Chemistry Gas Laws: Videos & Practice Problems

The chemistry gas laws describe the relationships between pressure, volume, and temperature of gases. Boyle's law states that volume and pressure are inversely proportional, while Gay Lussac's law indicates that pressure and temperature are directly proportional. Avogadro's law connects volume and moles directly, and Charles's law shows that volume and temperature are also directly proportional. Key equations include $p^{1}v=p^{2}v$ for Boyle's law and $p^1/t^1=p^2/t^2$ for Gay Lussac's law.

Chemistry Gas Laws

The chemistry gas laws are laws that relate together the pressure, volume, and temperature of a gas. Now we're going to say here that they can be derived from the ideal gas law. Remember, your ideal gas law is PV=nRT. And to remember your 4 chemistry gas laws, just remember, be great at chemistry.

The first chemistry gas law B is Boyle's law. Boyle's law looks at the relationship between volume and pressure. G stands for Gay Lussac's law. It relates together pressure and temperature. A is for Avogadro's law. Avogadro's law looks at volume and moles. And then finally C, C stands for Charles' law, which relates together volume and temperature.

Now that we have chemistry gas laws connected to these pairings, let's take a look at the series of videos where we go in greater depths with each one of these chemistry gas laws.

Chemistry Gas Laws

Boyle's law states that volume and pressure are inversely proportional at constant moles and temperature. It's named after Robert Boyle and it illustrates how the volume of a container is greatly affected by pressure changes. Now, how do we depict this relationship? When we say they're inversely proportional, we can say that they're on different levels. So we're going to say volume is inversely proportional to pressure, which means that V ∝ 1P. This shows our inverse relationship between volume and pressure. Think of it as volume being a numerator, and pressure being a denominator. They're on different levels, so they are different from one another. If one goes up, the other one has to go down.

Now, this is illustrated if we take a look at variables. Here we have two containers with movable pistons. Volume is just the space within my container. So, if we look at this image we can say that the volume is pretty high. Pressure represents the downward force that we have on the piston. Now, the downward force on the piston must be pretty low, which is why the piston hasn't slid down lower. Here we can see volume is high, pressure is low. Now, let's say that we garnered enough force from the pressure we're able to push down on this piston. We can see that the volume now is smaller, so the volume now is low and that's a direct result of the pressure being higher.

Now, how do we depict this inverse relationship graphically? Well, to show an inverse relationship between two variables, you would show it like this. This graph is showing me that my volume is decreasing over time and as a result, the pressure is increasing over time. This is how we depict an inverse relationship between two variables.

Now, how do we show Boyle's law formula in the form of a digested formula? Here we'd say that it becomes P₁V₁ = P₂V₂. This represents our adjusted formula, also our Boyle's law formula where P₁ is our initial pressure, V₁ is our initial volume, P₂ is our final pressure, and V₂ is our final volume. Now remember, we went over how we derived these different types of formulas under the ideal gas laws application section. If you don't know what that is or if you haven't seen those videos yet, I suggest you go back and take a look at how we can derive this formula. Now we just know that it's connected to Boyle's law and therefore called the Boyle's law formula. So keep this in mind. Boyle's law says that pressure and volume are inversely proportional, meaning if one is high the other one would be low.

Chemistry Gas Laws

Now, Gay Lussac's law, also known as Amaton's law, says that pressure and temperature are directly proportional at constant moles n and volume v. As the temperature increases, our gas particles collide with the walls more rapidly. That's because they're absorbing the thermal energy and using it to propel themselves faster inside the container. This will cause an increase in my pressure. Remember, pressure itself equals force over the area. We said that the volume is constant, so your area would be constant; it's staying the same. If I'm increasing my temperature, my gas will move faster inside the container, they're going to hit the walls more rapidly but also with more force. So my force is increasing, my area is staying the same, causing my pressure to increase. This is why pressure and temperature are directly proportional. Remember that with all gas law calculations, we must use the SI units for temperature in Kelvin.

