Principles 1 Week 16

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Monday December 4, 2023 Day 68 Phase Diagrams
Textbook Readings 11.8: Phase Diagrams	Course Lectures 11.4 pdf Video Phase Diagrams
11.4 Phase Diagrams	Phase Changes, Heats of Fusion and Vaporization, and Phase Diagrams
Homework Problems Refer to the phase diagram at right when answering questions 76.1 - 76.6 76.1 What are the physcal states corresponding to regions i. , ii. , iii. and iv. 76.2 What is carbon dioxide's physical state at room temperature (~23^oC) and atmospheric pressure (1 atm)?
76.3 What it the meaning of the "triple point" and what is the temperature and pressure corresponding to CO₂'s triple point? 76.4 What is the physcial state of CO₂ at a pressure of 80 atm and a temperature of 40^oC? 76.5 A CO₂ sample at a pressure of 60 atm and a temperature of -20^oC is warmed to a temperature of 40^oC while keeping the pressure constant. What is the order of phase changes that occur along this path? 76.6 Consider a CO₂ sample at 140 atm and -58^oC. If the pressure is gradually decreased to 0.1 atm, what phase changes are observed? 76.7 What is a supercritical fluid? 76.8 Examine water's phase diagram available here. What phase changes occur as you go from point A to point B. What is so unusual about the order of these phase changes? Click and drag the region below for correct answers 76.1 i. Solid ii. Liquid iii. Gas iv. Supercritical fluid 76.2 Click here: Gas 76.3 Click here: The triple point is that set of conditions that CO₂ can exist simultaneously as a solid, liquid and gas. For CO₂, this corresponds to T = -56.57 ^oC and P = 5.11 atm. 76.4 Click here: Supercritical Fluid 76.5 Click here: Liquid -> gas 76.6. Click here: Decreasing the pressure eventually leads to the solid converting into a liquid. Finally, the liquid changes into a gas. . 76.7. A supercritical fluid exists at pressures and temperatures where liquid and gas phases become indistinguishable. View this video link for more information on supercritical fluids. 76.8 As pressure is increased, the density of the material must increase. This water system begins as a gas. As pressure is increased, the gas is converted into a solid. As even more pressure is applied, the solid is converted into a liquid. In other words, solid water (a.k.a. ice) is more dense than water vapor. However, ice is less dense than liquid water. For most materials, the solid phase is the most dense. However, in the case of water, the liquid phase is the most dense!

Tuesday December 5, 2023 Day 69 WATER! A Unique Substance!
Textbook Readings 11.9: Water - An Extraordinary Substance	Course Lectures 11.9 pdf Video Water; a unique substance
Objectives 1. Identify water's unique characteristics and give examples of each.	Water - Liquid Awesome: Crash Course Biology #2

Homework Problems 77.1 What's so special about water? 77.2 Water is a very polar solvent and therefore best dissolves polar solutes. Which of the following would not dissolve well in water? a. CO₂ b. O₂ c. K₂SO₄ d. CH₃OH e. KCl f. HNO₃ g. AgCl 77.3 The density of solid water (a.k.a. ice) is less than that of liquid water. Why is this and why is it important in nature? 77.4 Local large bodies of water help control the temperatures of areas around them. How is this possible? 77.5 Why do you feel cooler when sweat evaporates? 77.6 When diluting strong acids with water, the process is exothermic and generates a lot of heat. Consequently, the rule is to ALWAYS add the acid to water and NOT add water to strong acid. Why is this? (Specific heats: c_H2O = 4.184 J/g^oC c _H2SO4 = 1.34 J/g^oC Click and drag the region below for correct answers 77.1 Water molecules form strong hydrogen bonds Liquid water is very cohesive. Water is the only substance known to exist in all 3 forms (solid, liquid and gas) naturally on the surface of the earth. Water is a polar solvent and dissolves ionic substances easily. It is an "Amazing Solvent!" Water has a very high specific heat. 77.2 CO₂ & O₂ are non-polar molecules and don't dissolve well in water. AgCl is insoluble (think solubility rules) and doesn't dissolve well in water. 77.3 Unlike most substances, the density of solid water (a.k.a. ice) is LESS than the density of liquid water. Consequently ice floats. We observe this when as ice cubes floating in a drink. Also, forms and floats on the top of a lake while the majority of the lake is now insulated and stays liquid (Fish are very thankful!). The spacing between molecules for ice is GREATER than the spacing between molecules for liquid water. Because ice contains more empty space, it is less dense. 77.4 Water has a high heat capacity. This means it can absorb a lot of heat energy without significantly changing its temperature. With so much heat stored in the neighboring water, less is available to heat the surroundings. 77.5 As water evaporates (an endothermic process), hydrogen bonds are broken and this energy is removed. Removing energy lowers the temperature of the skin. This is especially significant because of water's high ΔH_vap 77.6 Diluting acids produces a lot of heat and so to avoid possible (& dangerous) boil-overs, we want to minimize the temperature change that takes place. Water has an especially high specific heat in comparison to other liquids and this means it can absorb a lot of heat and only experience a modest change in temperature. So, adding acid to water let's the water absorb most of the heat and keeps the temperature under control.

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