GS_Gas Laws Lesson

Gas Laws

Now that you know the proper units for measuring pressure, volume, and temperature of a gas, let's explore the relationships between them. We will begin by looking at the simple relationships between each pair of these variables. Collectively, these relationships are known as the gas laws. We will use look at several animations (shown as a still image below) to explore these relationships. When looking at an animation or any visual, you first need to orient yourself with what the image is showing you. I will walk you through this one, but you will eventually have to do this on your own for other visuals!

The set up shows a theoretical gas confined in a blue container with an adjustable volume (like the adjustable volume of a syringe used to dispense medication). Focus your attention on the gas particles in the yellow area. The measured quantities will represent the gas in the yellow area. This is where the experiments take place, not the light blue area on the left.

Theoretical Gas Confined image with mass, pressure, temperature, and volume labelledVolume

  • The volume of the container is represented in yellow and measured in m3 on the right side of the container.
  • The volume can be adjusted by changing the position of the red piston (see A).

Temperature

  • The temperature is shown in Kelvin (see B).
  • The temperature can be adjusted using the flame.

Pressure 

  • The pressure is measured in atm (see C).
  • The pressure can be adjusted by adding or removing the green weights.

Number of particles

  • The number of moles of the gas in the experiment are represented by the black dots in the yellow area.
  • The number of gas molecules can be changed by inserting or removing gas molecules from the light blue container labeled mass (see D).

Volume - Pressure Relationship

To understand the relationship between a pair of variables, all other variables must be held constant. In the animation below, notice that the temperature and the number of moles (shown as mass) are held constant so that we can see the relationship between volume and temperature.

Watch below to see what happens to the volume as more green weights are added.

as more green weights are added, pressure causes the volume to decrease

Adding more weights increases the pressure  on the gas. This causes the volume to decrease. This relationship, where one variable increases as the other decreases, is an inverse proportion.   This inverse relationship between pressure and volume of a gas was first determined by Robert Boyle (1627 - 1691), and is now known as Boyle's Law or the pressure-volume law. We typically do not use a symbol to represent inverse proportions. So, to express inverse relationships between variables, we use the symbol for a direct proportion (α) and write the reciprocal for one of the variables, as shown below.

BOYLE'S LAW Ρα (1 / V) Pressure of a gas is inversely proportional to its volume when temperature and amount of gas are held constant.

Go back up and observe the graph of volume versus pressure. When you graph two variables with an inverse relationship, the shape of the graph is a curve, specifically a hyperbola.

Temperature - Volume Relationship

In the animation below, the different variables are held constant than before. Here, pressure and number of molecules are held constant. The heat source is turned off and the gas is allowed to cool. As a result, the volume of the gas changes.

gif depicting weights being removed and pressure decreases, so volume increases

Watch the temperature gauge and the resulting change in volume. As the temperature of the gas decreases, the volume of the gas decreases . This is a direct proportion. Look at the graph above that shows this relationship. The graph of a direct proportion is a direct proportion graph .

This direct relationship between temperature and volume of a gas was determined by Jacques Charles (1746 - 1823).   He was a French mathematician who was highly interested in hot air balloons.   During this work, he developed the relationship between volume and temperature of a gas when the amount of gas and pressure are both fixed. This became known as  Charles' law  or the temperature-volume law.

CHARLES' LAW Tav Temperature of a gas is directly proportional to its volume when pressure and amount of gas are held constant.

Pressure - Temperature Relationship

In the animation below, volume and number of molecules are held constant. The heat source is turned off and the gas is allowed to cool. As a result, the pressure of the gas changes.

gif depicting pressure decreases, temperature decreasing, and the pressure becomes a line increasing

Watch the temperature gauge and the resulting change in pressure.   As the temperature of the gas decreases, the pressure of the gas decreases . This is  direct proportion whose graph is a line .

This direct relationship between temperature and pressure of a gas was determined by Joseph Louis Gay-Lussac (1778 - 1850), another Frenchman.   He was a scientist that developed Charles' work further.   He determined that the pressure of a fixed amount of gas at a constant volume varies directly with its Kelvin temperature, known as  Gay-Lussac's law  or the pressure-temperature law.

GAY-LUSSAC'S LAW Рат Pressure of a gas is directly proportional to its temperature when volume and amount of gas are held constant.

Remember to work on the module practice problems as you complete each section of content.  

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