Lab05EJM - Name_Erica Murray_ Lab #5 :EVAPORATION RATES, %...

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Name____Erica Murray_______ Lab #5 :EVAPORATION RATES, % MOISTURE & THICKNESS OF Al FOIL NOTE to Instructor: Unable to complete this lab do to scale. I completed it to my best ability. by Dr. Adams (5-03 edit.) In this laboratory exercise you will be measuring the evaporation rates of tap water and one other liquid. At room temperature, water and other volatile liquids evaporate. At a fixed (set) temperature molecules of a liquid have an average kinetic energy . Temperature is a direct measurement of kinetic energy. At the same temperature some molecules have a larger kinetic energy than others. At the surface of the liquid some molecules possess sufficient kinetic energy to break the chemical bonds around them and escape the liquid and inter into the gas (vapor) state. If the temperature of the liquid is increased, a larger % of the particles at the surface of the liquid have sufficient energy to escape. Thus at higher temperatures, the evaporation rate increases. In a closed container each gas particle exerts a pressure against the container wall when it strikes the container. As the temperature of the system increases, the velocity of gas particles also increases. At higher temperatures the gas particles are traveling at a higher velocity and there are also more gas particles that have evaporated. Both of these contributions result in a higher gas pressure in a closed system at higher temperatures. In the cooling system of automobile engines, as the temperature of the circulating cooling water increases, the vapor pressure inside the circulation system increases. If the water becomes too hot, too much vapor pressure builds up resulting in the failure or breakage of the connecting hoses. The internal bonds that hold molecules together are related to the evaporation rate. The stronger the internal bonds that hold the molecules together, the more energy it takes to break these bonds. If the molecule-to-molecule bonds are stronger, then it will take a comparatively higher temperature to break those bonds. Thus evaporation rates are slower when molecule-to- molecule bonds are stronger. Weaker bonds result in a faster evaporation rate. Water is often a reference point for evaporation. If a liquid is placed on your skin and it feels cooler than water would feel, then most likely that liquid is evaporating faster than water. Evaporation is an endothermic event. An endothermic reaction is one in which energy is a reactant in an equation. For example: Water (liquid) + heat water (gas) The water vapor molecules have pulled heat away from the liquid when evaporating. Thus there is less kinetic energy left behind in the liquid. This results in an average lower temperature of the liquid water left behind. This endothermic event is the basis of your sweat cooling your body. As the water evaporates, it carries away heat from your body at the skin level. Thus you are cooled by the evaporation event. The faster the evaporation rate, the greater the cooling effect on the local environment.

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This note was uploaded on 05/06/2010 for the course CHEM 101 taught by Professor Griffith during the Spring '08 term at Illinois Valley CC.

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Lab05EJM - Name_Erica Murray_ Lab #5 :EVAPORATION RATES, %...

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