Unit 6 - Investigating the relationship between pressure and volume in a gas
Introduction and historical background
Investigating the relationship between pressure and volume of a gas, Robert Boyle was a natural philosopher
and theological writer, he’s best-known for his discovery of one of the first gas laws-relating the pressure of a
gas to its volume; he established that electrical forces are transmitted through a vacuum, but sound is not; and
he also stated that the movement of particles is responsible for heat [1]. Boyle’s law states that for a gas at
constant temperature, pressure x volume is also constant. So increasing the pressure of a gas means that volume
will decrease ensuring that the temperature remains constant. When temperature is increasing, the gas particles
move faster and the collisions become stronger and more frequent. Meaning that pressure also rises, however
when temperature falls, the gas particles move more slowly and the collisions are softer and less frequent.
Eventually at absolute zero, which is -273 °C, the molecules stop moving and the gas does not exert any
pressure at all.This is known as absolute zero [2].This means that the pressure also falls. Charles law and
Gays-Lussac's law links with boyes law in terms of temperature, volume and pressure. Charles law states that
the volume of a given amount of gas is held at constant pressure directly proportional to the kelvin
temperature, so when volume rises, the temperature also increases. Gays-Lussac's law states that pressure of a
given amount of gas held at constant volume is directly proportional to the kelvin temperature, when there’s an
increase in temperature, the pressure increases [3].
When the volume decreases, the pressure increases. This shows that the pressure of a gas is inversely
proportional to its volume. This is shown in Boyles Law :
● P1V1 = P2V2
o P1 is the initial pressure
o V1 is the initial volume
o P2 is the final pressure
o V2 is the final volume
● Pressure 1 x volume 1 = pressure 2 x volume2
o Volume measured as meters cubed (m3)
o Temperature measured as temperature in Kelvin (k)
This means that a gas at a constant temperature, pressure x volume is also constant. So, increasing pressure
from pressure 1 to pressure 2 means volume will change to volume 2, providing the temperature remains
constant.
Boyle's law is based on experiments with air, which he considered to be a fluid of particles at inbetween small
invisible springs. At that time, air was still seen as one of the four elements, but Boyle disagreed. Boyles
interest was probably to understand air as an essential element of life [4]. This is reliable as this information
originated from boyles archives that were published in 1992. To test this theory he used a j-shaped tube and
once we poured mercury from one side, he pushed the air on the other side to compact under pressure of
mercury. He repeated this experiment a couple times and used varied amounts of mercury he realised that under
controlled conditions, the pressure of a gas is inversely proportional to the volume occupied by it [5], This is
reliable as Britannica publication is known as a credible source, consisting of legitimate science or are based
through the use of credible scientific sourcing.
Boyle's law is often used as a way to partially explain how breathing in the human body works. Usually
demonstrates how lung volume may be increased or decreased, which creates a lower or higher air pressure
within the lungs.This forms pressure difference between the air inside the lungs and the environment air
pressure, which in turn triggers either inhalation or exhalation as air moves from high to low pressure[6].
, [7]
Fig 1.
Depiction of what
would happen inside
of a lung using boyles
law, caused by
respiration.
Limitations of Boyle's law
- Boyle's law is applicable only to ideal gases
- The law holds good only at very high temperature and low pressure
- The law fails at high pressures. The product but shows a slight increase in pressure. This increase is due
to an increase in the volume which is caused by repulsive forces among the molecules. At high
pressures , the molecules are too slow to one another. Repulsive forces become dominant as
compactness increases. This results in the expansion of the gas.
Types of variables within this investigation
Temperature
Temperature is a physical quantity that shows hot and cold. It is the representation of thermal energy, which is a
source of heat. It is almost always measured with thermometers, which are put in various temperature scales.
The most common being celsius scale, fahrenheit scale and the kelvin scale. The lowest temperature known to
us is absolute zero, meaning no more thermal energy can be extracted, Commonly recognized in the third law
of thermodynamics which states “the entropy of a system approaches a constant value as its temperature
approaches absolute zero”. Temperature is essential in fields of natural science, ecology etc. as well as aspects
of daily life. Most physical processes are related to temperature such as density, solubility, vapor pressure, the
rate and extent to which chemical reactions occur [8, the amount and characteristics of thermal radiation emitted
from the surface of an object, and the speed of sound which is a function of the square root of the absolute
temperature[[9]. Celsius is an empirical scale that was developed, which led to its zero point 0 °C being defined
by the freezing point of water, and more degrees defined so that 100 °C was boiling point of water. For this
investigation temperature is a controlled variable, this is what is kept the same throughout the experiment. Any
change in a control variable in an experiment would invalidate the correlation of the dependent variable to the
independent variable, causing a great fault.
Volume
Volume is the quantity of three dimensional space enclosed by a closed surface, eg. the space that a substance
or shape occupies[10]. It is normally calculated numerically using SI derived units ( units of measurement
derived from the seven base units founded by international systems of units), the cubic meter. Generally, the
volume of a container is understood to be the capacity of the container, the amount of fluid that it can hold,
rather than the amount of space the container itself removed. In thermodynamics, the volume, an intensive
property, is the system's volume per unit mass. Volume is a functional state and is interdependent with other
thermodynamic properties such as pressure and temperature. The dependent variable is the variable being tested
and measured in an experiment and is dependent on the independent variable[11]
Pressure
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is
distributed [12] (a measure of how much force is acting on an area) Various units express pressure, some come
from a unit of force divided by a unit of area; the pascal (Pa), pressure may also be shown in terms of standard
Introduction and historical background
Investigating the relationship between pressure and volume of a gas, Robert Boyle was a natural philosopher
and theological writer, he’s best-known for his discovery of one of the first gas laws-relating the pressure of a
gas to its volume; he established that electrical forces are transmitted through a vacuum, but sound is not; and
he also stated that the movement of particles is responsible for heat [1]. Boyle’s law states that for a gas at
constant temperature, pressure x volume is also constant. So increasing the pressure of a gas means that volume
will decrease ensuring that the temperature remains constant. When temperature is increasing, the gas particles
move faster and the collisions become stronger and more frequent. Meaning that pressure also rises, however
when temperature falls, the gas particles move more slowly and the collisions are softer and less frequent.
