I need the original questions from the Tianjin University version of the Chemistry Examination preparation materials – please help!
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Example: A container with a volume of V=30 L contains a certain gas whose density is 1.3 g/L. The container is connected to the atmosphere, and after some of the gas is removed, the pressure drops by 0.78 atm. What is the mass of gas that was removed, assuming the temperature remains constant? The correct answer given in the textbook is 17 g; I’m not quite sure about the method used to arrive at this answer, and it doesn’t match what I get. Please, experts, help me understand this! ! Thank you
What are the steps to solving this problem in the answer? Isn’t it necessary to use the ideal gas law here? This answer is really strange
The answer I calculated is also 17g; please check your calculations again, original poster!
Solution process: P1V = m1RT/M, P2 = P0, P2V = m2RT/M. Therefore, P1 = P0 + 0.78 = 1.78 atm. △m = m1 – m2; △m = m1 * 0.78/1.78 = 30 * 1.3 * 0.78/1.78 = 17 g. Question: Is m1 – m2 equal to m1*0.78/1.78?
P0V0 = n0RT, P1V1 = P1V0 = n1RT. Therefore, P0V0/n0 = P1V0/n1 = RT. Hence, n1 = P1/P0 * n0. m1 = P1/P0 * m0 = 1/1.78 * 30 * 1.3 = 21.9 g (the remaining amount). m2 = (P0 – P1)/P0 * m0 = 0.78/1.78 * 1.3 * 30 = 17.09 g (the amount released). The answers in the book are correct. (Haha, I made a mistake just now. ) This post was last edited by lucky1909 on 2009-3-26 at 14:48 ]
Please check the question carefully, OP. I think the conditions given aren’t very clear – whether it’s not connected to the atmosphere or whether it becomes connected to the atmosphere after exhaust is released. In this case, it should be connected to the atmosphere after exhaust is released, so 17 grams is the correct answer. It’s likely that the question wasn’t clear enough, leading to some misunderstandings.
How come the original poster still doesn’t understand the process?:lol It’s already very clear above; in simple terms, the process is as follows: the initial pressure is 1.78, and after some of the pressure is released, it becomes 1 atmosphere, which means 0.78 units of pressure have been released. According to the ideal gas law, this amount is proportional to the pressure. So, 39 is simply multiplied by 0.78/1.78 to get the result.
Haha, water got into the brain and caused a short circuit! Got it, thanks!
It’s easy to misread this question; one might think that the initial pressure is 1 atm and that 0.78 atm has been removed
I have the basic exam today; I hope to pass it on the first try.
It would be great if there were questions like this; so easy!