Now, what is the pressure-temperature relationship? They're directly proportional, so you just say that p is directly proportional to t, and that happens when moles and volume are fixed. To illustrate this, imagine two images of containers with movable pistons. In the first image, a heat source is not applied, so the temperature here would be low. The molecules don't have extra outside energy to absorb, so they're not moving as vigorously and rapidly. They're not hitting the container with as much force, and therefore our pressure would be low. But when I add a flame, the container absorbs the heat which eventually transitions to the molecules absorbing this heat, allowing them to move more rapidly and with greater force. So the temperature is high, which eventually leads to greater force, which leads to greater pressure. Pressure would be high. How would I depict this in a plot? They're both directly proportional so we'd say that they both would be increasing together so you'd have a line that's increasing over time.

What would their adjusted formula be or the Gay Lussac's formula? It would just be p₁ / t₁ = p₂ / t₂. Take a look at my ideal gas law applications section on how we could derive this formula. Remember, with these variables we'd say initial pressure is p₁, initial temperature is t₁, final pressure will be p₂, and final temperature will be t₂. Remember when discussing Gay Lussac's law or Amaton's law that pressure and temperature are directly proportional when our moles n and our volume v are constant or fixed.

Chemistry Gas Laws

Avogadro's law states that our volume V and our moles n are directly proportional at constant pressure p and temperature t. It's named after Amedeo Avogadro and it shows that the volumes of gases are connected to their number of molecules. Here, we're going to say that the relationship between volume and moles is that V is directly proportional to moles, and again it happens when p and t are constant or fixed. The way we depict this with our movable pistons is if we take a look here at this image, we're going to say this container has a lot of dots, so it has a lot of moles or number of molecules. So moles would be high. To house all of these molecules we'd want our volume to be high, because gases like it when there's an optimal amount of distance between them. But what happens if I take some of these molecules of gases out? Well, our moles of gas would be low, and I no longer need as much space for them so my volume would be low. They both are high together or low together when pressure and temperature are constant or fixed. Now, how do we depict this in a plot? Since they're directly proportional, you'd say this line of V and n would show it increasing over time. Where you could start out at 0 liters and it increases over time as our moles increase.

Now, what would our adjusted formula or our Avogadro's Law formula be? That would just be V1n1 = V2n2. So our initial variables here, initial moles would be n1 initial volume V1. Final moles would be n2 final volume would be V2. So just remember our volume and moles are directly proportional, meaning they're both high together or low together when our pressure and temperature are constant or fixed.

Chemistry Gas Laws

Charles' law states that volume and temperature are directly proportional at constant moles n and pressure p. It's named after Jacques Charles and it illustrates how the volume of a container is greatly affected by volume. Here to show this direct proportionality between volume and temperature, we just say V is directly proportional to T when our moles n and pressure p are constant or fixed. If we were to illustrate this with movable pistons, if we take a look here we'd say that in this first image, our volume is low and we haven't applied any temperature or heat to this container, I mean, so the temperature would be low. Here, I'm applying a flame to this. This is going to cause a higher temperature. And what's happening here is because the piston is movable and the pressure is constant, our gas particles are gaining enough outside energy to basically hit all corners of this container including the movable piston up and that's what caused the volume to also expand. So our volume is high. How do we illustrate this direct proportionality between volume and temperature? Well, we'd say here that they're both increasing or decreasing together. So you can illustrate this by a line that's going up over time as they both increase. The adjusted formula or Charles' law formula would just become v1t1 = v2t2. Here we'd say that our initial volume is v1, our initial temperature is t1, final volume is v2, and our final temperature is T2. So remember, when it comes to Charles' Law, we say that volume and temperature are directly proportional, which means they both can increase or decrease together if our moles n and our pressure p are held constant or fixed.

