Chemistry Test Review for 03/09/18
List the 5 assumptions of Kinetic Molecular Theory
#1 - Gases consist of many, many tiny particles that are far apart relative to their size. #2 -Collisions between gas particles and between particles and container walls are elastic collisions, which means the collisions conserve energy. #3 -Gas particles are in rapid, continuous, random motion. #4 -There are no forces of attraction or repulsion between gas particles. #5 -The average kinetic energy of gas particles depends on the temperature of the gas. KE = ½ mv2 m = mass, v = speed, since mass is constant for a specific gas, KE depends on speed, which is determined by temperature!
. List the 6 characteristics/properities of gases & define each of them
#1 -Expansion - gases do not have definite shape or volume; they fill the container in which they are enclosed. #2 - Fluidity - Gases glide easily past each other because of insignificant attractive forces between gas molecules. Liquids are also categorized as a fluid. #3 -Low Density - Density of gas is 1/1000 the density of the same substance as liquid or gas. #4 -Compressibility - Volume for a given gas can be greatly decreased. #5 -Diffusion - Spontaneous mixing of the particles of two substances caused by their random motion #6 -Effusion - The process by which gas particles pass through a tiny opening
Problem # 5
. A container of gas begins with a volume of 2.0 L, a pressure of 0.85 atm, and a temperature of 219 K; the volume is decreased to 1.5 liters and the temperature is increased to 250 K. a. The pressure will increase / decrease (circle one). DECREASE b. Using the correct gas law formula, calculate the final pressure of the container. V1 = 2.0 L 1V1 = P2V2 P1 = 0.85 atm T1 T2 T1 = 219 K V2 = 1.5 L (0.85 atm)(2.0 L) = (1.5 L)(x) T2 = 250 K 219 K 250 K P2 = ? P2 = 1.3 atm
Gas Law Statements
. As temperature increases... volume INCREASES (Charles Law). As volume increases... pressure DECREASES (Boyle's Law). As temperature increases... pressure INCREASES (Gay-Lussac's Law).
Problem # 8
Given: PV = nRT P = 1 atm V = nRT/ P n = 2.50 moles V = (2.50 mol)( 0.0821 liter·atm/mol·K)(273 K) R = 0.0821 liter·atm/mol·K 1 atm T = 273K V = ? V = 56.0 L
Problem # 9
How many moles of an unknown gas are there in a 15.0 L container at 25 °C and 2.33 atm of pressure? Given: PV = nRT P = 2.33 atm n = PV/ RT n = ?? moles n = ______(2.33 atml)(15.0 L)_______ R = 0.0821 liter·atm/mol·K (0.0821 liter·atm/mol·K)(298 K) T = 25 °C + 273K = 298 K V = 15.0 L n = 1.43 mol
Problem # 6
The temperature of helium gas in a balloon is increased from 35°C to 45°C. If the balloon begins with a volume of 2.0 L, what is the final volume? a. The volume will increase / decrease (circle one). INCREASE b. Using Charles' Law, calculate the final volume. Given: V1 = V2 2.0 L = V2__ V1 = 2.0 L T1 T2 308 K 318 K T1 = 35 °C + 273 K = 308 K V2 = ? (308 K)V2 =(2.0 L) (318 K) T2 = 45 °C + 273 K = 318 K (308 K)V2 = 636 L-K V2 = 2.06 L
What is Kinetic Molecular Theory?
Explains how IDEAL gases behave. It is empirically supported. It defines 5 assumptions about the behavior of ideal gases.
What does STP stand for and what are the values associated with STP?
Standard Temperature and Pressure. T = 0oC (or 273 K) and P = 1 atm or 101.3 kPa or 760 mmHg
Problem # 7
You are about to go scuba diving and your tank is filled with 3 gases. The partial pressure of O2 is 0.38 atm, for N2 it's 0.72 atm, and for CO2 it is 0.05 atm. What is the total pressure in the tank? PTotal = P1 + P2 + P3 PTotal = 0.38 atm 0+ 0.72 atm + 0.05 atm = 1.15 atm
Explain how each of these 3 relationships exist: (How does it work? What's happening? What's a real world example?)
Temperature and volume: As temperature increases, particles are moving faster. If pressure remains constant, this means that the volume would have to increase. Real world example: A torch is used to heat the air molecules inside the balloon. The molecules move faster and disperse within the space. The gas inside the balloon takes up more space, becoming less dense than the air surrounding it. As such, the hot air inside the balloon rises because of its decreased density and causes the balloon to float. Volume and pressure: Pressure is measured by collisions of particles. If the volume is increased, this means the same amount of particles have more space to move around in, which means less collisions against the sides of the container, meaning less pressure. Real world example: Syringes of all types utilize Boyle's law on a very basic level. When you pull the plunger out on a syringe, it causes the volume within the chamber to increase. As we know, this causes the pressure to do the opposite, which then creates a vacuum attempting to re-pressurize back to atmospheric levels. Since the only fluid available on the other side of the needle tends to be a liquid such as blood, which gets sucked into the chamber. This then reduces the volume and increases the pressure back to where it wants to be. Temperature and pressure: If temperature is increased, the particles have more kinetic energy, meaning greater velocity, meaning more collisions meaning greater pressure (as long as volume remains constant.) Real world example: The pressure cooker is heated up and sealed tightly so the pressure don't lost to surrounding. The pressure inside the cooker will increase the cooker temperature much higher and cook the food much faster.
