✍️ 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
August 23, 2020
As mentioned earlier, ionic interactions can produce brittle, hard solids that have high melting points. This is due to the ions being held in a 3D array, known as a crystal lattice.
The reason for this is that ions are attracted to their opposites, and so negative ions surround positive ones and vice versa.
It is important to note that particle diagrams for ionic substances look differently than molecular substances. Covalent substances are usually represented by a molecule while ionic substances are represented by a network of positive😊 and negative😞 ions.
The lattice structure can be explained by the strong electrostatic forces:
E = kQ1Q2/d
Q1, Q2 = charges on the particles
d = distance between centers
k = constant 8.99 x 109 J-m/C2
energy increases as charge increases or when distance between atoms decreases
💡Attractive forces between cations and anions are maximized in the lattice structure while repulsive forces are minimized.
In a lattice, electrons are stuck in place, or in other words, they are localized. This makes ionic solids very poor conductors of heat and electricity since there are no electrons moving around.
When ionic solids melt into liquids though, they do conduct heat and electricity. This is because the ions are free to move in the liquid phase. This applies to the aqueous phase as well.
Lattice Energy is the energy released when ions bond to form an ionic solid. Remember Coulomb's Law? It actually relates to lattice energy too; it's kind of everywhere.
To recall, Coulomb's Law states that the smaller the distance and the higher the charge, the stronger the attraction between two ions💪.
Let's ease into lattice energy...do you also remember how to find out which ionic compound would have a higher melting point? Let's review that, it'll help with lattice energy I promise!
Out of NaF and NaCl, which one has the higher melting point?
First, we would look at the charges of the ions. Here, they are both +1/-1, so charges can't have an effect on the differences in melting point. Then, we would look at which ions are smaller. Remembering the periodic trends, F- is much smaller than Cl-. Since it is smaller, it can be closer to the Na+ ion and increase the strength of attraction. Therefore, it takes more energy to break the bond, increasing the melting point.
If you still don't remember that process, you can review here!
Lattice energy depends on the same two concepts that you used in that question: charge and distance. Coulomb's Law directly relates to melting point and lattice energy so just remember:
Easy rule, right? Let's try a few out:
Which of the following compounds have a higher lattice energy?
NaF or NaCl
Since we already thought this question through, it's easy to tell that NaF has the higher lattice energy.
MgO or NaF
Charge first: Mg and O have a +2/-2 charge, while Na and F have a +1/-1 charge. You don't even have to check distance, MgO must have the higher lattice energy.
NaF or KCl
Since these ions are in the same groups, they have the same charge. We must remember the periodic trends and that the farther down in a group you go, the larger the ions get. Therefore, K+ and Cl- are larger than Na+ and F-. With the smaller size, NaF has the higher lattice energy.
LiCl or NaCl
Last one! Since Li+ is smaller, LiCl must have the higher lattice energy.
The following question is from the Advanced Placement YT Channel. All credit to them.
Answer the following questions related to Mg and Sr.
Write the complete ground state configuration for the ions Mg+2 and Sr+2.
Do you predict that the ionic radius of Sr+2 is larger or smaller in size than the ionic radius of Mg+2? Justify your answer in terms of atomic structure and the electron configuration of each ion.
The lattice energy of MgCl2(s) is equal to 2300 kJ/mol. Do you predict that the lattice energy of SrCl2(s) should be less than or greater than 2300 kJ/mol? Justify your answer in terms of Coulomb's law.
(a) Looking at the periodic table and remembering electron configuration, you should get:
You cannot leave the electron configurations of Mg and Sr as your final answer! Make sure you always answer what they are asking.
I originally wrote down the electron configurations of Mg and Sr and then took off two valence electrons to get the final electron configurations of Mg+2 and Sr+2.
(b) This question goes back to periodic trends. Which ion has more electrons and electron shells? Sr2+ does, so it has the larger ionic radius.
Sample Response: Sr+2 has a larger ionic radius than Mg+2 because it has more occupied electron shells. The valence electrons in Sr2+ are in the 4th energy level whereas the valence electrons in Mg2+ are in the 2nd energy level. Electrons in the 4th energy level are generally farther away from the nucleus, making the ion larger.
(c) Charges are the same, so size must be accountable for the difference in lattice energy.
Sample Response: Coulomb's law states that the higher the charges of the ions and the smaller the distance between the ions, the stronger the attraction and the higher the lattice energy. Although the charges of Mg and Sr are the same, Sr is a much larger ion due to its greater amount of occupied energy shells. Since it is larger, the distance between Sr+2 and the chlorine ions is greater than the distance between Mg+2 and the chlorine ions. Therefore, the lattice energy of SrCl2 (s) must be less than 2300 kJ/mol.
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