9.1 Gas Pressure

Any gas exerts a pressure on the earth's atmosphere.

We are sensitive to pressure changes, for example, when your ears "pop" during take-off and landing, or when you dive underwater.
Gas pressure is caused by the force of gas colliding with objects.
The force of each collision is small, but a large number ofcollisions in a short time can result in a high pressure.
Air pressure is strong enough to crush a metal container if it isn't balanced by equal pressure from inside.

The atmosphere above us exerts a large pressure on objects at the surface of the earth, roughly the weight of a bowling ball pressing on an area the size of a human thumbnail.

The video shows a railway tanker car imploding when its internal pressure is decreased.

The phenomenon is explained in a small scale demonstration.

The weight of the column of air in the atmosphere above an object causes atmospheric pressure.

The pressure at sea level is similar to that of a full-grown African elephant standing on a doormat, or a bowling ball resting on your thumbnail.
Life on earth has evolved under such atmospheric pressure, even though these seem like huge amounts.

The force and area are directly proportional to pressure.

Increasing the amount of force or decreasing the area over which it is applied can increase or decrease the pressure.

The elephant exerts less pressure than the skater and is less likely to fall through thin ice.

The figure skater exerts a much higher pressure on the ice due to the small surface area of her skates because of the large force on the ground.

The pressure is 29.2 in.

The problem is a unit conversion.

There are relationships between pressure units.

The barometric pressure in Kansas City is 740 torr.

A barometer is a glass tube that is closed at one end and filled with a nonvolatile liquid such as mercury, and then inverted and immersed in a container of that liquid.

The atmosphere exerts pressure on the liquid outside the tube, the column of liquid exerts pressure inside the tube, and the pressure at the liquid surface is the same inside and outside the tube.
The tube's height is proportional to the pressure in the atmosphere.

Using very dense liquid mercury permits the construction of reasonably sized barometers, whereas using water would require a barometer more than 30 feet tall.

If the liquid is water, normal atmospheric pressure will support a column of water over 10 meters high, which is inconvenient for making and reading a barometer.

The value we seek will be given by plugging these values into the equation.

The height of a column of water should correspond to normal atmospheric pressure.

The water density is 1.0 g/ cm3.

A closed-end manometer has a tube with one closed arm and a nonvolatile liquid in between.

One of the arms of an open-end manometer is open to the atmosphere.

The difference in pressure between the container and the atmosphere is related to the distance between the liquid levels.

A manometer can be used to measure the pressure of gas.

Mercury has a large density.

A closed-end manometer is used to measure the pressure of a sample of gas.

Mercury is in the manometer.

The pressure of the gas is equal to a column of mercury.

A closed-end manometer is used to measure the pressure of gas.

Mercury is in the manometer.

The gases are shown to the right.

The pressure of the gas is equal to the pressure of the atmosphere at sea level.

The open-end Hg manometer is used to measure the pressure of a sample of gas.

It consists of an inflatable cuff to restrict blood flow, a manometer to measure the pressure, and a method of determining when blood flow starts and stops.

It has been an essential medical device since its invention.
There are many types of sphygmomanometers, including manual ones that require a stethoscope and are used by medical professionals, mercury ones that are used when the most accuracy is required, and digital ones that can be used with little training.
When using a sphygmomanometer, the cuff is placed around the upper arm and inflated until blood flow is completely blocked.
Blood flowing through the arteries causes a rise in pressure when the heart beats.
When the cuff's pressure is equal to the blood pressure, it creates audible sounds that can be heard using a stethoscope.
As the heart's ventricles prepare for another beat, there is a decrease in pressure.
Blood pressure units from a sphygmomanometer are in grams of mercury.

Throughout the ages, people have observed clouds, winds, and precipitation, trying to discern patterns and make predictions: when it is best to plant and harvest; whether it is safe to set out on a sea voyage; and much more.

