# HW 5 - approximately 390 ppm how long will it take before...

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53:050 Natural Environmental Systems Homework Assignment No. 5 – Spring 2011 → Due Friday February 18 at 8:30 am ← 1. Problem 2-15 in Davis and Masten. Also , calculate the half-life of the chemical and report your answer in days. 2. (a) Problem 2-16 in Davis and Masten. (b) The reaeration rate coefficient (k a ) is a function of temperature. This relationship can be described using the following equation: k a (T) = 0.038(1.024) T-20 . Rework Problem 2-16 assuming the stream temperature is 28 o C. Under these conditions, how long (in days) will it take for the dissolved oxygen to increase from 2.5 to 6.5 mg/L? (c) Compare your answers to (a) and (b). Explain why there is a difference between to two values, if there is any. The difference in temperature is not a sufficient enough answer. 3. Carbon dioxide (CO 2 ) is considered to be a major greenhouse gas. It has been estimated that the half- life of CO 2 in the atmosphere is about 50 years. If the current CO 2 concentration in the atmosphere is

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Unformatted text preview: approximately 390 ppm, how long will it take before the CO 2 concentration decreases to a level of 290 ppm, the approximate level prior to the industrial revolution, assuming no additional CO 2 emissions. 4. The following are data taken from an experiment assessing the removal of an organic chemical from water using oxidation by ozone. Do these data fit a 0-order, 1 st-order, or 2 nd-order rate expression? Provide sufficient justification for your answer, and report the correct rate coefficient in the correct units. Time (hr) Concentration of organic (mg/L) 15 6 8.1 12 5.3 24 3.3 48 1.9 72 1.2 96 1.0 5. Dr. Whacko needs to know the rate at which his new bird flu vaccine decomposes in water. He conducts a batch experiment that gives the following data. (a) Is this a 0-order, 1 st-order, or 2 nd-order reaction? WHY? (b) What is the rate coefficient, reported in the correct units ?...
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