Scientists and Their Discoveries: The Ideal Gas Law Poster Illustrated Teacher's Guide

Transcription

1 Scientists and Their Discoveries: The Ideal Gas Law Poster Illustrated Teacher's Guide # Paper # Laminated Background Gas Law Basics Matter most frequently takes the form of a solid, liquid, or gas. We are all familiar with balloons at birthday parties or at other events. Sometimes we fill balloons with our breath or with helium from a cylinder. How does our breath or added helium fill the balloon? What happens if the balloon is warmed or cooled? What causes a balloon to burst if too much gas is added? Over the years many scientists have contributed to the development of our modern explanation for the behavior of gases. They conducted many experiments and analyzed their data to identify trends and to determine the relationships among pressure, volume, temperature,and number of particles. These results are commonly called the Gas Laws and they are generally named in honor of the scientist who first discovered them. The gas laws allow scientists to predict the behavior of a gas under most conditions. Figure 1. Balloon being inflated with hot air Avogadro s Law Amedeo Avogadro was an Italian scientist and mathematician who lived from 1776 to He measured the mass of the volume of many different gases. He hypothesized that equal volumes of different gases at the same temperature and pressure contain the same number of particles. He then related the relative densities of any two gases to the molecular weights (molar masses) of the gases. This hypothesis is called Avogadro s Law or Avogadro's Principle. Avogadro s insights led to the development of the mole concept in chemistry. Figure 2. Amedeo Avogadro 1

2 Boyle s Law Sir Robert Boyle was an Irish scientist who lived from 1627 to He contributed to our modern understanding of physics and chemistry. Boyle was a founding member of the Royal Society of London, where he and his colleagues laid the foundation for what would become known as the Scientific Method. Boyle worked with gases and used air pumps to create vacuums. He discovered that at constant temperature, the volume of a sample of gas is indirectly (inversely) proportional to its pressure. This relationship is known as Boyle s Law. It is written as P1V1 = P2V2. Figure 3. Sir Robert Boyle Charles Law Jacques Charles was a French chemist and physicist, who lived from 1746 to In 1787, nearly a century after Robert Boyle s work, Jacques Charles studied the behavior of gases under different conditions. He discovered that the volume of a sample of gas at constant pressure was directly proportional to its temperature in the Kelvin scale. This relationship is called Charles Law. It is written as V1/T1 = V2/T2. Figure 4. Jacques Charles Dalton s Law of Partial Pressures John Dalton was a British chemist, physicist, and teacher who lived from1768 to Dalton is one of the fathers of modern atomic theory. He discovered that each gas in a mixture of gases exerts a pressure (called the partial pressure) independent of the other gases. The total pressure of a mixture of gases is equal to the sum of the partial pressure of each gas. The composition of dry air is about 77% nitrogen, 21% oxygen, 1% argon, 0.4% carbon dioxide and traces of other gases. A pressure gauge on an air compressor filled with dry air would indicate the total pressure exerted by each gas in the mixture. This concept is known as Dalton s Law of Partial Pressures or simply as Dalton s Law. It is written as PT = P1 + P2 + P3 +...Pn for n number of gases. Figure 5. John Dalton 2

3 Ideal Gas Law The Ideal Gas Law is mainly derived from Avogadro s, Boyle s, Charles, and Dalton s Laws. The Ideal Gas Law is written as the equation: PV = nrt, where P is the pressure of the gas, V is the volume of the gas, n is the number of moles of particles in the gas sample, T is the Kelvin temperature of the gas and R is the Ideal Gas Constant. A commonly used value for R is L atm / mol K or liter atmospheres per mole Kelvin. Ideal Gas Law PV = nrt Ideal Gas Law Conclusions Four key conclusions can be drawn from the Ideal Gas Law: 1) At constant volume and temperature of a gas, pressure increases as more gas particles are added (and vice versa) as shown in Figure 6. 2) At constant temperature and pressure, the volume increases as more gas particles are added (and vice versa) as shown in Figure 7. 3) For a sample of gas having a constant number of particles and volume, the pressure increases as the temperature increases (and vice versa) as shown in Figure 8. 4) For a sample of gas having a constant number of particles and temperature, the pressure decreases as volume increases (and vice versa) as shown in Figure 9. More gas molecules added Pressure increases Constant Temperature More gas molecules Constant Temperature & Pressure Figure 7. Volume varies with # particles Figure 6. Pressure varies with # particles Temperature increases Pressure increases Volume decreases Figure 8. Pressure directly varies with temperature Pressure increases Figure 9. Pressure varies inversely with volume 3

4 Worksheet # 1 Identifying Gas Laws Label diagrams #1 4 shown below with the name of the gas law illustrated COPYMASTER: Permission granted to make unlimited copies. Copy use confined to educational purposes within a single school building. Copyright Neo/SCI. 4

5 Worksheet # 2 Summarizing Gas Laws 1. Summarize Avogadro s Law and identify the conditions that are held 2. Describe Boyle s Law and express it in the form of an equation. Be certain to specify what conditions are held 3. Describe Charles Law and express it in the form of an equation. Be certain to specify what conditions are held 4. Describe Dalton s Law and express it in the form of an equation. Be certain to specify what conditions are held 5. List the equation for the Ideal Gas Law and describe it in your own words. COPYMASTER: Permission granted to make unlimited copies. Copy use confined to educational purposes within a single school building. Copyright Neo/SCI. 5

6 Worksheet # 1 Identifying Gas Laws (Expected Results) Label diagrams #1 4 shown below with the name of the gas law illustrated. 1. Avogadro s Law 2. Charles Law 3. Boyle s Law 4. Dalton s Law (of Partial Pressures) 6

7 Worksheet # 2 Summarizing Gas Laws (Expected Results) 1. Summarize Avogadro s Law and identify what conditions are held At the same (constant) temperature and pressure conditions, equal volumes of different gases contain the same number of particles. 2. Describe Boyle s Law and express it in the form of an equation. Be certain to specify what conditions are held For a sample of gas at constant temperature (and number of particles), the volume is inversely proportional to its pressure. P 1 V 1 = P 2 V Describe Charles Law and express it in the form of an equation. Be certain to specify what conditions are held For a sample of gas at constant pressure (and number of particles), the volume is directly proportional to its Kelvin temperature. V 1 /T 1 =V 2 /T 2 4. Describe Dalton s Law and express it in the form of an equation. Be certain to specify what conditions are held The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas. The number of particles of each gas in the mixture is PT = P 1 + P 2 + P Pn 5. List the equation for the Ideal Gas Law and describe it in your own words. PV=nRT Answers may vary. The product of the pressure and volume of a sample of gas is equal to the product of the number of moles of gas times the gas constant and the Kelvin temperature of the gas. 7