Our civilization and the environment will be impacted by weather and atmosphere related challenges.
Chemicals are used to help us understand weather, the atmosphere, and climate.
There are meteorology, climatology, and atmospheric science.
The study of the atmosphere, atmospheric phenomena, and atmospheric effects on the weather is called meteorology.
Predicting the weather in the short term can save lives and help the economy.
Weather forecasts are the result of thousands of measurements of air pressure, temperature, and the like, which are compiled, modeled, and analyzed in weather centers worldwide.

Weather maps are used to describe and predict weather.

Weather conditions can be affected by regions of high and low pressure.
The isobars are locations of constant pressure.

When the earth's surface atmospheric pressure is lower than the surrounding environment, moist air rises and condenses, producing clouds.

Most weather events are caused by the movement of air and water.

The atmosphere surrounds a planet.

The atmosphere on Earth is roughly 125 km thick and consists of 78.1% nitrogen and 21.0% oxygen.
Air density and temperature go down as you go higher.

The troposphere is one of the five layers of Earth's atmosphere.

The study of the climate, averaged weather conditions over long time periods using atmospheric data is called Climatology.

Climatologists study patterns and effects that occur over decades, centuries, and millennia, which is why the OpenStax book is free.
Atmospheric science combines meteorology, climatology, and other scientific disciplines to study the atmosphere.

A desire to understand nature and a quest to make balloons in which they could fly a number of scientists established the relationships between the physical properties of gases during the 17th and 18th century.

It's quite accurate for low pressures and moderate temperatures.
The ideal gas law will be put together after we consider the key developments in individual relationships.

The first hydrogen-filled balloon flight, manned hot air balloon flight, and manned hydrogen-filled balloon flight occurred in 1783.

The frightened villagers of Gonesse destroyed the balloon with pitchforks and knives.
400,000 people watched the launch of the latter in Paris.

Imagine filling a container with gas and then sealing it so that no gas escapes.

The gas inside gets colder if the container is cooled.

The volume and number of moles of gas are constant since the container is tightly sealed.

The pressure of the gas in the sphere is low when the hot plate is off.

The pressure of the gas in the sphere increases as the gas is heated.

Any sample of gas confined to a constant volume has a relationship between temperature and pressure.

An example of experimental pressure-temperature data is shown for a sample of air.

If the temperature is inkelvin, the pressure and temperature are proportional.

The lowest possible temperature is called absolute zero, which is 0 on the kelvin scale, when this line is adjusted to lower pressures.

The relationship between the pressure and the temperature of a gas was established by Guillaume Amontons and Joseph Louis Gay-Lussac.

There is a confined gas at constant volume.

Until it is empty, a can of hair spray is used.

High pressure could cause the can to burst.

A sample of nitrogen, N2, occupies 45.0 mL at 27 degC and 600 torr.

Let's say we fill a balloon with air and seal it, it will have a specific amount of air at atmospheric pressure.

If we put the balloon in a fridge, the gas inside gets cold, and the balloon shrinks, because both the amount of gas and its pressure remain constant.
If we make the balloon very cold, it will shrink and expand when it warms up.

The video shows how cooling and heating a gas affect its volume.

The effect of temperature on the volume of a confined gas at constant pressure can be seen in the following examples: The volume increases as the temperature increases, and decreases as the temperature decreases.

The temperature and volume are related for 1 mole of methane gas.

Volume and temperature are proportional if the temperature is inkelvin.
The line stops because methane liquefies at this temperature, and it intersects the graph's origin, representing a temperature of absolute zero.

Charles's law refers to the relationship between the volume and temperature of a given amount of gas at constant pressure.

A sample of carbon dioxide occupies 0.300 L.

This is a job for Charles's law because we are looking for the volume change caused by a temperature change at constant pressure.

Charles's law states that if the gas temperature is raised from 283 K to 301 K at a constant pressure, the volume will increase from 0.300 L to 0.321 L.

A sample of oxygen, O2, occupies 32.2 mL.

The temperature can be measured by observing the change in the volume of gas as the temperature changes.

