What causes the pressure to increase if more gas particles are added to a closed container?

Pressure What causes gas pressure in a closed container? Pressure is the result of a force distributed over an area. Collisions between particles of a gas and the walls of the container cause the pressure in a closed container of gas.

Pressure A moving hockey puck exerts pressure on any object it hits. A layer of shatterproof glass protects spectators. The faster the puck is traveling, the greater the force of the puck on the glass. A greater force means more pressure. The smaller the area of impact is, the greater the pressure. If the edge of the puck hits the glass, it exerts more pressure than if the face of the puck hits the glass.

The SI unit of pressure is derived from SI units for force and area. Force is measured in newtons (N). Area is measured in square meters (m2). The SI unit for pressure, the pascal (Pa), is shorthand for newtons per square meter. Scientists often express larger amounts of pressure in kilopascals. One kilopascal (kPa) is equal to 1000 pascals.

Factors That Affect Gas Pressure What factors affect gas pressure? Factors that affect the pressure of an enclosed gas are its temperature, its volume, and the number of its particles.

Factors That Affect Gas Pressure Temperature Raising the temperature of a gas will increase its pressure if the volume of the gas and the number of particles are constant.

Factors That Affect Gas Pressure Volume Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant.

Factors That Affect Gas Pressure Number of Particles Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant. The more particles there are in the same volume, the greater the number of collisions and the greater the pressure.

Charles’s Law French physicist Jacques Charles collected data on the relationship between the temperature and volume of gases. The graph of the data showed a direct relationship between the volume of a gas and the temperature of the gas.

Charles’s Law Charles extended the graph beyond the measured data to find the temperature that would produce a volume of 0 L. The temperature at the point where the line crossed the x-axis was –273.15°C.

Charles’s Law Charles extended the graph beyond the measured data to find the temperature that would produce a volume of 0 L. The temperature at the point where the line crossed the x-axis was –273.15°C.

Charles’s Law This temperature is equal to 0 K on the Kelvin temperature scale. A temperature of 0 K is called absolute zero.

Charles’s Law Charles’s law states that the volume of a gas is directly proportional to its temperature in kelvins if the pressure and the number of particles of the gas are constant. T1 and V1 represent the temperature and volume of a gas before a change occurs. T2 and V2 represent the temperature and volume after a change occurs.

Boyle’s Law Robert Boyle described the relationship between the pressure and volume of a gas. The graph shows an inverse relationship between the volume of a gas and the pressure of the gas.

Boyle’s Law Robert Boyle described the relationship between the pressure and volume of a gas. The graph shows an inverse relationship between the volume of a gas and the pressure of the gas.

Boyle’s Law Boyle’s law states that the volume of a gas is inversely proportional to its pressure if the temperature and the number of particles are constant. P1 and V1 represent the pressure and volume of a gas before a change occurs. P2 and V2 represent the pressure and volume of a gas after a change occurs.

The Combined Gas Law The relationships described by Boyle’s law and Charles’s law can be described by a single law. The combined gas law describes the relationship among the temperature, volume, and pressure of a gas when the number of particles is constant.

The Combined Gas Law The Combined Gas Law A cylinder that contains air at a pressure of 100 kPa has a volume of 0.75 L. The pressure is increased to 300 kPa. The temperature does not change. Find the new volume of air.

The Combined Gas Law Read and Understand What information are you given? P1 = 100 kPa P2 = 300 kPa V1 = 0.75 L

The Combined Gas Law Plan and Solve What unknown are you trying to calculate? What expression can you use?

The Combined Gas Law Plan and Solve What unknown are you trying to calculate? What expression can you use?

The Combined Gas Law Plan and Solve Cancel out the variable that does not change and rearrange the expression to solve for V2. Replace each variable with its known value.

The Combined Gas Law Plan and Solve Cancel out the variable that does not change and rearrange the expression to solve for V2. Replace each variable with its known value.

The Combined Gas Law Look Back and Check Is your answer reasonable?

