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## Gas Laws

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**Gas Laws**NEXT**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… MAIN MENU PREVIOUS NEXT**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). MAIN MENU PREVIOUS NEXT**Pressure and Elevation**• Air Pressure decreases as elevation increases.**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 (it’s half the size of the bottle). MAIN MENU PREVIOUS NEXT**Amount (moles)**As we’ve already learned, the SI unit for amount of substance is the mole, mol. We can’t count molecules, we can convert measured mass to the number of moles, n, using the molecular or formula weight of the gas. By definition, one mole of a substance contains approximately 6.02 x 1023 particles of the substance. MAIN MENU PREVIOUS NEXT**Temperature**Temperature is the measurement with which you’re probably most familiar (and the most complex to describe completely). We will be using temperature measurements in Kelvin, K, because of the concept of Absolute 0. The Kelvin scale starts at Absolute 0, which is -273.15°C. To convert Celsius to Kelvin, add 273.15. MAIN MENU PREVIOUS NEXT**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. MAIN MENU PREVIOUS NEXT**Lesson 2: Boyle’s Law**This lesson introduces Boyle’s Law, which describes the relationship between pressure and volume of gases. MAIN MENU NEXT**Boyle’s Law**• This law is named for Charles Boyle, who studied the relationship between pressure, p, and volume, V, in the mid-1600s. • He determined that for the same amount of a gas at constant temperature, p x V = constant • This defines an inverse relationship:when one goes up, the othercomes down. pressure volume MAIN MENU PREVIOUS NEXT**What does Boyle’s Law mean?**p x V = constant 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! MAIN MENU PREVIOUS NEXT**Boyle’s Law at Work…**Doubling the pressure reduces the volume by half. Conversely, when the volume doubles, the pressure decreases by half. MAIN MENU PREVIOUS NEXT**Application of Boyle’s Law**• Boyle’s Law can be used to predict the interaction of pressure and volume. • If you know the initial pressure and volume, and have a target value for one of those variables, you can predict what the other will be for the same amount of gas under constant temperature. • Let’s try it! MAIN MENU PREVIOUS NEXT**Application of Boyle’s Law**p1 x V1 = p2 x V2 p1 = initial pressure V1 = initial volume p2 = final pressure V2 = final volume If you know three of the four, you can calculate the fourth. MAIN MENU PREVIOUS NEXT**Application of Boyle’s Law**p1 x V1 = p2 x V2 p1 = 1 KPa V1 = 4 liters p2 = 2 KPa V2 = ? Solving for V2, the final volume equals 2 liters. So, to increase the pressure of 4 liters of gas from 1 KPa to 2 KPa, the volume must be reduced to 2 liters. MAIN MENU PREVIOUS NEXT**Boyle’s Law: Summary**• Pressure x Volume = Constant • p1 x V1 = p2 x V2 • With constant temperature and amount of gas, you can use these relationships to predict changes in pressure and volume. MAIN MENU PREVIOUS NEXT**Lesson 3: Charles’ Law**This lesson introduces Charles’ Law, which describes the relationship between volume and temperature of gases. MAIN MENU NEXT**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. • He determined that for the same amount of a gas at constant pressure, V / T = constant • This defines a direct relationship: an increase in one results in an increase in the other. volume temperature MAIN MENU PREVIOUS NEXT**Charles’ Law at Work…**As the temperature increases, the volume increases. Conversely, when the temperature decreases, volume decreases. MAIN MENU PREVIOUS NEXT**Application of Charles’ Law**• Charles’ Law can be used to predict the interaction of temperature and volume. • If you know the initial temperature and volume, and have a target value for one of those variables, you can predict what the other will be for the same amount of gas under constant pressure. • Let’s try it! MAIN MENU PREVIOUS NEXT**Application of Charles’ Law**V1 / T1 = V2 / T2 V1 = initial volume T1 = initial temperature V2 = final volume T2 = final temperature If you know three of the four, you can calculate the fourth. MAIN MENU PREVIOUS NEXT**Application of Charles’ Law**V1 / T1 = V2 / T2 V1 = 2.5 liters T1 = 250 K V2 = 4.5 liters T2 = ? Solving for T2, the final temperature equals 450 K. So, increasing the volume of a gas at constant pressure from 2.5 to 4.5 liters results in a temperature increase of 200 K. MAIN MENU PREVIOUS NEXT**Charles’ Law: Summary**• Volume / Temperature = Constant • V1 / T1 = V2 / T2 • With constant pressure and amount of gas, you can use these relationships to predict changes in temperature and volume. MAIN MENU PREVIOUS NEXT**Avogadro’s Law**• This law is named for Amedo Avogadro, who studied the relationship moles, n, and volume, V, in the 1800s • He determined that for gas at constant temperature and constant pressure, V / n = constant • This defines a direct relationship: an increase in one results in an increase in the other. volume moles**Application of Avogadro’s Law**V1 / n1 = V2 / n2 V1 = initial volume n1 = initial number of moles V2 = final volume n2 = final number of moles If you know three of the four, you can calculate the fourth.**Application of Avogadro’s Law**V1 / n1 = V2 / n2 V1 = 5.00 L n1 = 0.965 mol V2 = ? n2 = 1.80 mol • Solving for V2 , the final volume equals 9.32 L.