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# q9asol - g 1 before the system has solidified So T g 2< T...

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3.091 Fall Term 2004 Homework Quiz #9A solution outline (a) A melt of silicate glass, g 1 , cooled at rate, r 1 , has glass transition temperature, T g 1 . A new glass, g 2 , is formulated by the addition of CaO to g 1 . If a melt of g 2 is cooled at rate, r 1 , how does the glass transition temperature, T g 2 , compare to T g 1 ? Explain with reference to atomic structure. If g 2 is cooled at rate, r 1 , the glass transition temperature, T g 2 , will lie below T g 1 . The addition of CaO to g 1 promotes chain scission of the silicate network. The resulting decrease in viscosity of the g 2 melt allows for greater mobility than would be the case in the g 1 melt at comparable undercooling. Accordingly, if each melt is cooled at the identical rate, it is necessary to cool g 2 to a lower temperature than
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Unformatted text preview: g 1 before the system has solidified. So T g 2 < T g 1 . (b) The fictitious compound, arrhenium fluoride (AhF), decomposes readily at temperatures exceeding 37ºC. The figure below shows how the rate of reaction varies with the concentration of AhF. The rate, r , is in units of M s –1 and the concentration of AhF, c , is in units of M (mole L –1 ). The slope has a value of 1.67 and the intercept has a value of 0.490. log (rate) log (concentration) (i) What is the order of reaction? n = 1.67 (ii) Calculate the value of the rate constant. The value of the rate constant is given by the intercept of the plot of log rate versus log concentration. Therefore, ⎛ mol ⎞ − 0.67 k = 10 0.490 = 3.09 ⎜ ⎝ L ⎠ ⎟ 1 s...
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