7. Gases

Pressure Units

**Pressure** is the force that is exerted within a given volume of space.

Understanding Pressure

1

concept

## Pressure Units

1m

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the S. I. Unit for pressure is the pascal, abbreviated as P. A. And it's named over the french mathematician Blaise pascal when it comes to pressure. Let's think about what that really means. When it comes to gasses, they can be seen as a collection of molecules that move in random directions in straight lines. So here we have an image of a container inside of these containers. We have these blue dots which represent gas molecules. All they're doing is bouncing around randomly bumping into the sides of the container, bumping into each other. How does this apply to pressure? Well, pressure is the force that a gas exerts on the wall of its container connected to pressure. Are two ideas F which equals force in S. I. Units of newtons and A. Which represents area and it's S. I. Unit is in meters squared. So pressure itself is just the force that the gasses exert over an area. So here we're gonna say that pressure equals force over area. This idea of gasses existing within containers are gonna be delved deeper into. When we talk about ideal gasses and eventually non ideal gasses

**Pressure **represents the force that a gas molecule exerts against the walls of its container. It can be depicted as force per area.

2

example

## Pressure Units Example 1

48s

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in this example question. It says what happens to the pressure if the same amount of gas molecules is transferred from a five liter container toe a 10 liter container? Remember, pressure equals pressure equals force over area. They're saying it's the same amount of gas molecules. Since it's the same amount of gas molecules, they should exert the same type of force. But what's happening? We're going from a five liter container toe, a 10 liter container, so our area is going up the size inside the container is increasing, so if force is staying the same but areas increasing, that's gonna cause my pressure to decrease. So here, our best option would have to be Option B, where it's going to decrease.

3

concept

## Pressure Units

1m

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additional non S i units for pressure used by chemists are atmospheres, which is ATM millimeters of mercury, which is MM H G. And then just tour. Now these units for pressure have their own pressure value, which can be related to one another. Now, remember, if you see a purple box that people box means you have to memorize it because usually it's not given to you in terms of a quiz or exam. Now the pressure values associated with atmospheres Millimeters of Mercury and Tour are one 7 60 and then 60 again. Now the less commonly known ones. Pascal's cable, Pascal's bars and slides are in purple boxes, meaning they're not usually expected to be memorized. They'll be given to you in some way within the question or formula sheet. Now they're pressure. Values are 1.13 to 5 times 10 to the five kilo. Remember, Kilo was 10 to the three, so this is one on 1.3 to 5 bars. Here is 1.13 to 5. And then finally, if we look at Sai Sai is 14.696 now, these numbers relate to one another. We said that there a way to relate to each each other to each other. That means that one atmosphere equals 7 millimeters of mercury, or 1.13 to 5 bars equals 7, 14, 696 size. So these are just ways of them connecting toe one another. But again, it's the first three that are gonna be the most important. Even though they're non s I units, they're the ones most commonly used by chemist. So now that we know these different types of pressure values, let's continue onward to an example quest.

4

example

## Pressure Units Example 2

2m

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in this example question. It says the pressure in Denver, Colorado, which has an elevation of 5280 ft, averages about 24.9 inches. Mercury. Now we have to convert this pressure into millimeters of mercury and atmospheres. All right, so this is basically a dimensional analysis type of question. We have to convert from inches Mercury two millimeters of mercury. Once we have that, we can then change those millimeters of mercury into atmospheres. So let's start out with 24 inches. Mercury. We want to get rid of inches mercury. So we're gonna put inches mercury on the bottom. And then remember that from the mental analysis, we know there's a relationship between inches and centimeters, so we're gonna go from inches Mercury two centimeters. Mercury now recall. If you've looked at my dimensional analysis videos, you know that one inch is equal to 2. centimeters. Here are inches Mercury cancel out, and now we have centimeters of mercury. Now we want to get rid of centimeters of mercury, So put it on the bottom and we can go from Centimeters two millimeters and we could stay here that 1 70 m is 10 millimeters. Casting out everything that will have left at the end is millimeters of mercury, which comes out to 6. 32.46 millimeters of mercury. Now, because our values within the question have 366 with 24.9, not 24.9 and 366 here is Well, we're gonna put this in 366 So 6. 32 millimeters of mercury. Now we want atmospheres. So let's take that 6. 32.46 millimeters of mercury. And we're gonna convert that into atmospheres. So remember, here one atmosphere is equal to 760 millimeters of mercury. So when we do that, we're gonna get as our answer 0.832 atmospheres as our final answer. So just approach this like any dementia analysis type of question. Thio convert from one pressure unit, toe another

Additional resources for Pressure Units

PRACTICE PROBLEMS AND ACTIVITIES (48)

