Unit 4 Chemistry Honors Comprehensive Study Guide: Reactions and Stoichiometry

Element and Polyatomic Ion Naming: Mastery of the Periodic Table and the specific charges and names of polyatomic ions is required for both Honors-level chemistry naming and formula writing.
Formula Writing and Naming: This involves the ability to synthesize chemical names into correct chemical formulas (using subscripts to balance charges) and translating chemical formulas back into their systematic names (using Roman numerals for transition metals where applicable).
Naming Acids: Specialized rules apply to naming acids based on the suffix of the anion involved: * Anions ending in "-ide" become "hydro- -ic acid." * Anions ending in "-ate" become "-ic acid." * Anions ending in "-ite" become "-ous acid.

The Law of Conservation of Mass: In any chemical reaction, mass is neither created nor destroyed. In the context of chemistry, this means the total mass of the reactants must equal the total mass of the products. On an atomic level, the number of atoms for each element must be identical on both sides of the equation.
Balancing Chemical Equations: To satisfy the Law of Conservation of Mass, coefficients must be added to a chemical equation. All work should be shown to ensure that the atoms of each element are balanced between the reactant and product sides.
Translating Word Equations: This process involves converting a descriptive sentence (e.g., "aqueous sodium chloride reacts with silver nitrate…") into a symbolic chemical equation (e.g., $NaCl_{(aq)} + AgNO_{3(aq)} \rightarrow AgCl_{(s)} + NaNO_{3(aq)}$ ).
Symbols in Chemical Reactions: Knowledge and application of specific symbols are required to denote the physical state of substances and the conditions of the reaction: * $(s)$ : Solid * $(l)$ : Liquid * $(g)$ : Gas * $(aq)$ : Aqueous (dissolved in water) * $\rightarrow$ : Yields or produces (indicates the direction of the reaction) * $\Delta$ or "heat" over the arrow: Indicates heat is added to the reaction.

The Five Types of Chemical Reactions: 1. Synthesis (Combination): Two or more substances react to form a single new substance ( $A + B \rightarrow AB$ ). 2. Decomposition: A single compound breaks down into two or more simpler products ( $AB \rightarrow A + B$ ). 3. Single-Replacement: One element replaces a second element in a compound ( $A + BC \rightarrow AC + B$ ). 4. Double-Replacement: An exchange of positive ions between two compounds ( $AB + CD \rightarrow AD + CB$ ). 5. Combustion: An element or compound reacts with oxygen ( $O_2$ ), often producing energy in the form of heat or light; hydrocarbon combustion typically yields $CO_2$ and $H_2O$ .
Predicting Products: Given only the reactants, one must be able to determine the reaction type and use valence rules to correctly predict the resulting products.
The Activity Series: This list of elements organized by reactivity is used specifically for Single-Replacement reactions. A reaction will only occur (proceed) if the standalone element is more reactive (higher on the list) than the element it is attempting to replace within the compound.

Defining Stoichiometry: Stoichiometry is the quantitative study of relationships between reactants and products in a chemical reaction. For a non-chemist, it can be explained as the "recipe" of chemistry, allowing us to calculate exactly how much of a reactant is needed to produce a specific amount of product based on balanced equations.
Mole Ratios: These are derived from the coefficients of a balanced chemical equation. They serve as conversion factors to bridge the gap between different substances in a reaction (e.g., in the reaction $2H_2 + O_2 \rightarrow 2H_2O$ , the ratio of $H_2$ to $O_2$ is $2:1$ ).

Calculated Problem Types: * Mole-Mole: Converting moles of one substance to moles of another using the mole ratio. * Mass-Mass: Converting grams of a reactant to grams of a product (Gram A $\rightarrow$ Moles A $\rightarrow$ Moles B $\rightarrow$ Grams B). * Volume-Volume: Calculations involving gases at Standard Temperature and Pressure (STP), utilizing the molar volume constant of $22.4\,L\,mol^{-1}$ . * Mixed Versions: Problems that combine units, such as Mass-Volume or involving number of particles (molecules) using Avogadro’s number ( $6.02 \times 10^{23}$ ).
Precision and Standards: All work must be labeled properly with units and chemical formulas. Answers must be expressed using the correct number of significant figures (sig figs) based on the measurements provided in the problem.

Molarity Definition and Equation: Molarity ( $M$ ) is a measure of concentration defined as the number of moles of solute per liter of solution: $M = \frac{\text{moles of solute}}{\text{Liters of solution}}$
Executing Molarity Calculations: Ability to solve for any single variable (Volume, Mass, Moles, or Molarity) when provided with at least two of the other pieces of information.
Solute vs. Solvent: * Solute: The substance that is being dissolved (usually present in a smaller amount). * Solvent: The dissolving medium (usually present in a larger amount, like water in aqueous solutions).
Dilutions: The formula used to determine how to reduce the concentration of a solution by adding more solvent is: $M_1V_1 = M_2V_2$
Solubility Charts: Used to determine the state of matter of a compound in a double-replacement reaction. If a compound is insoluble according to the chart, it is labeled as a solid $(s)$ , indicating a precipitate has formed.

Limiting Reactant (Reagent): The reactant that is completely consumed in a reaction, thereby determining the maximum amount of product that can be formed.
Excess Reactant (Reagent): The reactant that remains after the limiting reactant is used up.
Calculation Process: To find the amount of product, one must first identify the limiting reactant by performing stoichiometry for each reactant. Once the limiting reactant is identified, it is used to calculate the theoretical amount of product and the remaining amount of the excess reactant.
Theoretical vs. Actual Yield: * Theoretical Yield: The maximum amount of product that can be produced as calculated via stoichiometry. * Actual Yield: The amount of product actually measured or obtained from an experiment in a laboratory setting.
Percent Yield: A measure of the efficiency of a reaction, calculated using the formula: $\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$

Percent Composition: The percent by mass of each element in a compound, calculated as: $\% \text{ mass of element} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$
Molecular vs. Empirical Formulas: * Empirical Formula: The lowest whole-number ratio of atoms of the elements in a compound. * Molecular Formula: The actual number of atoms of each element in a molecule (can be the same as or a multiple of the empirical formula).
Determining Empirical Formulas: Calculated by converting the mass (or mass percent) of each element to moles, then dividing each mole value by the smallest number of moles to find the whole-number subscripts.
Determining Molecular Formulas: Found by dividing the molar mass of the actual compound by the molar mass of the empirical formula to find a multiplier ( $n$ ), then multiplying the empirical subscripts by that value.