The Combined Gas Law Look Back and Check Is your answer reasonable? Volume should decrease as pressure increases. The pressure tripled from 100 kPa to 300 kPa. The answer, 0.25 L, is one third the original volume, 0.75 L.

The Combined Gas Law 1. A gas has a volume of 5.0 L at a pressure of 50 kPa. What happens to the volume when the pressure is increased to 125 kPa? The temperature does not change.

The Combined Gas Law 2. Gas stored in a tank at 273 K has a pressure of 388 kPa. The safe limit for the pressure is 825 kPa. At what temperature will the gas reach this pressure?

The Combined Gas Law 3. At 10ºC, the gas in a cylinder has a volume of 0.250 L. The gas is allowed to expand to 0.285 L. What must the final temperature be for the pressure to remain constant? (Hint: Convert from degrees Celsius to kelvins using the expression ºC + 273 = K.)

The Combined Gas Law Balloons like this one are used by scientists to gather data about Earth’s atmosphere. The balloon is filled with hydrogen or helium. It carries a package of weather instruments up into the atmosphere.

The Combined Gas Law The gas laws explain the behavior of the gas in the balloon.

Assessment Questions What causes the pressure to increase if more gas particles are added to a closed container? an increase in the number of collisions between the gas and the container walls a decrease in the volume of the container a decrease in the size of each particle as the number of particles increases an increase in the number of collisions between air particles and the outside of the container

Assessment Questions What causes the pressure to increase if more gas particles are added to a closed container? an increase in the number of collisions between the gas and the container walls a decrease in the volume of the container a decrease in the size of each particle as the number of particles increases an increase in the number of collisions between air particles and the outside of the container ANS: A

Assessment Questions When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease? increase in air temperature decrease in the balloon's volume decrease in the number of air particles as they leaked out of the balloon a chemical reaction between the air particles and the balloon

Assessment Questions When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease? increase in air temperature decrease in the balloon's volume decrease in the number of air particles as they leaked out of the balloon a chemical reaction between the air particles and the balloon ANS: C

Assessment Questions A gas has a volume of 15 L, a temperature of 300 K, and an unknown initial pressure. Then, the gas expands to 30 L, remains at 300 K, and has a pressure of 300 kPa. What was the initial pressure of the gas? 150 kPa 600 kPa 330 kPa 570 kPa

Assessment Questions A gas has a volume of 15 L, a temperature of 300 K, and an unknown initial pressure. Then, the gas expands to 30 L, remains at 300 K, and has a pressure of 300 kPa. What was the initial pressure of the gas? 150 kPa 600 kPa 330 kPa 570 kPa ANS: B

Assessment Questions According to Charles’s law, the relationship between the temperature and the volume of a gas is direct. inverse. exponential. inverse square.

Assessment Questions According to Charles’s law, the relationship between the temperature and the volume of a gas is direct. inverse. exponential. inverse square. ANS: A

Assessment Questions When the temperature of the gas in closed container is increased, the pressure increases. True False

Assessment Questions When the temperature of the gas in closed container is increased, the pressure increases. True False ANS: T

Gas is a state of matter that has no fixed shape and no fixed volume. Gases have a lower density than other states of matter, such as solids and liquids. There is a great deal of empty space between particles, which have a lot of kinetic energy and aren’t particularly attracted to one another. Gas particles move very fast and collide with one another, causing them to diffuse, or spread out until they are evenly distributed throughout the volume of the container. 

According to the educational website Lumen Learning (opens in new tab) gas can only be contained by either being fully surrounded by a container or held together by gravity.

When more gas particles enter a container, there is less space for the particles to spread out, and they become compressed. The particles exert more force on the interior volume of the container. This force is called pressure. There are several units used to express pressure. Some of the most common are atmospheres (atm), pounds per square inch (psi), millimeters of mercury (mmHg) and pascals (Pa). The units relate to one another this way: 1 atm = 14.7 psi = 760 mmHg = 101.3 kPa (1,000 pascals).