- The recommended pressure for inflation of an automobile tire is 35 psi. What is the pressure in units of mm H...
- What is the pressure of the gas inside the bulb (atm) if the outside pressure is 0.92 atm? (a) 1.1 atm (b) 2...
- (b) Explain why the stratosphere, which is about 35 km thick, has a smaller total mass than the troposphere, w...
- (a) How are the boundaries between the regions of the atmosphere determined?
- (b) Which units are appropriate for expressing atmospheric pressures, N, Pa, atm, kg>m2?
- A person weighing 75 kg is standing on a threelegged stool. The stool momentarily tilts so that the entire wei...
- A person weighing 75 kg is standing on a threelegged stool. The stool momentarily tilts so that the entire wei...
- (b) What pressure, in atmospheres, is exerted on the body of a diver if she is 10 m below the surface of the w...
- (a) How high in meters must a column of ethanol be to exert a pressure equal to that of a 100-mm column of mer...
- (a) The compound 1-iodododecane is a nonvolatile liquid with a density of 1.20 g>mL. The density of mercury...
- The highest barometric pressure ever recorded was 823.7 torr at Agata in Siberia, Russia on December 31, 1968....
- The highest barometric pressure ever recorded was 823.7 torr at Agata in Siberia, Russia on December 31, 1968....
- The highest barometric pressure ever recorded was 823.7 torr at Agata in Siberia, Russia on December 31, 1968....
- Perform the following conversions: (d) 1.323 * 105 Pa to atmospheres
- Perform the following conversions: (b) 0.685 bar to kilopascals
- Hurricane Wilma of 2005 is the most intense hurricane on record in the Atlantic basin, with a low-pressure re...
- Hurricane Wilma of 2005 is the most intense hurricane on record in the Atlantic basin, with a low-pressure re...
- Hurricane Wilma of 2005 is the most intense hurricane on record in the Atlantic basin, with a low-pressure rea...
- A glass tube has one end in a dish of mercury and the other end closed by a stopcock. The distance from the su...
- If the atmospheric pressure is 0.995 atm, what is the pressure of the enclosed gas in each of the three cases ...
- If the atmospheric pressure is 0.995 atm, what is the pressure of the enclosed gas in each of the three cases ...
- An open-end manometer containing mercury is connected to a container of gas, as depicted in Sample Exercise 10...
- The pressure in Denver, Colorado (elevation 5280 ft), averages about 24.9 in Hg. Convert this pressure to eac...
- The pressure in Denver, Colorado (elevation 5280 ft), averages about 24.9 in Hg. Convert this pressure to each...
- The pressure in Denver, Colorado (elevation 5280 ft), averages about 24.9 in Hg. Convert this pressure to each...
- The pressure in Denver, Colorado (elevation 5280 ft), averages about 24.9 in Hg. Convert this pressure to each...
- The pressure on top of Mount Everest (29,029 ft) averages about 235 mmHg. Convert this pressure to each indica...
- The North American record for highest recorded barometric pressure is 31.85 in Hg, set in 1989 in Northway, Al...
- The world record for lowest pressure (at sea level) was 652.5 mmHg recorded inside Typhoon Tip on October 12,...
- The world record for lowest pressure (at sea level) was 652.5 mmHg recorded inside Typhoon Tip on October 12,...
- (d) If you measure pressure in bars instead of atmospheres, calculate the corresponding value of R in L-bar/...
- Given a barometric pressure of 751.5 mmHg, calculate the pressure of each gas sample as indicated by the manom...
- Given a barometric pressure of 751.5 mmHg, calculate the pressure of each gas sample as indicated by the manom...
- Yet another common measure of pressure is the unit pounds per square inch (psi). How many pounds per square i...
- If the density of water is 1.00 g/mL and the density of mercury is 13.6 g/mL, how high a column of water in me...
- Why do gases exert pressure?
- Atmospheric pressure at the top of Pikes Peak in Colorado is approximately 480 mm Hg. Convert this value to at...
- Carry out the following conversions: (a) 352 torr to kPa
- Carry out the following conversions: (b) 0.255 atm to mm Hg
- What is the pressure in millimeters of mercury inside a container of gas connected to a mercury-filled open-e...
- What is the pressure in atmospheres inside a container of gas connected to a mercury-filled open-end manomete...
- Assume that you have an open-end manometer filled with ethyl alcohol 1density = 0.7893 g>mL at 20 °C2 rathe...
- Torricelli, who invented the barometer, used mercury in its construction because mercury has a very high densi...
- An ordinary gasoline can measuring 30.0 cm by 20.0 cm by 15.0 cm is evacuated with a vacuum pump. Assuming tha...
- Name the regions of the atmosphere. What property is used to distinguish between different regions of the atm...
- The troposphere contains about three quarters of the mass of the entire atmosphere. The troposphere is only 1...
- Pakistan's K2 is the world's second-tallest mountain, with an altitude of 28,251 ft. Its base camp, where clim...
- Force per unit area is termed ________.