CHEM 1001 Study Guide - Midterm Guide: Ideal Gas Law, Joule, Partial Pressure

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CHEM 1001 Full Course Notes

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Chem 1001 a, t midterm test #1 october 14, 2011. Answer each of the six questions with a few sentences or equations where necessary. (5 marks each) The pressure is low (there is only one mole of gas in 20. 0 l), so attractive forces dominate repulsive forces. Thus the gas with the larger attractive forces will have the lower pressure. Since the ar atoms are larger than the he atoms, the attractive forces in ar are larger than in he, and so the ar has the lower pressure. The concentration of ozone is at a maximum at this altitude. Beginning with nis(s), show the three reactions that lead to acid rain. Nis(s) + 3/2 o2(g) nio(s) + so2(g) E = q + w, so e > 0. Name three ways that hydrogen might be stored in an automobile for use as a fuel. Dissolved in a metal such as pt, pd, .

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The following table presents the solubilities of several gases in water at 25 °C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH₄(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 °C? (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and intermolecular forces. (c) Compare the solubilities of O₂, N₂, and NO, and account for the variations based on molecular structures and intermolecular forces. (d) Account for the much larger values observed for H₂S and SO₂ as compared with the other gases listed. (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C₂H₄ and N₂), and use intermolecular interactions to explain the differences in their solubilities.

The corresponding volume is

b) All three molecules are nonpolar and form very weak interactions with the water molecules. The solubility of ethane is higher that the solubility of methane as ethane is more massive molecule and forms stronger dispersion forces with the water molecule. Ethene is the most soluble gas as the C atoms in ethene are planar, sp² hybridized, and there are π electrons in the orbitals perpendicular to the carbon atoms. π electrons are less tightly held by the nucleus than σ electrons, allowing the dipole of water molecule to disturb the electron density more easily, leading to stronger dipole-induced dipole interactions.

c) The molecular weight is similar for three gases. O₂ and N₂ are nonpolar gases, but more water molecules surround O₂ as it is larger molecule. The O–O bond (double bond) is longer than N–N bond (triple bond). The water attracts nonpolar gases through the weak dipole-induced dipole interactions. NO is the most soluble gas as it has polar bond and the overall molecule is polar as it is linear structure. Water dissolves it via stronger dipole-dipole interactions.

d) H₂S is capable to form weak hydrogen bonds with the water molecules, and these interactions are much stronger than dipole-dipole and dispersion forces. SO₂ is even more soluble in water as it reacts with the water forming H₂SO₃. The very high values for the solubility of gas are the sign that the gas chemically reacts with the solvent.

d) N₂ and CH₄. Solubility of N₂ is lower as N₂ is smaller molecule than CH₄ and less hydrated.

NO and C₂H₆ have similar water solubility. NO is more soluble than ethane and form dipole-dipole interactions, but the dispersion forces of ethane and water are stronger than dispersion forces between NO and water as ethane is larger, more polarizable molecule. The sum of all intermolecular interactions is similar for these two gases, leading to the similar water solubility.

NO and O₂. NO is more soluble as it is polar molecule and form stronger intermolecular forces with polar solvent molecules compared to nonpolar O₂ molecule.

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1. A 334 mL cylinder contains 5.225 g of Helium at 23 Â°C. How many grams of He must be released to reduce the pressure to 75 atm? (Show all work.)

2. Place the following gases in order of increasing average speed at 25 Â°C: Ne, HBr, SO2, NF3, CO, He.

3. Suppose 120.0 kg of N2 is stored in a 1100.0 L metal cylinder at 280 Â°C. Calculate the pressure inside the canister assuming all of the liquid nitrogen vaporizes using both the ideal gas equation and the Van deer Waals equation. If the storage tank is rate to 180 atm, will the canister rupture when solving using the two methods? (Show all work.)

4. Arrange the following intermolecular forces in order of increasing strength. (Hydrogenâ bonding, DipoleâDipole, IonâDipole, London Dispersion Forces, and Ionic Bond)

5. Which of the two molecules, propane (C3H8) or heptane (C7H16), would have a

a. Greater London Dispersion Forces

b. Lower boiling point

c. Greater viscosity

6. Explain why waterâs boiling point is over 100Â°C higher than the heaviest molecule from the same column such as H2S (â60.0Â°C), H2Se (â41.3Â°C), and H2Te (â2.2Â°C) using intermolecular forces.

7. Use the ClausiusâClapeyron equation to determine the enthalpy of vaporization using the data below. An experiment was preformed to determine that a certain liquid has a vapor pressure of 13.95 torr at 25.0Â°C and 144.78 torr at 75.0Â°C. (Hint: Remember to change the temperature to Kelvin.)