When immersed in a mixture of ice and water, the volume of hydrogen in the hydrogen gas thermometer is 150.0 cm3.
The volume of hydrogen at the same pressure when immersed in boiling liquid ammonia is 131.7 cm3.
The temperature of boiling ammonia can be found on the kelvin and Celsius scales.

Charles's law states that a volume change caused by a temperature change should be used.

The temperature of the boiling ammonia on the Celsius scale is -34 degC.

A specific amount of air at a constant temperature is what the syringe contains.

If we keep the temperature constant, the gas in the syringe will be compressed into a smaller volume and the pressure will decrease if we pull out the plunger.

This example shows the effect of volume on the pressure of a confined gas.

Increasing the volume of a contained gas will increase its pressure.
If the volume increases by a certain factor, the pressure decreases by the same factor.

If the amount of gas and the temperature don't change, the gas exerts a lower pressure when it occupies a larger volume.

Graphs with curved lines are difficult to read at low or high values of the variables, and they are more difficult to use in fitting theoretical equations and parameters to experimental data.

Scientists try to find a way to linearize their data.

The relationship between volume and pressure is proportional.

The relationship between the volume and pressure of a given amount of gas was first published over 300 years ago.

The volume of gas held at constant temperature is related to the pressure under which it is measured.

The calculation will be as accurate as possible.

Respiration, or breathing, is the answer.

The gas laws apply here.
Your lungs take in gas that your body needs and excrete waste gas.

Lungs are made of stretchy tissue that expands and contracts while you breathe.

The intercostal muscles between your ribs contract when you inhale, making your lung volume larger.

Air enters the lungs from high pressure to low pressure.

The process reverses when you exhale, as your rib muscles relax and your lung volume decreases, causing the pressure in your lungs to increase.
You breathe in and out again and again, repeating this law cycle for the rest of your life.

Air is forced out of your lungs due to small pressure differences between your lungs and your surroundings.

The Italian scientist Amedeo Avogadro advanced a hypothesis in the 19th century to account for the behavior of gases.

You can investigate the relationships between pressure, volume, temperature, and amount of gas.

The simulation can be used to examine the effect of changing one parameter on another while holding the other parameters constant.

The most common values encountered are 0.08206 L atm mol-1 K-1 and 8.314 kPa L mol-1 K-1.

The calculations presented in this module assume ideal behavior for gases under low pressure and high temperature.

The ideal gas law can be used to calculate the fifth term if you specify any four of these terms.

Methane, CH4 is being considered for use as an alternative fuel.

A gallon of gasoline can be replaced with 655 g of CH4.

The amount must be in moles, the temperature must be inkelvin, and the pressure must be inm.

It would take about 1 atm of pressure to replace 1 gal of gasoline.

It requires a large container to hold enough methane to replace several gallons of gasoline.

The pressure in bar of 2520 moles of hydrogen gas in the 180-L storage tank of a modern hydrogen-powered car is calculated.

Scuba divers use compressed air to breathe.

A sample of ammonia is found to occupy 0.250 L in the laboratory.

Whether scuba diving at the Great Barrier Reef in Australia or in the Caribbean, divers must understand how pressure affects a number of issues related to their comfort and safety.

In order to avoid the risks associated with pressurized gases in the body, scuba divers must be aware of the amount of time they spend underwater.

The pressure changes rapidly as divers reach the surface.

The amount of pressures above the diver is what the pressure a diver experiences.
In the diving community, every 33 feet of salt water represents 1 ATA of pressure in addition to 1 ATA of pressure, which is expressed as "atmospheres absolute" in the book.
As a diver descends, the increase in pressure causes the body's air pockets in the ears and lungs to compress; on the ascent, the decrease in pressure causes these air pockets to expand, potentially rupturing eardrums or bursting the lungs.
Divers must add air to the body airspaces on the descent by breathing normally and adding air to the mask by breathing out of the nose, or they must release air from the body.
The ability to control whether a diver sinks or floats is controlled by theBCD.
If a diver ascends, the air in his BCD expands because of the lower pressure in the gases.
The diver begins to ascend when the air expands.
The diver needs to vent air from the BCD or risk a dangerous ascent.
In descending, the increased pressure causes the air in the BCD to compress and the diver sinks much more quickly, if they don't add air to the BCD or face much higher pressures near the ocean floor.
The pressure affects how long a diver can stay underwater.
If a diver dives 33 feet, the air will be compressed to one-half of its original volume because of the increased pressure.
The diver uses more air at the surface.

