# 7.1: The Mole

• Mole: A group of atoms, molecules, or formula units that contains 6.02 x 10^23 of these items.

• The number of items in a mole is equal to 6.02 x 10^23.

• Named after Amedeo Avogadro, an Italian physicist.

• One mole of any element always contains Avogadro’s number of atoms.

• Formula Unit: The groups of ions represented by the formula of an ionic compound.

# 7.2: Molar Mass and Calculations

• Molar Mass: The quantity in grams that equals the atomic mass of an element.

• The molar mass of an element is useful to convert moles of an element to grams, or grams to moles.

## Calculating the Molar Mass of a Compound

Calculate the molar mass for lithium carbonate, Li2CO3, used to produce red color in fireworks.

• Step 1: Obtain the molar mass of each element.

• Step 2: Multiply each molar mass by the number of moles (subscript) in the formula.

• Step 3: Calculate the molar mass by adding the masses of the elements.

## Converting Moles of an Element to Grams

Silver metal is used in the manufacture of tableware, mirrors, jewelry, and dental alloys. If the design for a piece of jewelry requires 0.750 mole of silver, how many grams of silver are needed?

• Step 1: State the given and needed quantities.

• Step 2: Write a plan to convert moles to grams.

• Step 3: Determine the molar mass and write conversion factors.

• Step 4: Set up the problem to convert moles to grams.

## Converting the Mass of a Compound to Moles

A box of salt contains 737 g of Sodium Chloride (NaCl). How many moles of NaCl are present?

• Step 1: State the given and needed quantities.

• Step 2: Write a plan to convert grams to moles.

• Step 3: Determine the molar mass and write conversion factors.

• Step 4: Set up the problem to convert grams to moles.

# 7.3: Equations for Chemical Reactions

• Chemical Change: It occurs when a substance is converted into one or more new substances that have different formulas and different properties

• Chemical Reactions: These always involve chemical change because atoms of the reacting substances form new combinations with new properties.

• Chemical Equation: It tells us the materials we need and the products that will form.

• Here, the formulas of the reactants are written on the left of the arrow, and the formulas of the products are on the right

• When there are two or more formulas on the same side, they are separated by a plus (+) sign. The delta sign (∆) indicates that heat was used to start the reaction.

• Balanced Equations: These show the same number of atoms for each element in the reactants as well as in the products.

• Coefficients: The whole numbers in front of the formulas.

• Law of Conservation of Matter: States that matter cannot be created or destroyed during a chemical reaction.

### Balancing a Chemical Equation

The chemical reaction of methane, CH4, and oxygen gas, O2, produces carbon dioxide (CO2) and water (H2O). Write a balanced chemical equation for this reaction.

• Step 1: Write an equation using the correct formulas for the reactants and products.

• Step 2: Count the atoms of each element in the reactants and products.

• Step 3: Use coefficients to balance each element.

• By placing a coefficient of 2 in front of the formula for H2O, a total of 4 H atoms in the products is obtained.

• We can balance the O atoms on the reactant side by placing a coefficient of 2 in front of the formula O2. There are now 4 O atoms in both the reactants and products.

• Step 4: Check the final equation to confirm it is balanced.

• In the final equation, the numbers of atoms of C, H, and O are the same in both the reactants and the products. The equation is balanced.

• In a balanced chemical equation, the coefficients must be the lowest possible whole numbers. Suppose you had obtained the following for the balanced equation:

• To obtain coefficients that are the lowest whole numbers, we divide all the coefficients by 2.

# 7.4: Types of Reactions

• Combination Reactions: Reaction from two or more elements or compounds bond that forms one product.

• Decomposition Reactions: These occur when a reactant splits into two or simpler products.

• Replacement Reactions: The element in a compound is replaced by other elements.

• Single replacement reaction: A reacting element switches place with an element in the other reacting compound.

• Double replacement reaction: The positive ions in the reacting compounds switch places.

• Combustion Reactions: A carbon-containing compound, usually a fuel burns in oxygen from the air to produce carbon dioxide, water, and energy in the form of heat or flame.

# 7.5: Oxidation-Reduction Reactions

• Oxidation-Reduction Reactions

• Electrons are transferred from one substance to another.

• If one substance loses electrons, another substance must gain electrons.

• Oxidation: The loss of electrons.

• Reduction: The gain of electrons.

• In general, atoms of metals lose electrons to form positive ions, whereas nonmetals gain electrons to form negative ions.

• In the cells of the body, the oxidation of organic (carbon) compounds involves the transfer of hydrogen atoms, which are composed of electrons and protons.

• In many biochemical oxidation–reduction reactions, the transfer of hydrogen atoms is necessary for the production of energy in the cells.

# 7.6: Mole Relationships in Chemical Equations

• Law of Conservation of Mass: States that there is no change in the total mass of the substances reacting in a chemical reaction.

• In a balanced equation, the total mass of the reactants is equal to the total mass of the products.

• The coefficients in an equation describing the relationship between the moles of any two components are used to write mole–mole factors.

• When the number of moles for one substance is known, a mole–mole factor is used to find the moles of a different substance in the reaction.

# 7.7: Mass Calculations for Reactions

• When we have the balanced chemical equation for a reaction, we can use the mass of one of the substances (A) in the reaction to calculate the mass of another substance (B) in the reaction.

• The calculations require us to convert the mass of A to moles of A using the molar mass factor for A.

• Then we use the mole–mole factor that links substance A to substance B, which we obtain from the coefficients in the balanced equation.

# 7.8: Energy in Chemical Reactions

• Activation Energy: The amount of energy required to break the bonds between atoms of the reactants.

• Three Conditions Required for a Reaction to Occur

• Collision: The reactants must collide

• Orientation: The reactants must align properly to break and form bonds.

• Energy: The collision must provide the energy of activation.

• Heat of reaction: It is the difference between the energy of the reactants and the energy of the products.

• Exothermic Reaction: The energy of the products is lower than the energy of the reactants.

• Endothermic Reaction: The energy of the products is higher than that of the reactants.

• Rate of Reaction: It is measured by the amount of reactant used up, or the amount of product formed, in a certain period.

• Reactions with low activation energies go faster than reactions with high activation energies.

• Catalyst: It acts by providing an alternate pathway with a lower energy requirement.