AP Chemistry - Unit 4: Chemical Reactions

Physical Change

Change in properties but not composition

Chemical Change

Transformation into new substances with different compositions

What are indicators of chemical change

Precipitate, color change, production of gas, temperature change, and the release of light and gas

What is luster

Luster is how a mineral or material's surface looks when light reflects off it. It can be shiny like metal or not shiny like solid nonmetals

What is melting point

• The melting point is the temperature at which a solid turns into a liquid

• Ionic solids and metals have high melting points; covalent compounds have lower melting points

What is solubility

• Solubility is the ability of a solute to dissolve in a solvent and form a uniform mixture.

• Solubility depends on factors like temperature, pressure, and the nature of the solute and solvent.

• Ionic compounds and polar covalent solids are soluble in water

• Metals and nonpolar covalent solids are insoluble

What is conductivity

• Conductivity is a measure of how well a material conducts electricity.

• It indicates the ease with which electric charges can move through the material.

• Aqueous solutions of ionic compounds are conductors

• Aqueous solutions of polar covalent compounds are nonconductors

What is a reactant

• A reactant is a substance involved in a chemical reaction.

• Interact with other substances during the reaction.

• Consumed or changed during the reaction.

What is a product

• A product in chemistry refers to a substance formed from a chemical reaction.

• It can be the outcome of either synthesis or decomposition.

• Products are considered as new substances that are created during a chemical change.

What is a molecular equation

• Molecular equation: complete chemical formulas of reactants and products

• No indication of actual forms

• Shows all substances involved in the reaction

What is a complete ionic equation

• A complete ionic equation shows all ions in a reaction.

• It includes spectator ions.

• It represents the dissociation of soluble ionic compounds into constituent ions in a solution.

What is a net ionic equation

• A net ionic equation focuses on the species directly involved in a chemical reaction

• It excludes spectator ions, which do not undergo any chemical changes

• It shows only the essential chemical changes that occur during the reaction

What are the solubility rules

1. Most nitrate (NO3-) and acetate (CH3COO-) salts are soluble.

2. Most alkali metal (Group 1) and ammonium (NH4+) salts are soluble.

3. Most chloride (Cl-), bromide (Br-), and iodide (I-) salts are soluble, except for those of silver (Ag+), lead (Pb2+), and mercury (Hg2+).

4. Most sulfate (SO42-) salts are soluble, except for those of calcium (Ca2+), strontium (Sr2+), barium (Ba2+), lead (Pb2+), and silver (Ag+).

5. Most hydroxide (OH-) salts are insoluble, except for those of alkali metals (Group 1) and barium (Ba2+).

6. Most sulfide (S2-) salts are insoluble, except for those of alkali metals (Group 1), ammonium (NH4+), and calcium (Ca2+).

7. Strong acids are soluble (HCl, HBr, HI, HNO3, HClO4, H2SO4)

What is a ionic form

Ionic forms occur when atoms or molecules gain or lose electrons, forming charged ions. These ions can be positive (cations) or negative (anions).

How to write ionic equation

To write an ionic equation, follow these steps:

1. Start with the balanced molecular equation.

2. Break down all the soluble ionic compounds into their respective ions.

3. Write the ions as separate entities, indicating their charges.

4. Cancel out any spectator ions that appear on both sides of the equation.

5. Write the remaining ions as the ionic equation.

For example, let's consider the reaction between sodium chloride (NaCl) and silver nitrate (AgNO3):

Molecular equation: NaCl + AgNO3 → AgCl + NaNO3

Ionic equation: Na⁺ + Cl⁻ + Ag⁺ + NO3⁻ → AgCl + Na⁺ + NO3⁻

In this example, the sodium ion (Na⁺) and nitrate ion (NO3⁻) are spectator ions and can be canceled out. The resulting ionic equation is:

Ionic equation: Cl⁻ + Ag⁺ → AgCl

Remember to balance the equation and include the appropriate charges for each ion.

Physical changes typically involve breaking and/or forming

• Physical changes do not alter the substance's chemical composition.

• Physical changes involve breaking or forming chemical bonds or intermolecular forces.

• Examples of physical changes include:

  • Melting

  • Freezing

  • Boiling

  • Condensation

  • Dissolving

Chemical changes typically involve breaking and/or forming of

Chemical changes typically involve breaking and/or forming of chemical bonds.

What is stoichiometry

Stoichiometry is a branch of chemistry that uses balanced equations to calculate amounts of substances involved in chemical reactions.

What is a limiting reactant

A limiting reactant is the substance that is completely consumed in a chemical reaction.

How to determine limiting reactants

To determine the limiting reactant chemically, you need to compare the amounts of reactants given and their stoichiometric ratios.

