CHEM131 Ch3 Molecules, Moles, & Chemical Equations

Chemical Formulae

Provide a concise way to represent chemical compounds

Chemical Equation

Builds upon chemical formulae to concisely represent a chemical reaction. Represents the transformation of one or more chemical species into new substances.

Reactants

Original materials, are written on the left-hand side of the equation.

Products

Newly formed compounds. Are written on the right-hand side of the equation.

S

Solid

l

Liquid

g

Gas

aq

Aqueous (substance dissolved in water)

Heat (Δ)

Thermal Reactions

Light (h)

Photochemical reactions

Law of conservation of matter

Matter is neither created nor destroyed. Chemical equations must obey this law; as in, the same number of atoms for each element must occur on both sides of the reaction arrow.

Stoichiometric Coefficients

Numbers used to balance a chemical equation.

Stoichiometry

The various quantitative relationships between reactants and products.

When balancing stoichiometric equations, do this:

Do not change species, do not use fractions, make sure you have the same number of atoms of each element on BOTH sides of the arrow.

Law reflected by this balanced equation: 2H₂(g) + O₂ (g) —> 2H₂O(g)

Conservation of MATTER. In this equation, the elements are neither created nor destroyed.

Microscopic

Visualizes the reactions between individual molecules.

Macroscopic

Visualizes reactions between bulk quantities.

Mole

Counting the large number of particles in a sample. 1 unit of this = 6.022×10²³ particles/ mole

Molar Mass

The sum of the molar masses of all the atoms in a compound.

Elemental Analysis

A laboratory procedure that determines the mass percentage of each element in a compound.

How to complete an Elemental Analysis

Assume a 100-gram sample size. Convert percents to mass. Ex: 16% C = 16 g C. Then, convert mass to moles using the molar mass. Divide by the smallest number of moles to get the mol-to-mol ratio for the empirical formula. If division results in small rational fractions, multiply ALL by an appropriate integer to get WHOLE NUMBERS.

Biomass

Refers to biological matter.

Chemical basis of biomass production

The photosynthetic formation of sugars.

Biofuels

Fuels dervied from biomass.

What form of energy is the primary result that is produced by a fuel cell?

Chemical energy released as electricity.

Aqueous Solution (reaction)

Reactions that occur in water are said to take place in this.

Solution

Homogeneous mixture of two or more substances.

Solvent

Solution component present in the greatest amount.

Solute

Solution component present in the lesser amount.

Concentration

A key piece of information for solutions. This is the relative amount of solute and solvent.

Concentrated

Solutions are this if many solute particles are present.

Dilute

Solutions are this if few solute particles are present.

For most concentrated solutions, which is present in greater amounts?

Solvent

Molarity (M)

The number of moles of solute per liter of solution. Molarity (M) = (moles of solute)/ (liter of solution) or (part/ whole) NOT (part/ part)

Dilution

The process in which solvent is added to a solution to decrease the concentration of the solute.

Dilution Formula

M_i*V_i=M_f*V_f

Soluble

Compounds which readily dissolve in water.

Insoluble

Compounds that do not readily dissolve in water.

Solubility Rules

Can predict solubility.

Electrolytes

Soluble compounds that conduct electricity when dissolved in water.

Weak Electrolytes

Dissociate partially into ions in solution.

Strong Electrolytes

Dissociate completely into ions in a solution.

Nonelectrolytes

Substances whose solutions do not conduct electricity.

Sugar

A nonelectrolyte—doesn’t conduct electricity when dissolved in water, as shown in the in-class demo.

Acetic Acid

From vinegar, this is a weak electrolyte, as shown in the demo when the lightbulb shined dimly.

NaCl

A strong electrolyte, this strongly conducts electricity when added to water, as shown by the in-class demo when the lightbulb shone brightly.

Nonelectrolytes

Covalently bonded material dissolved in water whose molecules remain intact. These do not conduct electricity.

Dissociation Reactions

Occur when ionic solids dissolve in water and decompose into their constituent ions. Ex: NaCl (s) → Na⁺ (aq) + Cl^- (aq) These compounds conduct electricity and are electrolytes.

Aqueous chemical reactions can be written as this

As a molecular equation. This shows the complete formula for each compound. Not all the species have to be molecules.

Total Ionic Equation

Dissociation of reactants and products is emphasized by writing this.

Spectator Ions

Ions not involved in the chemical reaction. When spectator ions are removed, the net ionic equation is created.

When HCl reacts with ammonia, what is/ are the spectator ion or ions?

Cl^-, because the reaction can be represented as H⁺ (aq) + Cl^- (aq) + NH₃ (aq) → NH₄⁺ + Cl^- (aq). All the species involved (other than Cl^-) are reacting to form a product.

What is left out when a net ionic equation is written?

Spectator ions are left out.

Acids

Substances that dissolve in water to produce H⁺ or H₃O⁺ ions. Examples: HCl, HNO₃, H₃PO₄, HCN

Bases

Substances that dissolve in water to produce OH^- ions. Examples: NaOH, Ca(OH)₂

Weak acids and weak bases

These partially dissociate in water. Use a two-way arrow to emphasize that the reaction does not proceed completely from left to right. This is called an equilibrium arrow. “⇌”

Neutralization

Mixing an acid and a base leads to this. The resulting solution is neither acidic nor basic. Ex: H₃O⁺ (aq) + OH^- (aq) → 2H₂O (l) + salt

Strong Electrolyte is true

What other property is true about a strong acid?

Both water and salt are products.

What are the products of a neutralization reaction?

Precipitation Reaction

When an aqueous reaction produces a solid, called the precipitate. Ex: Net ionic reaction for the precipitation of lead(II) iodide: Pb²⁺ (aq) + 2I^- (aq) → PbI₂ (s)

Carbon Sequestration

The process of removing carbon from the atmosphere, or from gases entering the atmosphere.