Gas Laws: Pressure, Volume, and Hot Air

Introduction Welcome! This interactive lesson will introduce three ways of predicting the behavior of gases: Boyle’s Law, Charles’ Law, and the Gay-Lussac Law.

Lesson 1: Basic Terminology This lesson reviews terms used to describe the properties and behavior of gases.

Opening thoughts… Have you ever: Seen a hot air balloon?

Opening thoughts… Have you ever: Seen a hot air balloon? Had a soda bottle spray all over you? Baked (or eaten) a nice, fluffy cake? These are all examples of gases at work!

Properties of Gases You can predict the behavior of gases based on the following properties: Pressure Volume Amount (moles) Temperature Lets review each of these briefly…

You can predict the behavior of gases based on the following properties: Pressure Volume Amount (moles) Temperature

Pressure Pressure is defined as the force the gas exerts on a given area of the container in which it is contained. The SI unit for pressure is the Pascal, Pa. If you’ve ever inflated a tire, you’ve probably made a pressure measurement in pounds (force) per square inch (area).

You can predict the behavior of gases based on the following properties: Pressure Volume Amount (moles) Temperature

Volume Volume is the three-dimensional space inside the container holding the gas. The SI unit for volume is the cubic meter, m3. A more common and convenient unit is the liter, L. Think of a 2-liter bottle of soda to get an idea of how big a liter is. (OK, how big two of them are…)

You can predict the behavior of gases based on the following properties: Pressure Volume Amount (moles) Temperature

Amount (moles) Amount of substance is tricky. The SI unit for amount of substance is the mole, mol. Since we can’t count molecules, we can convert measured mass (in kg) to the number of moles, n, using the molecular or formula weight of the gas. By definition, one mole of a substance contains approximately 6.022 x 1023 particles of the substance. You can understand why we use mass and moles!

You can predict the behavior of gases based on the following properties: Pressure Volume Amount (moles) Temperature

Temperature Temperature is the measurement of heat…or how fast the particles are moving. Gases, at room temperature, have a lower boiling point than things that are liquid or solid at the same temperature. Remember: Not all substance freeze, melt or evaporate at the same temperature. Water will freeze at zero degrees Celsius. However Alcohol will not freeze at this temperature.

Temperature converstions The first step to solving gas law problems should be converting all temperatures to absolute temperatures. This is the most common place mistakes are made in this type of problem. T K = 273 + °C Ti = initial temperature = 27 °C Ti K = 273 + 27 Ti K = 300 K Tf = final temperature = 77 °C Tf K = 273 + 77 Tf K = 350 K

How do they all relate? Some relationships of gases may be easy to predict. Some are more subtle. Now that we understand the factors that affect the behavior of gases, we will study how those factors interact.

Lesson 2: Boyle’s Law This lesson introduces Boyle’s Law, which describes the relationship between pressure and volume of gases. Equation: P₁V₁= P₂V₂ so P₂=(P₁V₁) / V₂ and V₂ = (P₁V₁) / P₂

Boyle’s Law This law is named for Charles Boyle, who studied the relationship between pressure, p, and volume, V, in the mid-1600s. Boyle determined that for the same amount of a gas at constant temperature, results in an inverse relationship: when one goes up, the other comes down. Remember: Boys Play Video games pressure volume

What does Boyle’s Law mean? Suppose you have a cylinder with a piston in the top so you can change the volume. The cylinder has a gauge to measure pressure, is contained so the amount of gas is constant, and can be maintained at a constant temperature. A decrease in volume will result in increased pressure. Hard to picture? Let’s fix that!

Boyle’s Law at Work… Doubling the pressure reduces the volume by half. Conversely, when the volume doubles, the pressure decreases by half.

Lesson 2 Complete! This concludes Lesson 2 on Boyle’s Law! Click the Main Menu button below, then select Lesson 3 to learn about how temperature fits in.

Lesson 3: Charles’ Law This lesson introduces Charles’ Law, which describes the relationship between volume and temperature of gases. Equation: V₁/T₁= V₂/T₂ Or V₂=V₁/T₁ x T₂ and T₂= T₁/V₁ x V₂

Charles’ Law This law is named for Jacques Charles, who studied the relationship volume, V, and temperature, T, around the turn of the 19th century. This defines a direct relationship: With the same amount of gas he found that as the volume increases the temperature also increases. If the temperature decreases than the volume also decreases. Remember: Charlie Brown was a T V Show volume temperature

What does Charles’ Law mean? Suppose you have that same cylinder with a piston in the top allowing volume to change, and a heating/cooling element allowing for changing temperature. The force on the piston head is constant to maintain pressure, and the cylinder is contained so the amount of gas is constant. An increase in temperature results in increased volume. Hard to picture? Let’s fix it (again)! https://www.youtube.com/watch?v=z1hzatoE1tg

Charles’ Law at Work… As the temperature increases, the volume increases. Conversely, when the temperature decreases, volume decreases.

Lesson 3 Complete! This concludes Lesson 3 on Charles’ Law!

Gay-Lussac’s Law This law defines a direct relationship: With the same amount of gas he found that as the pressure increases the temperature also increases. If the temperature decreases than the pressure also decreases. P1/T1 = P2/T2 Remember: Gay – Lussac used T P on his neighbors yard

Mission complete! You have completed the lessons and review. Congratulations! You should now have a better understanding of the properties of gases, how they interrelate, and how to use them to predict gas behavior.