**Lesson 4: Ideal Gas Law**This lesson combines all the properties of gases into a single equation. MAIN MENU NEXT**Ideal Gas Law**Combining Boyle’s, Charles’s, Avogadro’s and Gay-Lussac’s laws allows for developing a single equation: P*V = n*R*T P = pressure V = volume n = number of moles R = universal gas constant T = temperature MAIN MENU PREVIOUS NEXT**Ideal Gas Law**P*V = n*R*T By remembering this single equation, you can predict how any two variables will behave when the others are held constant. MAIN MENU PREVIOUS NEXT**Gas Constant**• The Ideal Gas Law includes use of the universal gas constant (R). • The value of the constant depends on the units used to define the other variables, but will always be given to you. MAIN MENU PREVIOUS NEXT**Ideal Gas Law: Summary**• P*V = n*R*T • Learn it! • Use it! • This single equation can be used to predict how any two variables will behave when the others are held constant. MAIN MENU PREVIOUS NEXT**Review**This review contains multiple choice questions on the material covered by Lessons 1 – 4. Select an answer by clicking the corresponding letter. MAIN MENU NEXT**Question 1**Based on Boyle’s Law (p * V = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and temperature (T) are held constant, pressure and volume are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related MAIN MENU**Question 1 is Correct!**Based on Boyle’s Law (p * V = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and temperature (T) are held constant, pressure and volume are: a. Inversely proportional: if one goes up, the other comes down. Decreasing volume increases pressure. Increasing volume decreases pressure. pressure volume MAIN MENU NEXT**Try Question 1 again…**Based on Boyle’s Law (p * V = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and temperature (T) are held constant, pressure and volume are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related You selected b. While pressure and volume are related, it is not a direct proportion. Try again! MAIN MENU TRYAGAIN**Try Question 1 again…**Based on Boyle’s Law (p * V = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and temperature (T) are held constant, pressure and volume are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related You selected c. Pressure and volume are related. Is the relationship inverse or direct? MAIN MENU TRYAGAIN**Question 2**Based on Charles’ Law (V / T = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and pressure (p) are held constant, volume and temperature are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related MAIN MENU**Try Question 2 again…**Based on Charles’ Law (V / T = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and pressure (p) are held constant, volume and temperature are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related You selected a. While volume and temperature are related, it is not an inverse proportion. Try again! MAIN MENU TRYAGAIN**Question 2 is Correct!**Based on Charles’ Law (V / T = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and pressure (p) are held constant, volume and temperature are: b. Directly proportional: if one goes up, the other goes up. volume temperature Increasing temperature increases volume. Decreasing temperature decreases volume. MAIN MENU NEXT**Try Question 2 again…**Based on Boyle’s Law (p * V = constant) or the Ideal Gas Law (p*V=n*R*T), when the number of moles (n) and temperature (T) are held constant, pressure and volume are: a. Inversely proportional: if one goes up, the other comes down. b. Directly proportional: if one goes up, the other goes up. c. Not related You selected c. Pressure and volume are related. Is the relationship inverse or direct? MAIN MENU TRYAGAIN**Question 3**Lets put the Ideal Gas Law (p*V=n*R*T) to some practical use. To inflate a tire of fixed volume, what is the most effective way to increase the pressure in the tire? a. Increase the force pressing on the outside of the tire. b. Increase the temperature of the gas (air) in the tire. c. Increase the amount (number of moles) of gas in the tire. MAIN MENU**Try Question 3 again…**Lets put the Ideal Gas Law (p*V=n*R*T) to some practical use. To inflate a tire of fixed volume, what is the most effective way to increase the pressure in the tire? a. Increase the force pressing on the outside of the tire. b. Increase the temperature of the gas (air) in the tire. c. Increase the amount (number of moles) of gas in the tire. While increasing the load in the car might increase the force on the tires, it would prove to be a difficult way to adjust tire pressure. Try again! MAIN MENU TRYAGAIN**Try Question 3 again…**Lets put the Ideal Gas Law (p*V=n*R*T) to some practical use. To inflate a tire of fixed volume, what is the most effective way to increase the pressure in the tire? a. Increase the force pressing on the outside of the tire. b. Increase the temperature of the gas (air) in the tire. c. Increase the amount (number of moles) of gas in the tire. Increasing the temperature of the air in the tire would definitely increase pressure. That is why manufacturers recommend checking air pressures when the tires are cold (before driving). But how would you increase temperature without damaging the tire? Is there a more practical solution? MAIN MENU TRYAGAIN**Question 3 is Correct!**Lets put the Ideal Gas Law (p*V=n*R*T) to some practical use. To inflate a tire of fixed volume, what is the most effective way to increase the pressure in the tire? a. Increase the force pressing on the outside of the tire. b. Increase the temperature of the gas (air) in the tire. c. Increase the amount (number of moles) of gas in the tire. When you inflate a tire with a pump, you are adding air, or increasing the amount of air in the tire. This will often result in a slight increase in temperature because a tire is not a controlled environment. Such deviations and quirks will be discussed in class! MAIN MENU NEXT**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. • Please click on the button below to reset the lesson for the next student. Thanks! Return to Title Slide