Gases 8.1 - 8.4

what are the assumptions made for The Kinetic Molecular Theory of Gases?

1. Gas particles have negligible volume 2. Gas particles so not have intermolecular attractions or repulsions 3. Gas particles undergo random collisions with each other and the walls of the container 4. Collisions between gas particles (and with the walls of the container) are elastic 5. The average kinetic energy of the gas particles its directly proportional to temperature

If 4 x 10^-4 moles of gas are dissolved in 2 L of solution under an ambient pressure of 2 atm, what will be the molar concentration of the gas under 10 atm?

10^3 M

By what percentage does the real pressure of 1 mole of ammonia in a 1 liter flask at 0 C deviate from its ideal pressure? (Note: R = 0.0821 L*atm / mol*K ; NH3 a = 4.2, b = 0.037)

15 %

What would be the volume of a 1 L sample of helium if its pressure is changed from 12 atm to 4 atm under isothermal conditions?

3L

If the temperature of 2 L of has at constant pressure is changed from 283K to 566K, what would be its final volume?

4 L

If the pressure of a sample of gas with a temperature of 273C is changed from 2atm to 5atm during cooling, what would be the final temperature?

682.5 K

A container with 4 moles of a gas at a pressure of 6 atm has a volume of 12 liters. What is the temperature? (Note: R = 8.21 x 10^-2 L*atm/ mol*K)?

8.2

Which of the following sets of conditions would be LEAST likely to result in ideal gas behavior? A. Higher pressure and low temperature B. Low temperature and larger volume C. Higher pressure and larger volume D> Low pressure and higher temperature

A. Gases deviate from ideal behavior at higher pressures and lower volumes and temperatures, all of which force molecules closer together. The closer they are, the more they can participate in intermolecular forces, which violates the definition of an ideal gas. At extremely high pressures, low volumes, and low temperatures, the size of the gas particles becomes significant, which also violates the definition of an ideal gas.

The kinetic molecular energy states that: A. the average kinetic energy of a molecule of gas is directly proportional to the temperature of the gas in kelvins. B. collisions between gas molecules are inelastic C. gas particles occupy discrete areas of space D. all gas molecules have the same kinetic energy at the same temperature

A. The average kinetic energy is directly proportional to the temperature of a gas in kelvins. The kinetic molecular theory states that collisions between molecules are elastic and thus do not result in loss of energy, eliminating choice B. Gas particles are assumed to take up negligible space in kinetic molecular theory, eliminating choice C. While the average kinetic energy of any gas as a whole is the same at a given temperature, the particles themselves have a distribution of speeds (as seen in the Maxwell-Boltzmann distribution curve), eliminating choice D.

If the attractive forces between gas molecules were to increase while the actual volumes of the molecules remained negligible, what would occur?

According to the can der waals equation, if a is increased wile b remains negligible, the correction term (n^2 a/ V^2) get larger, and the pressure or volume must drop to compensate.

A balloon at standard temperature an pressure contains 0.20 moles of oxygen and 0.60 moles of nitrogen. What is the partial pressure of oxygen in the balloon? A. 0.20 atm B. 0.25 atm C. 0.33 atm D. 0.80 atm

B. At STP, the pressure inside the ballon equals 1 atm. The total number of moles int he balloon equals 0.20 moles plus 0.60 moles, or 0.80 moles. P02 equals the mole fraction of oxygen (0.20/0.80) times the total pressure, 1 atm. The partial pressure of oxygen is therefore 0.25 atm.

The gaseous state of matter is characterized by which of the following properties? I. Gases are compressible II. Gas assume the volume of their containers III. Gas particles exist as diatomic molecules A. I only B. I and II only C. II and III only D. I, II, and III

B. Gases are easily compressible because they travel freely with large amounts of free space between molecules. Because gas particles are far apart from each other and in rapid motion, they tend to take up the volume of the container. Many gases exist as diatomic molecules, but this is not a property that characterizes all gases, eliminating option III.