Eventually at absolute zero, which is -273 °C, the molecules stop moving and the gas does not exert any
pressure at all.This is known as absolute zero [2].This means that the pressure also falls. Charles law and
Gays-Lussac's law links with boyes law in terms of temperature, volume and pressure. Charles law states that
the volume of a given amount of gas is held at constant pressure directly proportional to the kelvin
temperature, so when volume rises, the temperature also increases. Gays-Lussac's law states that pressure of a
given amount of gas held at constant volume is directly proportional to the kelvin temperature, when there’s an
increase in temperature, the pressure increases [3].
When the volume decreases, the pressure increases. This shows that the pressure of a gas is inversely
proportional to its volume. This is shown in Boyles Law :
● P1V1 = P2V2
o P1 is the initial pressure
o V1 is the initial volume
o P2 is the final pressure
o V2 is the final volume
● Pressure 1 x volume 1 = pressure 2 x volume2
o Volume measured as meters cubed (m3)
o Temperature measured as temperature in Kelvin (k)
This means that a gas at a constant temperature, pressure x volume is also constant. So, increasing pressure
from pressure 1 to pressure 2 means volume will change to volume 2, providing the temperature remains
constant.
Boyle's law is based on experiments with air, which he considered to be a fluid of particles at inbetween small
invisible springs. At that time, air was still seen as one of the four elements, but Boyle disagreed. Boyles
interest was probably to understand air as an essential element of life [4]. This is reliable as this information
originated from boyles archives that were published in 1992. To test this theory he used a j-shaped tube and
once we poured mercury from one side, he pushed the air on the other side to compact under pressure of
mercury. He repeated this experiment a couple times and used varied amounts of mercury he realised that under
controlled conditions, the pressure of a gas is inversely proportional to the volume occupied by it [5], This is
reliable as Britannica publication is known as a credible source, consisting of legitimate science or are based
through the use of credible scientific sourcing.
Boyle's law is often used as a way to partially explain how breathing in the human body works. Usually
demonstrates how lung volume may be increased or decreased, which creates a lower or higher air pressure
within the lungs.This forms pressure difference between the air inside the lungs and the environment air
pressure, which in turn triggers either inhalation or exhalation as air moves from high to low pressure[6].
, [7]
Fig 1.
Depiction of what
would happen inside
of a lung using boyles
law, caused by
respiration.
Limitations of Boyle's law
- Boyle's law is applicable only to ideal gases
- The law holds good only at very high temperature and low pressure
- The law fails at high pressures. The product but shows a slight increase in pressure. This increase is due
to an increase in the volume which is caused by repulsive forces among the molecules. At high
pressures , the molecules are too slow to one another. Repulsive forces become dominant as
compactness increases. This results in the expansion of the gas.
Types of variables within this investigation
Temperature
Temperature is a physical quantity that shows hot and cold. It is the representation of thermal energy, which is a
source of heat. It is almost always measured with thermometers, which are put in various temperature scales.
The most common being celsius scale, fahrenheit scale and the kelvin scale. The lowest temperature known to
us is absolute zero, meaning no more thermal energy can be extracted, Commonly recognized in the third law
of thermodynamics which states “the entropy of a system approaches a constant value as its temperature
approaches absolute zero”. Temperature is essential in fields of natural science, ecology etc. as well as aspects
of daily life. Most physical processes are related to temperature such as density, solubility, vapor pressure, the
rate and extent to which chemical reactions occur [8, the amount and characteristics of thermal radiation emitted
from the surface of an object, and the speed of sound which is a function of the square root of the absolute
temperature[[9]. Celsius is an empirical scale that was developed, which led to its zero point 0 °C being defined
by the freezing point of water, and more degrees defined so that 100 °C was boiling point of water. For this
investigation temperature is a controlled variable, this is what is kept the same throughout the experiment. Any
change in a control variable in an experiment would invalidate the correlation of the dependent variable to the
independent variable, causing a great fault.
Volume
Volume is the quantity of three dimensional space enclosed by a closed surface, eg. the space that a substance
or shape occupies[10]. It is normally calculated numerically using SI derived units ( units of measurement
derived from the seven base units founded by international systems of units), the cubic meter. Generally, the
volume of a container is understood to be the capacity of the container, the amount of fluid that it can hold,
rather than the amount of space the container itself removed. In thermodynamics, the volume, an intensive
property, is the system's volume per unit mass. Volume is a functional state and is interdependent with other
thermodynamic properties such as pressure and temperature. The dependent variable is the variable being tested
and measured in an experiment and is dependent on the independent variable[11]
Pressure
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is
distributed [12] (a measure of how much force is acting on an area) Various units express pressure, some come
from a unit of force divided by a unit of area; the pascal (Pa), pressure may also be shown in terms of standard
