CHM 1321 Lecture Notes - Lecture 3: Hydrogen Bond, Intermolecular Force, London Dispersion Force

Learning Goal: To be able to predict and calculate properties of real gases. Kinetic molecular theory makes certain assumptions about gases that are, in fact, not true for real gases. Therefore, the measured properties of a gas are often slightly different from the values predicted by the ideal gas law. The van der Waals equation is a more exact way of calculating properties of real gases. The formula includes two constants, a and 6, that are unique for each gas. The van der Waals equation is (p + an^2/V^2) (V - nb) = nRT, where P is the pressure, n the number of moles of gas, V the volume, T the temperature, and R the gas constant. All real gases possess intermolecular forces that can slightly decrease the observed pressure. In the van der Waals equation, the variable P is adjusted to P + an^2/V^2, where a is the attractive force between molecules. The volume of a gas is defined as the space in which the gas molecules can move. When using the ideal gas law we make the assumption that this space is equal to the volume of the container. However, the gas molecules themselves take up some space in the container. So in the van der Waals equation, the variable V is adjusted to be the volume of the container minus the space taken up by the molecules, V - nb, where b is the volume of a mole of molecules. 14.0 moles of gas are in a 5.00 L tank at 20.7 degree C. Calculate the difference in pressure between methane and an ideal gas under these conditions. The van der Waals constants for methane are a = 2.300 L^2 middot atin/mol^2 and b = 0.0430 L/mol Express your answer with the appropriate units.

At sufficiently high concentrations melamine forms an insoluble complex with cyanuric acid. The precipitate that forms causes a type of stone leading to severe kidney damage. Given the structure of these molecules below provide a possible intermolecular attraction which would lead to the formation of the precipitate. A) Dipole- Dipole attractions B) Dipole induced-dipole attractions C) London dispersion forces D) Hydrogen-bonding E) None of these Determine the heat of vaporization for dichloromethane provided the graph below. A) 4.14 times 10^2 kJ/mol B) 2.89 times 10^3 kJ/mol C) 9.04 times 10^2 kJ/mol D) 31.4 kJ/mol E) None of these

(1.5 pts) Intramolecular forces of attraction are often important in holding large molecules together. For example, some proteins fold into compact shapes, held together by attractive forces between nearby functional groups. A schematic of a folded protein is drawn here, with the protein backbone indicated by a blue-green ribbon, and various appendages drawn dangling from the chain. What types of intramolecular forces occur at each labeled site (A-F)? HB - Hydrogen Bond, LD - London dispersion, DD - Dipole-Dipole, SB = Salt Bride (ionic) 4. hydrogen bond (CH2)4NHs S-S-CH2 E. CH CH3 CHCH2 CH3 helical structure CHg disulfide bond (2 pts) Rank the compounds in each group in order of increasing boiling point. (1 lowest-3 lowest)