Ideal gases: I. have no volume II. have particles with no attractive forces between them III. have no mass A. I only B. II only C. I and II only D. I, II, and III

B. Ideal gases are said to have no attractive forces between molecules. While each particle within the gas is considered to have negligible volume, ideal gases as a whole certainly do have a measurable volume, thus option I is eliminated. Gases have molar masses, thus option III is eliminated.

A gaseous mixture contains nitrogen and helium and has a total pressure of 150 torr. The nitrogen particle comprise 80 percent of the gas, and the helium particles take up another 20 percent of the gas. What is the pressure exerted by each individual gas? A. 100 torr nitrogen, 50.0 torr helium B. 120 torr nitrogen, 30.0 torr helium C. 30.0 torr nitrogen, 120 torr helium D. 50.0 torr nitrogen, 100 torr helium

B. The partial pressure of each gas is found by multiplying the total pressure by the mole fraction of the gas. Because 80 percent of the moles are nitrogen, the mole fraction of nitrogen is equal to 0.80. Similarly, for helium, the mole fraction is 0.20. To find the pressure exerted by nitrogen, multiply the total pressure (150 torr) by 0.80 to obtain 120 torr of nitrogen. The remainder, 30 torr, is attributable to helium.

A 0.040 g of magnesium is placed in a beaker of hydrochloric acid. Hydrogen gas is generated according to the following equation: Mg(s) + 2 HCL(aq) --> MgCl2(aq) + H2(g) The gas is collected over water at 25 C, and the gauge pressure during the experiment reads 784 mmHg. The gas displaces a volume of 100mL. The vapor pressure of water at 25 C is approximately 24.0 mmHg. Based on this data, how many moles of hydrogen are produced in this reaction? (Note: R = 0.0821 L*atm / mol*K = 8.314 J/ K*mol) A. 4.04 x 10^-5 moles of Hydrogen B. 4.09 x 10^ -3 moles of Hydrogen C. 3.07 x 10^-2 moles of Hydrogen D. 3.11 moles of hydrogen

B. The pressure of the gas is calculated by subtracting the vapor pressure of the water fro the measured pressure during the experiment: 784mmHg - 24 mmHg = 760 mmHg, or 1 atm. This is because the reaction is carried out in an aqueous environment; the water present will contribute to the partial pressure of the gas over the liquid. The ideal gas law can be used to calculate the moles of hydrogen gas. The volume of the gas is 0.100L, the temperature is 298K.

A gas at temperature of 27 C has a volume of of 60.0 mL. What temperature change is needed to increase this gas to a volume of 90.0mL? A. A reduction of 150 C B. An increase of 150 C C. A reduction of 13.5 C D. An increase of 13.5 C

B. We will use Charles's Law. First, we must convert the temperature to kelvins by adding 273 to get 300K as the initial temperature. Think of this as a proportionality: if the volume is multiplied by 3/2, the temperature will also have to be multiplied by 3/2. Thus the final temperature is 450K , which represents a 150K increase.

What is Boyle's Law equation?

Boyles law shows that it is simply the ideal gas law in which n and T are held constant. NOTE: pressure and volume are inversely related; when one increases the other decreases

In which of the following situations is it impossible to predict how the pressure will change for a gas sample? A. The gas is cooled at a constant volume B. The gas is heated at a constant volume C. The gas is heated, and the volume is simultaneously increased D. The gas is cooled, and the volume is simultaneously increased

C. Both a change in temperature and a change in volume can affect a gas's pressure. So if one of the two variables is kept constant, as in Choices A and B, we'll definitely be able to predict which way will the pressure will change. At a constant volume, heating the gas will increase its pressure, and cooling the gas will decrease it. What about both temperature and volume are changing? If both changes have the same effect on pressure, then we can still predict which way it will change. This is because in Choice D. Cooling the gas and increasing its volume both decrease pressure. Choice C, on the other hand, presents too vague a scenario for us to predict definitely the change in pressure. heating the gas would amplify the pressure, while increasing the volume would decrease it. Without knowing the magnitude of each influence, it's possible to say whether the pressure would increase, decrease, or stay the same.

