AP Chemistry - Unit 4 Chemical Reactions

Physical Change

Change in properties, but not a change in composition. Change in intermolecular forces. Examples: Changes in the phase of a substance (solid, liquid, gas) or formation/separation of mixtures.

Chemical Change

Substances are transformed into new substances, typically with different compositions. Bonds are broken and formed. Evidence: energy change/production of heat or light, formation of a precipitate, or color change. Example: combustion (fire), oxidation (rust).

Ions that are soluble in water

Na⁺, K⁺, NH₄⁺, NO₃^-

Molecular Equation

A balanced equation showing the complete chemical formulas of reactants and products

Complete Ionic Equation

A balanced equation with all soluble strong electrolytes shown as ions

Spectator Ions

Ions that stay the same on both sides of the complete ionic equation. These play no direct role in the reaction.

Net Ionic Equation

A balanced equation that includes only ions and molecules directly involved in the reaction

Representations of Reactions

The reaction indicates that for every two moles of H₂O₂ consumed, two moles of H₂O and one mole of O₂ will be produced

Excess Reactant

The reactant that remains upon completion of the reaction

Limiting Reactant

One reactant will be completely consumed during the chemical reaction, effectively limiting the amount of product(s) produced.

Dissociation of a salt

Can be argued as both a physical and chemical change. The breaking of the ionic bonds within the salt is a chemical change. The ion-dipole interaction between the water and the individual ions is a physical change.

Stoichiometry

The coefficients of the reaction indicate the mole ratio of the reactants consumed. The problem tells you how much of the reactant is present.

Same Coefficients, Different Quantities

If the coefficients are the same, the reactants are used at the same rate and the reactants with fewer moles will be limiting.

Different Coefficients, Same Quantities

If you are given the same amount of each reactant, the substance with the greater coefficient is used at a faster rate and is therefore the limiting reactant

Gas Laws

The pressure in the container is directly proportional to the moles of the gas, with the coefficients of the balanced equation representing the moles. If moles decrease pressure also decreases.

Molarity/Concentration formula

M=mol/liters

Mole to mole conversion formula

Mole given (wanted coefficient/given coefficient)

If the filter paper is still wet

The measured mass of the filter paper and the precipitate would be too high. Then the calculated moles would be too high. Then the calculated concentration would be too high.

Brønsted-Lowry Theory

Acid-Base reactions exchange protons, H⁺. The acid functions as the proton donor. The base functions as the proton acceptor.

Hydronium ion, H₃O⁺

The ion formed when water functions as a Brønsted-Lowry base.

Hydrogen ion, H⁺

The ion formed when water functions as a Brønsted-Lowry acid.

Hydroxide ion, OH^-

The ion formed when a base dissociates in water.

Base

Gains H⁺, forms conjugate acid

Acid

Loses H⁺, forms conjugate base

Amphoteric

A substance that can function as either an acid or a base

Amine groups, NH₂

H⁺ will be attracted to the amine groups converting NH₂ to NH₃⁺

Carboxyl groups, COOH

The electronegative nature of oxygen contributes to the release of the hydrogen ion, leaving the remainder of the molecule unchanged in the reaction. COOH turns into COO^-

Strong Acids

HCl, HBr, HI, HClO₄, H₂SO₄, HNO₃

Strong bases

Group one and group two (columns)

Oxidation Number

The charge of the ion or equals zero in a free element

Oxidation

An increase in oxidation due to the loss of electrons

Reduction

A decrease in oxidation due to the gaining of electrons

Half-reactions

Shows which substance is gaining or losing electrons

Writing Balanced Redox reactions from half-reactions

Use the least common multiple of the electrons in each half-reaction to make the electrons equal and cancel them out

Precipitation Reactions

Double replacement reaction, often in aqueous solution, resulting in the formation of a solid

Acid-Base Reactions

Also referred to as proton transfer reactions or neutralization reactions. These reactions produce water and a salt. Involve the exchange of a hydrogen ion, H⁺.

Oxidation-Reduction Reactions

Redox reactions involve the transfer of one or more electrons between reactants.

Standard Solution

One of known concentration, is combined with an unknown solution in order to determine the concentration of the unknown

Analyte

In the flask, the unknown solution

Titrant

Added through the burette, the standard solution

Equivalence Point

Where the analyte completely reacts with the titrant. Moles of titrant added is equal to the moles of analyte present in the flaskl.

End Point

When the indicator used changes color

pH Meter

Used to track the change in pH throughout the experiment.

Titration curve

Represents the data collected from the pH meter. Can be used to determine the equivalence point and several other factors about the analyte.