# HW_5_key - Problem 3.2 The formula of the molecule is C3H6...

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Problem 3.2 The formula of the molecule is C 3 H 6 Because the pressure is low (14.7 psia) the Ideal Gas Law can be used. Thus, calculate the molecular weight as follows. PV nRT m m PV RT M RT RT M V ρ = = = = 3 3 0.103 (100 460) 10.73 42.10 l / 14.7 lb psi ft R M RT b lb mol psi ft R lb mol + = = = - - o o The number of hydrogen atoms (2) for each carbon atom is given. Ttherefore, the general formula of the molecule will have the form C n H 2n . With this information, the molecular weight formula is set up: ( ) 2 ( ) 12 2 14 / 42.1 / 3 molecule M M C n M H n n n nlb lb mole lb lb mole n = + = + = - = - = Then, the formula of the molecule is C 3 H 6 (Propene) Problem 3.7 The porosity of the sandstone is 0.18 or 18% Use the following equation in order to calculate porosity: void bulk solid bulk bulk V V V Porosity V V - = = The Ideal Gas behavior is used to model the process taking place in the two cells. First, there is gas at certain conditions of P & T in cell 1 occupying a volume V1-Vs. Then, the valve is opened and the gas expands at constant T to a new volume V2-Vs where V2 is the sum of the volumes of the two vessels. Then by difference, the solid volume of the sandstone is calculated and with this information, the porosity is determined. First, write the equation of an Ideal Gas for the initial condition: 1 1 1 1 1 (5 ) P V nRT P Vs nRT = - = Second, write the Ideal Gas Law for the final condition after the valve is opened: 2 2 1 2 1 (10 ) P V nRT P Vs nRT = - = Here, Vs is the solid volume of the sandstone.

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Third, combine both equations as follows: 2 2 1 1 1 1 2 1 1 1 1 2 1 2 1 (10 ) (5 ) 10 5 10 334.7 5 760 1.0651 334.7 760 P V P V T T P Vs P Vs T T P P Vs P P Vs cc = - - = - = - - = = - Now, the porosity is determined: 1.3 1.0651 0.18067 18% 1.3 void bulk solid bulk bulk V V V Porosity V V - - = = = = Problem 3.11. The tank will collapse in 3.66 minutes. To solve this problem, a force balance should be applied over the tank’s roof to determine the pressure inside the tank at which the roof will collapse. Because a vacuum will be generated, the pressure inside the tank will decrease below the atmospheric pressure. As more fluid is withdrawn
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HW_5_key - Problem 3.2 The formula of the molecule is C3H6...

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