Chem Lab #8 Report

Chem Lab #8 Report - Lab #8 Report: Energy of Phase Changes...

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Lab #8 Report: Energy of Phase Changes Sarah Aistrup Sirus Saeedipour Michael Aldrighetti Hasan Naser Sec. 425 Cassie Ward
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INTRODUCTION: The purpose of this lab was to determine the energy involved in phase changes of: 1. Ice (H 2 O (s) ) 2. Liquid nitrogen (N 2 (l) ) 3. Dry ice (CO 2 (s) ) A phase change can be referred to as the “transformations from one phase to another” (Chang 489). This investigation will be contemplating the energy of phase changes of ice, liquid nitrogen, and dry ice when placing them into contract with water in a well insulated Styrofoam cup. By doing so, the “heat energy is transferred from the first (warmer) substance to the second (cooler) substance with minimal energy loss to the surrounding system (Chem Lab). Calorimetry will once again be employed from the previous lab on thermochemistry because it allows for the measurement of heat involved in these phase changes. These measurements will be collected by the LoggerPro software. Calculating the energy change may be done according to the equation: q = msDT J = g * [J/(g * ºC] * ºC Where m is the mass, temperature change is DT and s is specific heat for water. s = 4.181 J/g ºC There are three states of matter: gas, liquid and solid. Each state of matter has their own characteristic properties. Solids have the most ordered molecular structure, their molecules vibrate about a fixed position. This is followed by liquids, then gasses, who's molecules have very free motion (Change 462). When a substance is undergoing a phase change, energy in the form of heat must be supplied or removed from the substance. As this physical change is occurring, the molecular order characteristic of a state of matter is either increasing or decreasing. Examined here will be fusion, vaporization, and sublimation. In the diagram below it is easy to see how they are related. Fusion is the transformation of a liquid to a solid or vise-versa. This physical change takes place when a substance is melted or frozen. When the solid, such as ice is heated, it gains energy until reaching it's melting point, meaning solid and liquid phases are in sync. As more energy is added, the ice changes phase. However, “during this phase change, the temperature stays the same, resulting in a liquid at the melting point temperature” (Chem Lab). “The 'normal' melting (or freezing) point of a substance is the temperature at which the substance melts (or freezes) at 1 atm pressure” (Chang 495). Vaporization involves the phase change between liquids and gasses. When a liquid is heated the boiling point is reached. The heat energy causes the liquid molecules to have a greater kinetic energy causing them to change phase into a gas. Once again, the temperature stays the same at a substances' boiling point. Condensation describes the gas changing to a liquid.
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This note was uploaded on 04/14/2010 for the course CHEM 13891 taught by Professor Hierl during the Spring '10 term at Kansas.

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Chem Lab #8 Report - Lab #8 Report: Energy of Phase Changes...

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