series is a:

List of elements organized according to the ease with which the elements undergo certain chemical reactions -For metals, greater activity means a greater LOSS of electrons -For nonmetals, greater activity means greater EASE of gaining electrons (forming negative ions)

Group 1 metals form oxides with the formula:

M2O

Group 2 metals form oxides with formula:

MO

Group 2 elements react w halogens to form IONIC compounds w/ formula:

MX2

Group 1 elements react w halogens to form IONIC compounds with the formula:

MX; m = metal, X = halogen Synthesis rx: 2Na + Cl2 —> 2NaCl

Decomposition of Metal Carbonates:

Metal carbonates wHen heated decompose into metal oxides and carbon dioxide metal carbonate —> metal oxide + carbon dioxide MC—> mo + CO2 CaCO3 —> CaO + CO2 Calcium carbonate —> calcium oxide + water

Oxides of active metals react with water to produce

Metal hydroxides

Displacement of Halogens

One halogen replaces another halogen in a compound. Each group 17 element can replace any element below it, but not any element above it 2KBr + Cl2 -->2KCl + Br2 chlorine can replace bromine in potassium bromide, but cannot replace fluorine in potassium fluoride Br2 + KCl --> no reaction Br can't replace chlorine

Many oxides of nonmetals in the upper right portion of the periodic table react with water to produce

Oxyacids Ex: SO2 reacts with water to produce Sulfurous Acid (main ingredient in acid rain)

Formula Equation

Represents the reactants and products of a chemical reaction by their symbols or formulas

Certain metal oxides and nonmetal oxides react with each other in synthesis reactions to form

Salts Ex: calcium sulfite is formed by the reaction of calcium oxide and sulfur oxide

Decomposition of binary compounds

Simplest kind of decomposition reactions

Catalyst

Substance that changes the rate of a chemical reaction but can be recovered unchanged

Sulfur forms reacts with oxygen to form:

Sulfur dioxide: SO2

types of chemical reactions

Synthesis Decomposition Single replacement Double replacement Combustion

Formation of a precipitate occurs when

The cations of one reactant combine with the anions of another reactant to form an insoluble or slightly soluble compound

Double displacement reactions

The ions of two compounds replace each other in an AQUEOUS solution to form two new compounds. One of the compounds is usually a precipitate and the other a molecular compound (usually water) AX + BY---> AY + BX

Displacement of Hydrogen in an Acid by a Metal

The more active metals react with certain acidic solutions, such as hydrochloric acid and dilute sulfuric acid, replacing the hydrogen in the acid. The reaction produces a salt (metal cmpd) and hydrogen gas. Mg + 2HCl ---> H2 + MgCl2 magnesium + hydrochloric acid---> hydrogen+ magnesium chloride.

Displacement of Hydrogen in water by a metal

The most-active metals, such as those in Group 1, react vigorously with water to produce metal hydroxides and hydrogen. -Group 1 metals produce metal hydroxides and hydrogen -Less-active metals, such as iron, react with steam to form a metal oxide and a hydrogen gas. 2Na + 2H2O---> 2NaOH + H2 sodium + water--->sodium hydroxide + hydrogen

synthesis/composition reaction

Two or more substances combine to form a new compound A + X —> AX

Decomposition of metal chlorates

When a metal chlorate is heated, it decomposes to produce a metal chloride and oxygen MChlorate—> MchlorIDE + Oxygen MCate—>MCide + O 2KClO3—> 2KCl + 3O2 Potassium chlorate/potassium chloride +Oxygen

🔺 Translate: 2HgO --> 2Hg + O2

When heated, solid mercury (II) oxide yields to liquid mercury and gaseous oxygen .

In some double displacement reactions

a very stable molecular compound (water) is formed. HCl reacts with an aqueous solution of sodium hydroxide to yeild aqueous sodium chloride and water.

In some double-displacement reactions, one of the products is

an insoluble gas

hydrocarbons or carbohydrates:

combustion rx's

Combustion reaction

reaction of an element or compound with oxygen to form an oxide and produce heat.

An activity series is useful because it allows a person to predict

whether or not a chemical reaction will take place.

Additional symbols used

⬆️: gas; ⬇️: precipitate

Significance of a Chemical Equation

1. The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products. H2 + Cl2—> 2HCl The equation indicates that 1 molecule of H reacts w 1 molecule of Cl to produce 2 molecules of HCl, giving the ratio of the smallest possible relative amounts of the rx's reactants and products. 2. The relative masses of the reactants and products of a chemical reaction can be determined from the reaction's coefficients. 2.02g H2 1 mol H2 *———— = 2.02 g H2 Mol H2 70.90g Cl2 1 mol Cl2 *———— = 70.90 g Cl2 Mol Cl2 36.46 g HCl 2 mol HCl*———— = 72.92 g HCl Mol HCl The chemical equation shows that 2.02 g of Hydrogen will react with 70.90 g of Chlorine to yield 72.92 g of HCl 3. The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction. -the equality of a chemical equation can be read from both sides (2 molecules of HCl break down to form 1 molecule of H and one molecule of Cl; similarly, 2 mol of HCl yield 1 mol of H 2.02 g and 1 mol Cl 70.90 g

Characteristics of Chemical Equations:

1. The equation must represent known facts. (All reactants and sources mist me identified) 2. The equation must contain the correct formulas for the reactants and products 3. The law of conservation of mass must be satisfied (the same number of atoms of each element must appear on both sides of the equation)