✍️ 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
AP Chemistry Self-Study and Homeschool
⏱️ 5 min read
October 25, 2020
Intermolecular Forces, IMFs, are attractions between entire molecules due to charge differences➕➖. (They typically tend to only affect the solid and liquid phases). Not only are IMFs weaker than bonds-attractive forces due to simultaneous attraction for electrons that exist between 2 nuclei- but they also depend on the type of particle in a sample of matter⚛️.
Three types of intermolecular forces exist between electrically neutral molecules: London dispersion forces, dipole-dipole attractions, and hydrogen bonding. And another kind of attractive force, ion-dipole is important in solutions.
London Dispersion Forces (LDFs) are the weakest type of IMFs and occur in all molecular samples.
They are the only types of forces to exist between two non-polar molecules and noble gases (solid or liquid form).
At any given time, one nonpolar molecule might have more electrons on one side than another side, making it polar. For that instant, the molecule would have a partial negative side and a partial positive side and it becomes a temporary dipole.
That temporary dipole (molecule) then induces a dipole on its neighboring molecule and there are LDF forces between the partial negative side of one molecular and the partial positive side of another molecule.
Here is a quick visual to sum up this idea of an LDF:
🌟Very important piece of information that is usually asked on the exam:
The strength of LDFs increase as the size of a molecule increases. This is because more electrons yield a stronger instantaneous dipole due to a more polarizable electron cloud. Polarizability is the ease at which an electron cloud could be distorted to give a dipole charge distribution.
Dipole-Dipole attractions occur due to the opposite partial charges that exist on the opposite ends of a dipole. Dipole-dipole attractions only occur in a sample of polar molecules and are slightly stronger than LDFs.
The dipoles in HCl lead to a positive side and a negative side that are attracted to each other
Image Courtesy of EMedicalPrep As you decrease the distance between the two dipoles, you strengthen the attraction and dipole-dipole interaction. Keep in mind, since these involve polar molecules, the element with the higher electronegativity (in this case Cl-) has the partial negative (δ−).
Image Courtesy of EMedicalPrep
As you decrease the distance between the two dipoles, you strengthen the attraction and dipole-dipole interaction. Keep in mind, since these involve polar molecules, the element with the higher electronegativity (in this case Cl-) has the partial negative (δ−).
This also means that the more polar the molecules, the greater the dipole-dipole attraction, which also relates to higher melting and boiling points.
The following question is from the 2018 AP Chemistry Examination. All credit to College Board.
The table above gives the molecular structures and boiling points for the compounds CS2 and COS. In terms of the types and relative strengths of all intermolecular forces in each compound, explain why the boiling point of CS2 (l) is higher than that of COS (l).
Sample Response: CS2 and COS both have London Dispersion Forces, but since COS is a polar molecule, it also exhibits dipole-dipole forces. However, the London Dispersion Forces in CS2 are so strong that they overpower the strength of both the LDFs and the dipole-dipole forces in COS. Therefore, CS2 has a higher boiling point.
Keep in mind🧠 that even though LDFs are the weakest forces, when they are strong and there are lots of them, they can overpower dipole-dipole forces. It all depends on the size of the molecule!
Hydrogen bonding is really everyone's favorite! It's the easiest to identify and the strongest, so they really stick in your mind throughout the whole year😊.
Hydrogen bonding (which is NOT a bond) is actually an unusually strong dipole-dipole attraction and only occurs when hydrogen is directly bonded to F, O, or N in a molecule. It occurs between these molecules because of their high electronegativity difference and small sizes, which leads to really really strong attractions.
💡Remember the acronym FON and that it only occurs in polar molecules!
The hydrogen bonded to the F, O or N is partially positively charged and is attracted to the neighboring unshared electrons on the F, O, or N.
Since these attractions are so so strong, the boiling points of molecules with hydrogen bonds are very high!
An example of a molecule that has hydrogen bonding is water (H2O). It is also seen in DNA🧬.
Let's clear a quick misconception before moving on:
On the AP Exam, you may be asked to draw a molecule with the proper orientation and create hydrogen bonding. Make sure you don't confuse😕 the difference between intermolecular and intramolecular, intermolecular is in between two molecules. Fiveable's here to help! 🎉
🎥Watch: AP Chemistry - Intermolecular Forces
Ion-Dipole attractions only occur in a mixture of an ionic compound with polar molecules. These attractions occur when ions are attracted to dipoles (ie: Dissolving NaCl in H2O). Overall, this IMF is stronger than dipole-dipole and H-Bonding.
Image Courtesy of ck12.org
Ion-Ion attractions occur in a sample of ionic compounds. This is the strongest type of attraction because there aren’t partial charges, but instead full charges on the ions. An example of an ion-ion interaction would be NaCl being attracted to other NaCl molecules to form a crystal lattice.
You may be wondering how we can determine the dominant IMF - well it’s quite easy with this simple diagram:
Image Courtesy of Pearson Education
🎥Watch: AP Chemistry - Halfway Unit 3 Review
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