1. Balance chemical equation

2. Convert the given amounts of reactants to moles using their molar masses.

3. Determine the mole ratio between the reactants based on the coefficients in the balanced equation.

4. Compare the mole ratios to identify the reactant that is present in the lower amount.

5. The reactant with the lower amount is the limiting reactant.

6. The lesser amount of the product is the true answer

What is a theoretical yield

• The theoretical yield is the amount of product calculated using the limiting reactant

• The amount of product that is obtained in the lab is the actual yield

• % yield = actual/theoretical x 100%

What is gas stoichiometry

• Gas stoichiometry applies the ideal gas law and mole concept.

• Determine ratios, volumes, and pressures of gases in chemical reactions.

• Helps to calculate the amounts of reactants and products in gas-phase reactions.

• Reactions occur in moles

What is titration

Titration is a lab technique to find the concentration of a substance in a solution.

What is a titrant

A titrant is a known concentration solution used in titration to determine the concentration of another solution.

What is an analyte

An analyte is the substance being analyzed in a lab or experiment, found in the sample being tested.

What is an equivalence point

An equivalence point is the point in a chemical reaction where the stoichiometrically equivalent amounts of reactants have completely reacted.

What is an endopoint

The indicator changes color so that you can tell the equivalence point has been reached

What are the five types of reactions

The five types of reactions are:

1. Combination or synthesis reaction

2. Decomposition reaction

3. Displacement or single replacement reaction

4. Double displacement or double replacement reaction

5. Combustion reaction

What is a neutralization reaction

A neutralization reaction is when an acid and a base react to form a salt and water. It involves the transfer of protons (H+) from the acid to the base, neutralizing their acidic and basic properties.

What is the Arrhenius concept

The Arrhenius concept explains acid-base reactions. Acids release H+ ions in water, while bases release OH- ions. When acids and bases combine, they form water and a salt.

What is the Brownsted-Lowry concept

• Acids are defined as proton donors.

• Bases are defined as proton acceptors.

• Acid-base reactions involve the transfer of protons between the acid and base.

• The Bronsted-Lowry concept explains the nature of acids and bases in terms of proton transfer.

What are the rules for determining oxidation numbers

The rules for determining oxidation numbers are as follows:

1. Element by itself is always zero.

2. The oxidation number of a monatomic ion is equal to its charge.

3. Oxygen, -2.

4. Hydrogen, +1.

5. The sum of oxidation numbers in a neutral compound is always zero.

6. The sum of oxidation numbers in a polyatomic ion is equal to its charge.

7. Group 1 elements (alkali metals), +1.

8. Group 2 elements (alkaline earth metals), +2.

9. Fluorine, -1

10. Halogens (Group 17), -1.

What is precipitation?

• It occurs when water vapor condenses and becomes too heavy to stay in the air.

• Reactions that result in the formation of an insoluble product are known as precipitation reactions.

What is the arrhenius concept?

• Acids release H+ ions in water

• Bases release OH- ions in water

What is the Bronsted-Lowry concept?

• The Bronsted-Lowry concept defines acids as proton donors and bases as proton acceptors.

• It includes substances that can donate or accept a proton (H+).

What is a conjugated base?

• A conjugated base is the result of the acid losing a hydrogen ion.

What is a conjugated acid?

• Conjugated acid forms when a base accepts a proton (H+) in a chemical reaction.

• It has one extra proton compared to its base.

What are redox reactions?

• Redox reactions involve electron transfer

• One element undergoes oxidation (loses electrons)

• Another species undergoes reduction (gains electrons)

• Consists of two half-reactions

• Require a reducing agent and an oxidizing agent

What is oxidation?

• It involves the loss of electrons by a substance.

• The oxidation state of the substance increases.

• Electron loss, increased positive charge, or bond formation are associated with oxidation reactions.

What is reduction?

• Reduction in chemistry involves the gain of electrons by an atom, ion, or molecule.

• It results in a decrease in the oxidation state of the species.

What is an oxidizing agent? (oxidant)

• An oxidizing agent causes oxidation by accepting electrons from another substance.

• It is typically a substance that undergoes reduction in the process.

What is a reducing agent? (reactant)

• A reducing agent donates electrons to another substance

• It causes the reduction of the substance it donates electrons to

• The reducing agent itself gets oxidized in the process

Method of Half-Reactions steps

1. Assign oxidation numbers to all elements; based on this, split the half-reactions of reduction and oxidation

2. For each, balance all elements except H and O

3. Balance oxygen by adding H2O to the opposite side

4. Balance hydrogen by adding H+ to the opposite side

5. Balance charges by adding e- to side with overall positive charge

6. Multiply each half-reaction by an integer so there are an equal number of e- in each

7. Add the half reactions; cancel any species; check final balance