✍️ 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
⏱️ 3 min read
August 22, 2020
Enthalpy, or heat energy, is represented by ΔH (Δ is the delta sign, which means change). If there is a negative change in energy, or -ΔH, an exothermic reaction is taking place and energy is released🔥 from the system to the surroundings. If there is a positive change in energy, or +ΔH, an endothermic reaction is taking place and energy is absorbed into the system from the surroundings.
The basics of exothermic and endothermic reactions is understanding phase changes and which process is taking place.
For example, is H2O(s) →H2O(l) an endothermic process or an exothermic process?
Ice🧊 is melting into liquid water in this reaction but you should be thinking, "Does this involve absorbing energy or releasing energy? Is heat needed to melt the ice?"
Yes! In order to melt ice, heat is needed. Think about it, if you hold an ice cube in your hand, it'll melt because of your body warmth. Therefore, heat is going into the system, heat is being absorbed by the water, and melting is an endothermic process.
What about H2O(g) → H2O(l)?
This is how I would think about it: condensation is the opposite of boiling, right? Boiling requires energy/heat to happen, that's why it takes forever for water to boil🍜. Well, if boiling requires energy to happen and condensation is the opposite, condensation must be an exothermic process. Therefore, that reaction releases energy (from the system out to the surroundings).
|Melting||Solid → Liquid||Endothermic|
|Vaporization / Boiling||Liquid → Gas||Endothermic|
|Sublimation||Solid → Gas||Endothermic|
|Condensation||Gas → Liquid||Exothermic|
|Freezing||Liquid → Solid||Exothermic|
|Deposition||Gas → Solid||Exothermic|
Physical or chemical processes can be described through energy diagrams. As mentioned before, reactions can be categorized as endothermic or exothermic processes. The energy diagrams below show what should be known for the test.
Image Courtesy of Pinterest
Before looking at the specifics of each, you should be aware of a few terms:
PEreactants - The potential energy of the reactants
PEproducts - The potential energy of the products
Activation Energy - Energy necessary for the reaction to occur
Activated Complex - The maximum point of energy, where the reactants turn into the products and the reaction occurs.
In the graph for an exothermic reaction, you can see that the products have a lower potential energy, implying that energy has been released from the system. This further proves that ΔH is negative in an exothermic reaction.
Image Courtesy of SilaVula
In the graph for an endothermic reaction, you can see that the products have a higher potential energy, implying that energy has been put into the system. This further proves that ΔH is positive for an endothermic reaction.
Image Courtesy of SilaVula
Now that you've seen the graph and been introduced to a few terms, let's put the two together and do a practice problem.
Image Courtesy of Socratic
(a) What is the potential energy of the reactants?
Just look at the y-axis for the reactants: 40 kJ!
(b) What is the potential energy of the products?
Similar to part a, just look at the y-axis for the products: 20 kJ.
(c) What is the value of ΔH?
ΔH is the difference between the potential energy of the products and the potential energy of the reactants.
Simply do: (PEproducts) - (PEreactants)
(20 kJ) - (40 kJ) = -20 kJ
In other words, 20 kJ of energy is released during this reaction.
(d) What is the activation energy?
To find the activation energy, you should be looking for two numbers: the potential energy of the reactants and the energy of the activated complex (the maximum point).
(energy of activation complex) - (PEreactants)
(100 kJ) - (40 kJ) = 60 kJ
In other words, it takes 60 kJ of energy to complete the reaction.
(e) Is this an endothermic or exothermic reaction?
Since ΔH is negative and the potential energy of the products is lower than that of the reactants, this is an exothermic reaction.
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