Changes in pressure and temperature can affect the volume of gas and the number ofoles in it.

Since the number of moles in a given volume of gas varies with pressure and temperature changes, chemists use standard temperature and pressure to report the properties of gases.

The study of the chemical behavior of gases was part of the basis of the most fundamental chemical revolution in history.

French noblemanAntoine Lavoisier changed chemistry from a qualitative to a quantitative science through his work with gases.
He discovered the law of matter, discovered the role of oxygen in combustion reactions, discovered the composition of air, and more.
He was guillotined during the French Revolution.
"It took the mob only a moment to remove his head, and a century will not suffice to reproduce it," said mathematician and astronomer Joseph-Louis Lagrange.
We can answer the question with a lot of solutions.

We can answer the question with volumes of gases.

The ideal gas equation can be used to relate the pressure, volume, temperature, and number of moles of a gas.
The ideal gas equation will be combined with other equations to find gas density and mass.
We will calculate amounts of substances in reactions involving gases.
This section will provide examples of applications and ways to integrate concepts we have already discussed, but will not introduce any new material or ideas.

The density of a gas will be determined if we can determine the mass of it.

The density of an unknown gas can be used to determine its mass.

A gas had a density of 0.0847 g/L and a pressure of 760 torr.

The density of a gas is determined by the number of moles of the gas in a liter and the pressure of the gas.

The gas densities are reported.

The composition of cyclopropane is composed of 85.7% carbon and 14.3% hydrogen.

The first thing to do is solve the empirical formula problem.

The percentage of each element should be converted into grams.
Determine the number of moles of hydrogen and carbon in the sample.
Divide the number of moles of carbon by the number of moles of hydrogen.

The Empirical formula is CH2 which is 14.03 g/empirical unit.

Acetylene is comprised of 92.3% C and 7.7% H by mass.

The determination of molar mass is a useful application of the ideal gas law.

The equation can be used to derive the mass of a gas.

A sample of the liquid in a flask with a tiny hole at the top can be turned into gas by heating it.

When the volatile liquid in the flask is heated past its boiling point, it becomes gas and drives air out of the flask.

The gas in the flask can be measured if it is cooled to room temperature.

A sample of chloroform gas weighing 0.494 g is collected in a flask with a volume of 129 cm3 when the atmospheric pressure is 742.1mm Hg.

120 g/mol is the atm x 0.129 L.

A sample of phosphorus that weighs 3.243 x 10-2 g exerts a pressure of 31.89 kPa in a 56.0-mL bulb.

Unless they react with each other, the individual gases in a mixture of gases don't affect each other's pressure.

Each individual gas in a mixture exerts the same pressure if it were alone in the container.

The total pressure of the mixture is 1350 kPa if equal-volume cylinders containing gas A at a pressure of 300 kPa, gas B at a pressure of 600 kPa, and gas C at a pressure of 450 kPa are all combined in the same-size cylinder.

A 10.0-L vessel has 2.50 x 10-3 mol of H2, 1.00 x 10-3 mol of He, and 3.00 x 10-4 mol of Ne.

This is an example of a mole fraction calculation.

Oxygen, O2, and N2O are contained in a gas mixture used for anesthesia.

The pressure of the mixture is 192 kPa.

A bottle filled with water and inverted into a dish filled with water can be used to collect gases that don't react with water.

The bottle's pressure can be adjusted by raising or lowering it.
The pressure of the gas is equal to the atmospheric pressure when the water level is the same inside and outside the bottle.

