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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
⏱️ 4 min read
August 23, 2020
Phase changes could be represented in a variety of ways! The following curves might help you understand the relation between phase changes and endothermic/exothermic processes more.
We can more importantly see how transitions between states of matter work energetically through a heating curve:
Image Courtesy of Schoenherr & Diamantopoulos Chemistry Videos
Here, the x-axis is the progress of the reaction, or span of time, and the y-axis is temperature🌡️. We see the transition from solid to liquid to gas as temperature increases. This shows how as you introduce energy into a system, the system goes from a solid to a liquid to a gas.
It makes sense that temperature increases as you go from solid to liquid to gas, but what are those plateaus marked melting and vaporizing? Well, for a short time while transitioning states, you need to use energy to actually melt or boil the object.
To restate this, you not only need to get up to the proper temperature, but you also must add energy to melt/boil all of it. These are called the heats of fusion (Hf) and heats of vaporization (Hv) going from left to right.
So think about it: a solid melts into a liquid, right? But there is a transition between the two states. The solid stays at 0°C until it is completely melted into a liquid, and then the heating curve progresses.
The heat of vaporization is almost always higher than the heat of fusion. This makes it takes more energy for something to boil than it takes for it to melt. This is why the vaporizing plateau is longer...it takes more time for the water to fully boil.
Think about this in terms of IMFS. During the melting phase, only some IMFS break. However when water melts, all of them have to break, which requires more energy⚡.
How many Joules are required to change 30.0g of ice at -20°C to steam at 140°C? There are a few steps you should follow using the following given information:
The specific heat of ice is 2.108 J/g*°C 🧊
The specific heat of water is 4.18 J/g*°C 💧
The specific heat of steam is 2.010 J/g*°C 😤
Hf for H2O = 334 J/g
Hv for H2O = 2260 J/g
There are actually 5 different (quick) calculations you must perform to calculate the answer:
🧊Solid - q=mcΔT - (30.0g)(2.108)(20°C) = 1264.8 J
ΔT was obtained by (-20°C - 0°C). O°C is the melting point of water.
Melting - Hf(m) - (334 J/g)(30.0g) = 10020 J
💧Liquid - q=mcΔT - (30.0g)(4.18)(100°C) = 12540 J
ΔT is obtained by subtracting the melting point of 0°C from the boiling point of 100°C
Vaporizing - Hv(m) - (2260 J/g)(30.0g) = 67800 J
😤Gas - q=mcΔT - (30.0)(2.010)(40°C) = 2412 J
ΔT is obtained by subtracting the boiling point of 100°C by the final temperature of 140°C
Add them all together to get a final answer of 94,036.8 J or 94.0 kJ
Cooling curves show the exothermic processes, which is the opposite of the endothermic processes the heating curve shows.
Image Courtesy of Schoenherr & Diamantopoulos Chemistry Videos
The cooling curve is the exact same as the heating curve, but it has the heats of condensation and heats of freezing instead. The heats of condensation and freezing are simply the NEGATIVES of the heats of fusion and vaporization.
As we know, there are three phases of matter: solid, liquid, and gas. Many of you also may know that you can transition between the three phases through melting, boiling, condensing, or freezing. This can be seen graphically in a phase diagram:
Image Courtesy of Aakash Shah
On the two axes, we have pressure in atmospheres and temperature in Celsius. This shows the relationship between pressure and temperature in determining which state of matter an object is in. As we increase temperature (at a sufficient pressure), we move from solid to liquid to gas, and vice versa.
There are two important points on the phase diagram, the triple point and the critical point. The triple point is a weird point where you are in all three states of matter. The critical point is a point at which past this point you can no longer have a liquid, you either have a supercritical fluid or a gas. Here's an animation showing you the triple point of water:
Image Courtesy of UCSC Physics
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