Related: Greenhouse gases: Causes, sources and environmental effects 

A gas can be converted to a liquid through compression at a suitable temperature, according to Purdue University (opens in new tab). But if the critical temperature is reached, the vapor cannot be liquified regardless of how much pressure is applied. Critical pressure is the pressure needed to liquefy a gas at its critical temperature.

Examples of critical temperatures and pressure of different substances according to Engineering Toolbox (opens in new tab) 

Measurable properties of gases

Besides pressure, denoted in equations as P, gases have other measurable properties: temperature (T), volume (V) and number of particles, which is expressed in a mole number (n or mol). In work involving gas temperature, the Kelvin scale is often used. 

Because temperature and pressure vary from place to place, scientists use a standard reference point, called standard temperature and pressure (STP), in calculations and equations. Standard temperature is the freezing point of water — 32 degrees Fahrenheit (0 degrees Celsius, or 273.15 Kelvin). Standard pressure is one atmosphere (atm) — the pressure exerted by the atmosphere on Earth at sea level. 

Gas laws

Temperature, pressure, amount and volume of a gas are interdependent, and many scientists have developed laws to describe the relationships among them. 

Boyle's law

Named after Robert Boyle, who first stated it in 1662. Boyle's law states that if the temperature is held constant, volume and pressure have an inverse relationship; that is, as volume increases, pressure decreases, according to the University of California, Davis' ChemWiki (opens in new tab).

Increasing the amount of space available will allow the gas particles to spread farther apart, but this reduces the number of particles available to collide with the container, so pressure decreases. 

Decreasing the volume of the container forces the particles to collide more often, so the pressure is increased. A good example of this is when you fill a tire with air. As more air goes in, the gas molecules get packed together, reducing their volume. As long as the temperature stays the same, the pressure increases.

Charles' law (Gay-Lussac's law)

In 1802, Joseph Louis Gay-Lussac, a French chemist and physicist referenced data gathered by his countryman, Jacque Charles, in a paper describing the direct relationship between the temperature and volume of a gas kept at a constant pressure. Most texts refer to this as Charles' law, but a few call it Gay-Lussac's law, or even the Charles Gay-Lussac law. 

This law states that the volume and temperature of a gas have a direct relationship: As temperature increases, volume increases when pressure is held constant. Heating a gas increases the kinetic energy of the particles, causing the gas to expand. In order to keep the pressure constant, the volume of the container must be increased when a gas is heated. 

This law explains why it is an important safety rule that you should never heat a closed container. Increasing temperature without increasing the volume available to accommodate the expanding gas means that pressure builds up inside the container and may cause it to explode. The law also explains why a turkey thermometer pops out when the turkey is done: The volume of air trapped under the plunger increases as the temperature inside the turkey climbs.

Avogadro's number

In 1811, Italian scientist Amedeo Avogadro proposed the idea that equal volumes of gas at the same temperature and pressure will have an equal number of particles, regardless of their chemical nature and physical properties.  

Ideal gas constant

The kinetic energy per unit of temperature of one mole of a gas is a constant value, sometimes referred to as the Regnault constant, named after the French chemist Henri Victor Regnault (opens in new tab). It is abbreviated by the letter R. Regnault studied the thermal properties of matter and discovered that Boyle's law was not perfect. When the temperature of a substance nears its boiling point, the expansion of the gas particles is not exactly uniform. 

Ideal gas law

Avogadro's Number, the ideal gas constant, and both Boyle's and Charles' laws combine to describe a theoretical ideal gas in which all particle collisions are absolutely equal. The laws come very close to describing the behavior of most gases, but there are very tiny mathematical deviations due to differences in actual particle size and tiny intermolecular forces in real gases. Nevertheless, these important laws are often combined into one equation known as the ideal gas law. Using this law, you can find the value of any of the other variables — pressure, volume, number or temperature — if you know the value of the other three. 

Additional resources

Learn more about supercritical fluids and their uses with this article from SciMed (opens in new tab). For quick children-friendly facts about gases head over to the educational website Love My Science (opens in new tab). Discover more examples of gases with this informative material from the educational website Science Notes (opens in new tab).  

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