Experimenters notice that the molar concentration of dissolved oxygen in an enclosed water tank has decreased to one-half its original volume. In an attempt to counter this decrease, they quadrupled the partial pressure of oxygen in the container. What is the final concentration of the gas? A. Half of the original concentration B. The same as the original concentration C. Double the original concentration D. Quadruple the original concentration

C. Initially the concentration of the gas is decreased to one-half its original value. Recall that concentration (solubility) and partial pressure are directly related - as one increases, the other increases. If the experimenters then quadruple the partial pressure of oxygen in the vessel, the solubility is also increased by a factor of four. One-half times four gives twice the original concentration value. Misreading the answer choices as being related to the concentration before the experimenters increased the partial pressure leads to Choice D>.

Given that the gases at the center of the sun have an average molar mass of 2.00 g/mol, compressed to a density of 1.20 g/cm^3 under 1.30 x 10^9 atm of pressure, what is the temperature at the center of the sun? A. 2.6 x 10^4 K B. 2.6 x 10^6 K C. 2.6 x 10^7 K D. 2.6 x 10^10 K

C. The ideal gas law can be modified to include density (rho) because the number of moles of gas, n, is equal tot eh mass divided by the molar mass. Thus, PV = nRT ---> m/M RT --> P m.V x RT/M = (rho)RT/M. Isolating for temperature, we get: T = PM/(rho)R

What is the density of neon gas in g/L at STP? A. 452.3 B. 226.0 C. 1.802 D. 0.9018

D. Density equals mass divided by volume. The mass of 1 mole of neon gas equals 20.2 grams. At STP, 1 mole of neon occupies 22.4L. Dividing the mass, 20.2 grams, by the volume, 22.4L gives an approximate density of 0.902 g/L.

A 8.00 g sample of NH4NO4 (S) is placed into am evacuated 10L flask and heated to 227 C. After the NH4NO3 completely decomposes, what is the approximate pressure in the flask? NH4NO3(s) --> N2O(g) + H2O(g) A. 0.410 atm B. 0.600 atm C. 0.821 atm D. 1.23 atm

D. The first thing to do is balance the given chemical equation: NH4NO3(s) --> N20(g) + 2H2O(g). The mass given is 8.00g, which represents 0.1 mol NH4NO3 (molar mass = 80.0 g/mol). When 0.1 mol of the solid decomposes, it will form 0.1 mol N2O and 0.2 mol water. This gives approximately 0.3 moles of gas product. The ideal gas equation can be used to obtain the pressure in the flask. Choice C is the result if one assumes the equation is balanced, obtaining 0.2 mol gas as the product.

A leak of helium through a small hole occurs at a rate of 3.22 x 10^-5 mol/s. How will the leakage rates of neon and oxygen gases compare to helium at the same temperature and pressure? A. Neon will leak faster than helium; oxygen will leak faster than helium. B. Neon will leak faster than helium, oxygen will leak slower than helium. C. Neon will leak slower than helium; oxygen will leak faster than helium D. Neon will leak slower than helium; Oxygen will leak slower than helium

D. Graham's law of effusion states that the relative rates of diffusion of two gases at the same temperature and pressure are given by the inverse ratio of the square roots of the masses of the gas particles. In other words, a gas with a higher molar mass will leak slowly than a gas with lower molar mass. Both neon and oxygen gases will leak at slower rates than helium because they have more mass than helium.

What is Grams Law?

Describes the behavior of gas diffusion or effusion, stating that gases with lower molar masses will diffuse or effuse faster than gases with higher molar masses at the same temperature. Diffusion or Effusion will be slower for larger molecules.

Describe Diffusion is relation to gases?

Diffusion is the spreading out of particles from high to low concentrations

Describe Effusion in terms of gases?

Effusion is the movement of gas from on e compartment to another through a small opening under pressure

What is Gay-Lussac's Law?

Examination of the equation shows that it is another special case of the ideal gas law in which n and V are held constant. NOTE: An increase in in temperature will increase the pressure in direct proportion

What is Boyles Law?

For a given gaseous sample held at a constant pressure (isothermal conditions), the given volume of the gas is inversely proportional to its pressure.

How can the concentration of carbon dioxide in sodas or other carbonated beverages be so much higher than that of atmospheric carbon dioxide?

