Ch. 4 - Compounds and Stoichiometry

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What is a compound?

A substance composed of two or more elements in a fixed proportion.

What is molecular weight?

The mass (in amu) of the constituent atoms in a compound as indicated by the molecular formula.

What is molar mass?

The mass of one mole (6.022 × 10²³ particles) of a compound, measured in grams per mole.

What is gram equivalent weight?

The mass of a substance that can donate one equivalent of the species of interest.

What is normality?

The ratio of equivalents per liter

related to molarity (mol/L) = multiplying molarity by the number of equivalents per mole of compound.

What are equivalents?

Moles of the species of interest, often seen in acid-base chemistry or redox reactions.

What does the law of constant composition state?

Any pure sample of a compound contains the same elements in the same mass ratio.

What is the empirical formula?

The smallest whole-number ratio of the elements in a compound.

What is the molecular formula?

Either the same as or a multiple of the empirical formula, giving the exact number of atoms of each element.

How do you calculate percent composition by mass?

Divide the mass of the individual element by the molar mass of the compound.

What are combination reactions?

Reactions where two or more reactants combine to form one product.

What are decomposition reactions?

Reactions where one reactant breaks down into two or more products.

What are combustion reactions?

Reactions where a fuel and an oxidant (usually oxygen) react

forming water and carbon dioxide (if the fuel is a hydrocarbon).

What are displacement reactions?

Reactions where one or more atoms/ions in a compound are replaced with those of another element.

What is the difference between single- and double-displacement reactions?

• Single-displacement: One ion is replaced with another element.

• Double-displacement: Elements from two compounds trade places to form two new compounds.

What are neutralization reactions?

Reactions where an acid reacts with a base to form a salt and usually water.

Why must chemical equations be balanced?

To perform stoichiometric calculations and ensure conservation of mass and charge.

What are the steps to balance a chemical equation?

1. Balance the least common atoms.

2. Balance more common atoms (like hydrogen and oxygen).

3. Balance charge, if necessary.

What is the limiting reagent?

The reactant consumed first in a reaction, limiting product formation.

What are excess reagents?

Reactants that remain after the limiting reagent is consumed.

What is theoretical yield?

The amount of product if all of the limiting reactant is consumed with no side reactions.

What is percent yield?

Percent yield = (Theoretical yield/Actual yield) ​× 100

How are ionic charges named for nonrepresentative elements?

Roman numerals denote ionic charge.

What do –ous and –ic endings indicate?

• –ous: Lesser charge.

• –ic: Greater charge.

What suffix do all monatomic anions have?

–ide.

How are oxyanions named?

• –ite: Lesser oxygen.

• –ate: Greater oxygen.

• Hypo–: Fewest oxygen.

• Per–: Most oxygen.

How are polyatomic ions with hydrogen named?

Use "hydrogen" or "bi–" for one hydrogen and "dihydrogen" for two

How do metals and nonmetals form ions?

• Metals: Form positive cations based on group number.

• Nonmetals: Form negative anions based on electrons needed to complete the octet.

What are electrolytes?

Substances that dissociate in solution to provide equivalents of ions.

What determines the strength of an electrolyte?

Its degree of dissociation or solvation in solution.