Question

Section: PRELIMINARY QUESTIONS (To be answered BEFORE coming to tav. 1. State the qualitative relationship between the amount of gas in your car tire and the pressure in that tire. When a spark plug fires in your car's engine two things happen as the gas burns--the gas gets hotter and more molecules of gas are produced. For ex- ample,... 2 CgH18 + 25 02 16 CO2 + 18 H20 a) which way does the piston move and how does the volume in the cylinder change in response to these combined effects? b) How would the piston move (and the volume change) in response to only the change in moles? c) How would the piston move (and the volume change) in response to only the change in temperature? 3. Using the data in the Discussion, calculate the weighted average of the mass of a mole of "air molecules". (Assume 24°C room temperature, 70% relative humidity, and one atmosphere pressure.) Given: You will use air (a mixture of gases) instead of one specific gas to study the quan- titative relationships between several physical properties of gases. Therefore, when you need the mass of a mole of "air molecules" to analyze the data, you will need to use a weighted average of the masses of the gases which make up air. Dry air is composed of N, (78.1% of the particles), 0, (21.0%), and Ar (0.9%) and trace amounts of other gases. At 1 atmosphere pressure (760 torr) this corresponds to pressures of 593.56 torr due to N2, 159.60 torr due to 02, and 6.84 torr due to Ar. (Note that extra digits in these calculations and those that follow have been retained beyond the allowed number of significant figures so that it is obvious that everything adds up correctly.) However, when there is 100% relative humidity, the percentages (and pressures) of all of these gases decrease accordingly. For exam- ple, around room temperature (at 24°C or approximately 75°F) the contribution to the pressure of the atmosphere from water vapor is 22.38 torr when the relative humidity is 100%. Therefore, if the total pressure is still 760 torr, then the remaining 737.62 torr is due to the gases present in dry air. Then 78.1% (576.08 torr) of the 737.62 torr would be Ng, 21.0% (154.90 torr) of it would be 02, and 0.9% (6.64 torr) of it would be Ar. At other temperatures, atmospheric pressures, or relative humid- ities the pressures of these gases would be different.

Answer 1

1) By increasing the amount of gas in the same space, the pressure of the gas molecules between them and the walls increases.

2) a) The piston moves up, since the volume of the gas expands.

b) Due to the change of moles, the piston moves upwards, the gas expands.

c) Due to the increase in temperature, the piston moves upwards, the gas expands.

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