High pressures of carbon dioxide gas are forced on top of the liquid in sodas, increasing its concentration in the liquid.

What would happen to the vander waal equation if a and b are both zero?

If a and b are both zero, the vander waals equation of state reduces to the ideal gas law PV = NRT

Give an example of effusion in medicine?

In the clinics, a pleural effusion is a condition in which fluid enters the interpleural space through small opening in the capillaries or lymphatic vessels. This causes a pressure build up around the lungs that hinders breathing.

If the attractive force between gas molecules were to increase while the attractive forces between the molecules remained negligible, what would occur?

Increasing the volume of gas molecules while keeping attraction negligible makes the term V - nb smaller; thus, the pressure or volume must rise to compensate

using Henrys law describe alveolar capillary exchange:

It is seen as a movement of higher to lower concentration of oxygen.

What is Avogadros principle equation?

K = is constant n1 and n2 = are the number of moles of gas 1 and 2 V1 and V2= are the volumes of the gases NOTE: as the number of moles of gas increases the volume increases in direct proportion.

What is Henry's Law?

Law states that the amount of gas dissolved in solution is directly proportional to the partial pressure of that gas at the surface of a solution.

what are the four variables that define a gaseous sample?

P = pressure V = Volume T = temperature n = moles

In what ways do real gases differ from ideal gases?

Real gas molecules have nonnnegligible and attractive forces. Real gases deviate from ideal gases at high pressure (low volume) and low temperature.

what is the difference between STP and Standard state conditions?

STP (273 K and 1 atm) this numbers are mostly used for gas calculations Standard state conditions (298 K, 1 atm, 1 M) are usually used when measuring standard enthalpy, entropy, free energy changes, and electrochemical cell voltage.

How would the kinetic energy of molecules of a gas move as the temperature increases?

The higher the temperature, the faster the molecules move. The larger the molecules, the slower they move.

What is Charles Law?

The law states that at a constant pressure, the volume of the gas is proportional to its absolute temperature, expressed in Kelvin. NOTE: Charles law shows another special case of the ideal gas law which n and P are held constant. Charles law shows a direct relationship between volume and pressure, as one increases the other will also increase in direct proportion.

Hydrogen sulfide (H2S) has a very strong rotten egg odor. Methyl salicylate (C8H8O) has a winter odor, and benzaldehyde (C7H6O) has a pleasant almond odor. If the vapor for these three substances were released at the same time across a room, in which order would one smell the odors? Explain your answer.

The rotten egg odor (hydrogen sulfide) first, almond (benzaldehyde) next, and wintergreen (Methyl salicylate) last. Because all of the gases have the same temperature, they have the same kinetic energy; thus, the lightest molecules travel the fastest.

What is Dalton's Law of Partial Pressures?

Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture. Pt is the total pressure Pa, Pb, Pc are the partial pressure of the gases. The partial pressure if related to its mole fraction and can be determined using the last equation. Xa = moles of gas A / total moles of gas

What is Henry's Law equation?

[A] = the concentration of A in solution kH = Henrys constant Pa = partial pressure of A Henry's constant depends on the the identity of the gas According to this relationship, solubility (concentration) and pressure are directly related. In biology this is important; if the atmospheric pressure changes as it does at high altitude (pressure increases), the amount of gas dissolved in the blood is also elevated.

What is the equation for Vandel waals equation state?

a term corrects for the attractive forces between molecules and as such, will be smaller for gases that are small and less polarizable (Such as helium), and would be larger for gases that are larger and more polarizable. And it will be larger for polar molecules such as HCL and NH3. b term corrects for the volume of of the molecules themselves. larger molecules thus have larger values of b. a is the van der waals term for the attractive forces b if the van der waals term for big particles

What is the average speed of xenon difluoride molecules at 20 C?

about 200 m/s

What is the assumed volume of a gas at STP?

an ideal gas at STP occupied a volume of 22.4L

what is the equation for the Ideal gas law?

keep an eye out for units when given R: R can be in either 8.21 x 10^-2 L*atm/mol*k or R can be given in 8.314 J/K*mol