Chemistry Gas Laws Example 1

Here we're told that a 10 liter cylinder with a movable piston contains 10 grams of xenon gas. When an additional 10 grams of xenon gas are added, the volume increases. Which chemistry gas law can be used to justify this result? Alright. So, within this question, what are we talking about? We're discussing the volume of a container, and they tell me when I add grams, it increases. So, they could be asking me to determine what the new volume is, so \( V_2 \). They're giving me 10 grams of gas. If I know the grams of a gas, I can use that to find the moles of the gas. And then, by adding additional grams of the gas, that changes the moles. Right? So, basically, using this information, it could help me find my second set of moles. So this question is really highlighting the fact that it's your volume and your moles that are changing. And based on the chemistry gas law that we know, we know that when we're dealing with volume and moles, it has to be Avogadro's law. So option B would be the correct choice. It is the only chemistry gas law that's talking about changes between volume and moles.

A 10.0 L cylinder with a movable piston exerts 3.00 atm of pressure. What will happen to the pressure if the volume of the container increases to 20.0 L?

• A. It will double
• B. It will decrease by half
• C. It will increase slightly
• D. No change

Answer: (B)

A sealed container with a movable piston contains a gas with a pressure of 1380 torr, a volume of 820 mL and a temperature of 31°C. What would the volume be if the new pressure is now 2.83 atm, while the temperature decreased to 25°C?

• A. 0.0253 L
• B. 0.167 L
• C. 0.326 L
• D. 0.516 L
• E. 1.46 L

Answer: (D)

Here’s what students ask on this topic:

What is Boyle's Law and how is it represented mathematically?

Boyle's Law states that the volume of a gas is inversely proportional to its pressure when the temperature and the number of moles are held constant. Mathematically, it is represented as:

$P{V}_1=P_2{V}_2$

where $P_1$ and $V_1$ are the initial pressure and volume, and $P_2$ and $V_2$ are the final pressure and volume. This inverse relationship means that if the volume increases, the pressure decreases, and vice versa.

How does Gay Lussac's Law describe the relationship between pressure and temperature?

Gay Lussac's Law, also known as Amontons' Law, states that the pressure of a gas is directly proportional to its temperature when the volume and the number of moles are held constant. This means that as the temperature increases, the pressure also increases. Mathematically, it is represented as:

$\frac{P_1}{T_1}=\frac{P_2}{T_2}$

where $P_1$ and $T_1$ are the initial pressure and temperature, and $P_2$ and $T_2$ are the final pressure and temperature. Remember to use Kelvin for temperature in these calculations.

What is Avogadro's Law and how does it relate volume and moles of gas?

Avogadro's Law states that the volume of a gas is directly proportional to the number of moles of the gas when the pressure and temperature are held constant. This means that as the number of moles increases, the volume also increases. Mathematically, it is represented as:

$\frac{V_1}{n_1}=\frac{V_2}{n_2}$

where $V_1$ and $n_1$ are the initial volume and number of moles, and $V_2$ and $n_2$ are the final volume and number of moles. This law helps explain why gases expand when more gas molecules are added to a container.

How does Charles's Law explain the relationship between volume and temperature?

Charles's Law states that the volume of a gas is directly proportional to its temperature when the pressure and the number of moles are held constant. This means that as the temperature increases, the volume also increases. Mathematically, it is represented as:

$\frac{V_1}{T_1}=\frac{V_2}{T_2}$

where $V_1$ and $T_1$ are the initial volume and temperature, and $V_2$ and $T_2$ are the final volume and temperature. Remember to use Kelvin for temperature in these calculations.

What is the Ideal Gas Law and how do the individual gas laws derive from it?

The Ideal Gas Law is a fundamental equation that relates the pressure, volume, temperature, and number of moles of a gas. It is represented as:

$PV=nRT$

where $P$ is the pressure, $V$ is the volume, $n$ is the number of moles, $R$ is the gas constant, and $T$ is the temperature in Kelvin. The individual gas laws (Boyle's, Charles's, Gay Lussac's, and Avogadro's) can be derived from the Ideal Gas Law by holding two of the variables constant and observing the relationship between the other two.