Hot air rises, which is why hot-air balloons ascend through the atmosphere and why warm air collects near the ceiling and cooler air collects at ground level. Because of this behavior, heating registers are placed on or near the floor, and vents for air-conditioning are placed on or near the ceiling. The fundamental reason for this behavior is that gases expand when they are heated. Because the same amount of substance now occupies a greater volume, hot air is less dense than cold air.
The substance with the lower density—in this case hot air—rises through the substance with the higher density, the cooler air. A sample of gas cannot really have a volume of zero because any sample of matter must have some volume. The temperature scale is given in both degrees Celsius and kelvins.
The significance of the invariant T intercept in plots of V versus T was recognized in by the British physicist William Thomson — , later named Lord Kelvin. We can demonstrate the relationship between the volume and the amount of a gas by filling a balloon; as we add more gas, the balloon gets larger. Equal volumes of four different gases at the same temperature and pressure contain the same number of gaseous particles.
Because the molar mass of each gas is different, the mass of each gas sample is different even though all contain 1 mol of gas. Stated mathematically,. This relationship is valid for most gases at relatively low pressures, but deviations from strict linearity are observed at elevated pressures.
As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Skip to Content Go to accessibility page. Chemistry 2e 9. My highlights. Table of contents. Answer Key. By the end of this section, you will be able to: Define the property of pressure Define and convert among the units of pressure measurements Describe the operation of common tools for measuring gas pressure Calculate pressure from manometer data.
Figure 9. Convert a pressure of Hg into: a torr b atm c kPa d mbar Solution This is a unit conversion problem. The relationships between the various pressure units are given in Table 9. What is this pressure in atmospheres, in millimeters of mercury, in kilopascals, and in bar? Using very dense liquid mercury left permits the construction of reasonably sized barometers, whereas using water right would require a barometer more than 30 feet tall. Calculation of Barometric Pressure Show the calculation supporting the claim that atmospheric pressure near sea level corresponds to the pressure exerted by a column of mercury that is about mm high.
Plugging these values into the equation and doing the necessary unit conversions will give us the value we seek. The difference in height between the liquid levels h is a measure of the pressure.
Mercury is usually used because of its large density. Calculation of Pressure Using a Closed-End Manometer The pressure of a sample of gas is measured with a closed-end manometer, as shown to the right. The liquid in the manometer is mercury. Determine the pressure of the gas in: a torr b Pa c bar Solution The pressure of the gas is equal to a column of mercury of height The pressure at the bottom horizontal line is equal on both sides of the tube.
The pressure on the left is due to the gas and the pressure on the right is due to Calculation of Pressure Using an Open-End Manometer The pressure of a sample of gas is measured at sea level with an open-end Hg mercury manometer, as shown to the right. Determine the pressure of the gas in: a mm Hg b atm c kPa Solution The pressure of the gas equals the hydrostatic pressure due to a column of mercury of height Determine the pressure of the gas in: a mm Hg b atm c kPa a mm Hg; b 0.
If you exert less pressure, you are less likely to break through thin ice. Identify: With a closed-end manometer, no change would be observed, since the vaporized liquid would contribute equal, opposing pressures in both arms of the manometer tube.
Skip to main content. Chapter 9: Gases. Search for:. A smaller scale demonstration of this phenomenon is briefly explained in the following video:. Hg into: torr atm kPa mbar Show Answer This is a unit conversion problem. Show Answer 0. Example 2: Calculation of Barometric Pressure Show the calculation supporting the claim that atmospheric pressure near sea level corresponds to the pressure exerted by a column of mercury that is about mm high.
Show Answer Example 3: Calculation of Pressure Using a Closed-End Manometer The pressure of a sample of gas is measured with a closed-end manometer, as shown below. Show Answer The pressure of the gas is equal to a column of mercury of height Example 4: Calculation of Pressure Using an Open-End Manometer The pressure of a sample of gas is measured at sea level with an open-end Hg mercury manometer, as shown below. Show Answer The pressure of the gas equals the hydrostatic pressure due to a column of mercury of height Show Answer mm Hg 0.
Exercises The pressure of a sample of gas is measured at sea level with a closed-end manometer. Determine the pressure of the gas in: torr Pa bar The pressure of a sample of gas is measured with an open-end manometer, partially shown to the right. Assuming atmospheric pressure is Hg, determine the pressure of the gas in: torr Pa bar The pressure of a sample of gas is measured at sea level with an open-end mercury manometer. Assuming atmospheric pressure is mm Hg, determine the pressure of the gas in: mm Hg atm kPa Show Selected Answer 1.
The pressure of the gas is: [latex] Key Concepts and Summary Gases exert pressure, which is force per unit area. Exercises Why are sharp knives more effective than dull knives Hint: think about the definition of pressure? Why do some small bridges have weight limits that depend on how many wheels or axles the crossing vehicle has?
Why should you roll or belly-crawl rather than walk across a thinly-frozen pond? A typical barometric pressure in Redding, California, is about mm Hg. Calculate this pressure in atm and kPa. A typical barometric pressure in Denver, Colorado, is mm Hg. What is this pressure in atmospheres and kilopascals?
What is this pressure in atmospheres, in millimeters of mercury, and in kilopascals? Canadian tire pressure gauges are marked in units of kilopascals. What reading on such a gauge corresponds to 32 psi? During the Viking landings on Mars, the atmospheric pressure was determined to be on the average about 6. What is that pressure in torr and kPa? The pressure of the atmosphere on the surface of the planet Venus is about Compare that pressure in psi to the normal pressure on earth at sea level in psi.
A medical laboratory catalog describes the pressure in a cylinder of a gas as What is the pressure of this gas in atmospheres and torr? Consider this scenario and answer the following questions: On a mid-August day in the northeastern United States, the following information appeared in the local newspaper: atmospheric pressure at sea level What was the pressure in kPa? The pressure near the seacoast in the northeastern United States is usually reported near During a hurricane, the pressure may fall to near Calculate the drop in pressure in torr.
Why is it necessary to use a nonvolatile liquid in a barometer or manometer? How would the use of a volatile liquid affect the measurement of a gas using open-ended manometers vs.
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