Gas Laws Introduction PDF - Practice Questions & Summary

Name: Introduction to Gas Laws Notes: Additional Notes: To begin, let’s consider what we already know about gases. Gases take the volume and shape of their container....

Name: Introduction to Gas Laws Notes: Additional Notes: To begin, let’s consider what we already know about gases. Gases take the volume and shape of their container. Gases are highly compressible. Gases will mix evenly and completely when confined to the same container. Gases have low densities when compared with liquids and solids. In order to visualize how gases will change under different circumstances, we need to know a little bit about the nature of gases. Kinetic Molecular Theory describes the motion and nature of gas particles and has the following assumptions: The particles in a gas sample are very very small, when compared with the distances between them. This means that their size is negligible and so they can be thought of as point-masses. Gas particles are in constant random motion. They move in straight lines until they collide with one another or the walls of the container. The collisions are perfectly elastic; no energy is lost or gained in the collisions, it is simply transferred. Gas particles neither attract nor repel one another. The average kinetic energy* of the molecules is proportional to the temperature of the particles measured in Kelvin. Gas pressure comes from the collisions of the particles with the walls of the container, more collisions or collisions with more force result in higher pressure. A Chemistry Guide  When discussing gases, there are four key variables to consider, pressure, volume, temperature and number of moles. Pressure P Measures the force per unit 760 torr= 101.3 kPa= 1atm= 760 mmHg area. Volume V Measures the space that 1 L = 1000 ml something occupies Temperature T Measures the average kinetic KELVIN ONLY FOR GASES energy of the particles °C + 273 = K moles n Measures the number of moles particles Pressure was traditionally measured using a barometer or a manometer, now we can use pressure sensors. Pressure of the gas is found by comparing the pressure of the gas with either the pressure of the atmosphere (1 atm - usually) or the pressure of a vacuum (0 atm). A Chemistry Guide  There are several individual gas laws that look at how one variable responds when another one variable is changed. Name Variables Equation Two-Point Relationship Example Equation Boyle’s Law P V 𝑃×𝑉 = 𝑘 P1V1 = P2V2 Inverse Squeezing a sealed water bottle gets harder as the volume decreases. Charles’ Law V T 𝑉 = 𝑘 𝑉1 𝑉2 Direct Taking a balloon 𝑇 = 𝑇1 𝑇2 outside in the cold makes it shrink. Gay-Lussac’s P T 𝑃 = 𝑘 𝑃1 𝑃2 Direct In the winter your 𝑇 = Law 𝑇1 𝑇2 tire pressure decreases. Avogadro’s V n 𝑉 = 𝑘 𝑉1 𝑉2 Direct When you put more 𝑛 = Law 𝑛1 𝑛2 air into a balloon the balloon gets larger. Example Problems: 1) If 2.5 L of a gas at 298 K is heated to 354 K at constant pressure, what is the new volume of the gas? 2) If the pressure of a sample of 1.75 moles of gas is 205 kPa, what will the pressure of the gas be if 2.00 moles are added? 3) If 5.10 liters of gas is at 155 kPa, what will the pressure of the gas be when the volume is decreased to 2.55 liters? A Chemistry Guide  I do: Convert the following pressure values into the other units: atm mmHg torr kPa 1.25 atm 705 torr We do: Read the pressure of the gas for each of the following manometers. We do: What is the pressure of a gas at 325 K, if the pressure of the gas is 805 mmHg at 50.0℃? A Chemistry Guide  You do: 1) Categorize the units with the appropriate variable: moles, Kelvin, kPa, mL, atm, L, mmHg, Celsius, Torr V P n T 2) Convert: a) 785 mmHg ⇒ atm b) 25.70 ℃ ⇒ K c) 892 mL ⇒ L 3) What is the pressure on a gas at 350. K if the pressure is 2.62 atm at 300. K? 4) The volume of a gas at 298K is 0.346 L when the pressure is 201 kPa, what will the volume be when the pressure is 152 kPa at 298K? A Chemistry Guide  5) In a rigid, 6 L container, the pressure of N2 gas is 0.592 atm at 305 K, what temperature will the gas be if the pressure is 0.891 atm? 6) The pressure of a sample of CO2 was 2.00 atm when the temperature was 30.45 ℃, what will the pressure be if the temperature of the sample is heated to 92.01℃? 7) The volume of a balloon was 4.21 L when the temperature was 25.0 ℃, what will the volume of the balloon be when the temperature is 50.0℃? 8) If 15.0 mL of hydrogen gas, H2, is at a pressure of 1.29 atm, what will the volume be when the pressure is 0.658atm? 9) If the pressure of a gas is 513 mmHg when a gas is at 76.3 ℃, what will the pressure be if the temperature is increased by 15.0℃? 10) How many moles are there in a 7.00 L of a gas at a certain temperature and pressure, if 0.369 moles of the same gas at the same conditions occupies 9.75L? A Chemistry Guide