⏱️ October 15, 2020
From electronic devices📱 to fizzy soda🥤, our world runs on chemical reactions. So what happens in chemical reactions? In a simplified definition, specific interactions with molecules result in the rearrangement of atoms to create new molecules. However, this magic✨ has restrictions, as will be discussed in the next sections.
There are two types of changes in chemistry: physical changes and chemical changes.
A physical change is one that changes an object, but does not change the chemical structure. For example, you may boil water into steam, but H2O stays H2O💧 during that process. Similarly, shredding paper would be an example of a physical change. Paper may change from a piece to shreds, but it stays "paper"📄.
However, chemical changes, as the name implies, ends with a brand new product. For example, if you leave iron out for too long, it rusts. Rust is a chemical reaction between iron (Fe) and oxygen in the air (O2) to form rust (iron oxide, Fe2O3). Key marks of a chemical change are things like gas production♨️, color changes🔴🔵, odors👃, etc. Another example of a chemical change is mixing baking soda (NaHCO3) with vinegar (CH3COOH) to form carbon dioxide and other products. Chemical changes are the focus of AP Chemistry, and are described using chemical reactions.
🧠There are five main types of reactions: synthesis, decomposition, combustion, single replacement, and double replacement. While we will go over these in later sections, let’s do a brief overview for each type:
Synthesis reactions are the easiest type to understand. Essentially, a synthesis reaction sees two reactants fuse to form products in the form A + B --> AB, where A, B, and AB are arbitrary.
For example: 2Na + Cl2 → 2NaCl is a synthesis reaction, as it sees two reactants, Na and Cl2, become one product - NaCl.
The Synthesis of Sodium Chloride from Sodium Metal and Chlorine Gas
Decomposition reactions are the exact opposite - one reactant decomposes into 2 or more products. This can be represented by the general equation: AB → A + B. For example, hydrogen peroxide decomposes into hydrogen gas and water in the reaction 2H2 + O2 → 2H2O + H2.
The Elephant's Toothpaste: A violent reaction that is caused by a speeding up of the decomposition of hydrogen peroxide using a catalyst
A combustion reaction is a special type of reaction involving organic molecules, which are molecules that are carbon based. A special class of organic molecules are called hydrocarbons, since they only have hydrogen and carbon. When in the presence of heat and oxygen, hydrocarbons combust, or burn, which is really just the energy being released from a chemical reaction!
This chemical reaction sees a hydrocarbon being combusted into oxygen and carbon dioxide. For example, CH4 + 2O2 → CO2 + 2H2O is the combustion of methane (CH4). This definition of combustion is why oxygen is necessary for fires to start.
Combustion reactions always follow this format: Hydrocarbon + Oxygen = Carbon Dioxide + Water
The Methane Molecule - Image Courtesy of world of molecules
Single replacement reactions occur when you have a compound reacting with an element. The general form is AB + C --> AC + B. The most common form of a single replacement reaction is one called a redox reaction, where electrons are transferred between atoms. An example is 3Mg + 2AlCl3 --> 3MgCl2 + 2Al.
Single = one, replacement = an switch. One element switches places with another. Only one switch takes place.
The most common type of reaction is a double replacement, with the general form AB + CD --> AC + BD. For example, if you mix an acid and a base, you get a reaction that forms water and a salt. A formula example would be HCl + NaOH -> NaCl + H2O. These reactions are the majority of the reactions you'll see in AP Chemistry, so get used to them!
Double = two, replacement = switch. Two elements switch places with another. Here, two switches take place.
Identify what each of the following reactions are:
Zn + 2HCl → ZnCl2 + H2
2C8H18 + 25O2 → 16CO2 + 18H2O
2H2O → 2H2 + O2
AgNO3 + NaCl → AgCl + NaNO3
2Ni2O3 → 4Ni + 3O2
2Na + Cl2 → 2NaCl
Cl2 + 2NaBr → 2NaCl + Br2
BaCl2 + Na2SO4 → BaSO4 + 2 NaCl
C3H8 + 5O2 → 3CO2 + 4H2O
These reactions are just the basics. Once we dive deeper into the unit, we'll go over three important reactions:
🎥 Watch: AP Chemistry - Introduction to Chemical Reactions
✍️ Free Response Questions
AP Chemistry Free Response Questions
⚛️ Unit 1: Atomic Structure and Properties
1.1Moles and Molar Mass
1.2Mass Spectroscopy of Elements
1.3Elemental Composition of Pure Substances
1.4Composition of Mixtures
1.5Atomic Structure and Electron Configurations
1.6Photoelectron Spectroscopy & Graph Interp.
🤓 Unit 2: Molecular and Ionic Compound Structures and Properties
2.0Unit 2 Overview: Molecular and Ionic Bonding
2.1Types of Chemical Bonds
2.2Intramolecular Force and Potential Energy
2.3Ionic Bonding and Ionic Solids
2.4Metallic Bonding and Alloys
2.5Lewis Dot Diagrams
2.6Resonance and Formal Charge
🌀 Unit 3: Intermolecular Forces and Properties
3.0Unit 3 Overview: Intermolecular Forces and Properties
3.2Properties of Solids
3.3Solids, Liquids, and Gases
3.4The Ideal Gas Law
3.5The Kinetic Molecular Theory of Gases
3.6Deviations from the Ideal Gas Law
3.7Mixtures and Solutions
3.8Representations of Solutions
3.9Separation of Solids/Mixtures
3.10Solubility and Solubility Rules
3.11Spectroscopy and the Electromagnetic Spectrum
3.12Quantum Mechanics and the Photoelectric Effect
🧪 Unit 4: Chemical Reactions
4.0Unit 4 Overview: Chemical Reactions
4.1Recognizing Chemical Reactions
4.2Net Ionic Equations
4.4Physical vs. Chemical Changes
4.5Stoichiometry & Calculations
4.6Titrations - Intro and Calculations
4.8Intro to Acid-Base Neutralization Reactions
👟 Unit 5: Kinetics
5.0Unit 5 Overview: Kinetics
5.1Defining Rate of Reaction
5.2Introduction to Rate Laws
5.3Rate and Concentration Change
5.4Writing Rate Laws
5.5Collision Model of Kinetics
5.6Reaction Energy and Graphs w/ Energy
5.7Reaction Mechanisms and Elementary Steps
5.8Writing Rate Laws Using Mechanisms
🔥 Unit 6: Thermodynamics
6.0 Unit 6 Overview: Thermochemistry and Reaction Thermodynamics
6.1Endothermic Processes vs. Exothermic Processes
6.2Energy Diagrams of Reactions
6.3Kinetic Energy, Heat Transfer, and Thermal Equilibrium
6.4Heat Capacity and Coffee-Cup Calorimetry
6.5Phase Changes and Energy
6.6Introduction to Enthalpy of Reaction
6.7Bond Enthalpy and Bond Dissociation Energy
6.8Enthalpies of Formation
⚖️ Unit 7: Equilibrium
🍊 Unit 8: Acids and Bases
8.0Unit 8 Overview: Acids and Bases
8.1Introduction to Acids and Bases
Unit 9: Applications of Thermodynamics
🤺 AP Chemistry Essentials
🧐 Multiple Choice Questions
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