When a reaction produces a gas that is collected above water, the trapped gas is a mixture of the gas produced by the reaction and water vapor.

If the collection flask is positioned to equalize the water levels both within and outside the flask, the pressure of the trapped gas mixture will equal the atmospheric pressure outside the flask.

When we measure the pressure of the gas by this method, there is more than one factor to consider.

There is always water above a sample of liquid water.
As a gas is collected over water, it becomes saturated with water vapor and the total pressure of the mixture equals the partial pressure of the gas plus the partial pressure of the water vapor.
The pressure of the pure gas is equal to the total pressure minus the pressure of the water vapor, which is referred to as the "dry" gas pressure.

The vapor pressure of water at sea level is shown in the graph.

The relationship between reactants and products in chemical reactions is described in chemical snohiometry.

We can now use gas volumes to indicate the quantities of reactants and products we have previously measured.

The ideal gas equation can be used to calculate how many moles of the gas are present.
We can calculate the volume of a gas at any temperature and pressure if we know how many moles are involved.

Sometimes we can take advantage of a simplified feature of the stoichiometry of gases that do not exhibit ideal behavior: All gases that show ideal behavior contain the same number of molecules in the same volume.

The coefficients in the equation for the reaction are used to give the ratios of gases involved in a chemical reaction.

The volume of a gas is directly proportional to the number of moles of the gas, if all gas volumes are measured at the same.

Avogadro's law states that equal volumes of N2, H2, and NH3 at the same temperature and pressure contain the same number of molecules.

The volume of H2 required is three times the volume of N2, and the volume of NH3 produced is two times the volume of N2.

Two volumes of NH3 are formed by combining one volume of N2 with three volumes of H2.

It is assumed that the propane undergoes complete combustion.

A volume of O2 will be required to react with C3H8.

9340 L of acetylene gas, C2H2, is provided by an acetylene tank for an oxyacetylene welding torch.

Ammonia is an important chemical.

A volume of 683 billion cubic feet of ammonia, measured at 25 degC and 1 atm, would be manufactured.

The ratio of the volumes of H2 and NH3 will be 3:2 because they contain equal numbers of molecule and each three molecule of H2 that reacts produce two molecule of NH3.

CO2 and water vapor are products.

Sulfur dioxide is used in the preparation of sulfuric acid.

The thin skin of our atmosphere keeps the earth from being an ice planet.

This is due to less than 1% of the air molecule.
Almost 13 of the energy from the sun that reaches the earth is reflected back into space, with the rest absorbed by the atmosphere and the surface of the earth.
Some of the energy that the earth absorbs is re-emitted asIR radiation, a portion of which goes back out through the atmosphere into space.
Most of the IR radiation is absorbed by substances in the atmosphere, known as greenhouse gases, which trap some of the heat.
Without the atmosphere, the global average temperature would be about -19 degC.
Water vapor, carbon dioxide, methane, and ozone are greenhouse gases.

The greenhouse effect is when greenhouse gases trap enough of the sun's energy to make the planet habitable.

Warming the planet and causing more extreme weather events are caused by human activities.

Fossil fuel burning is one of the main causes of the recent increase in CO2 in the atmosphere.

According to reliable data from ice cores, CO2 concentration in the atmosphere is at the highest level in the past 800,000 years, and other evidence indicates that it may be at its highest level in 20 million years.
In the last few years, the CO2 concentration has increased from below 300 to almost 400 parts per million.

Over the past 700,000 years, CO2 levels ranged from 200-300 parts per million, with a steep increase over the past 50 years.

The video explains greenhouse gases and global warming.

She has written many important papers on climate change and helped determine and explain the cause of the ozone hole.

She is a member of the National Academy of Sciences, the Royal Society, the French Academy of Sciences, and the European Academy of Sciences, and has been awarded the top scientific honors in the US and France.
She used to be a professor at the University of Colorado and is now at MIT.