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chemistry
physical chemistry
Questions and Answers of
Physical Chemistry
Which type of intermolecular attractive force operates between (a) All molecules, (b) Polar molecules, (c) The hydrogen atom of a polar bond and a nearby small electronegative atom?
Based on what you have learned about intermolecular forces, would you say that matter is fundamentally attracted or repulsed by other matter?
Describe the intermolecular forces that must be overcome to convert these substances from a liquid to a gas: (a) SO2, (b) CH3COOH, (c) H2S?
Which type of intermolecular force accounts for each of these differences:(a) CH3OH boils at 65 oC; CH3SH boils at 6 oC.(b) Xe is liquid at atmospheric pressure and 120 K, whereas Ar is a gas under
(a) What is meant by the term polarizability? (b)Which of the following atoms would you expect to be most polarizable: N, P, As, Sb? Explain. (c) Put the following molecules in order of increasing
(a) Which kind of intermolecular attractive force is shown in each case here?(b) Predict which of the four interactions is the weakest?
True or false: (a) For molecules with similar molecular weights, the dispersion forces become stronger as the molecules become more polarizable. (b) For the noble gases the dispersion forces decrease
Which member in each pair has the larger dispersion forces: (a) H2O or H2S, (b) CO2 or CO, (c) SiH4 or GeH4?
Which member in each pair has the stronger intermolecular dispersion forces: (a) Br2 or O2, (b) CH3CH2CH2CH2SH or CH3CH2CH2CH2CH2SH, (c) CH3CH2CH2Cl or (CH3)2CHCl?
Butane and 2-methylpropane, whose space-filling models are shown at the top of the next column, are both nonpolar and have the same molecular formula, C4H10, yet butane has the higher boiling point
Propyl alcohol (CH3CH2CH2OH) and isopropyl alcohol [(CH3)2CHOH], whose space-filling models are shown, have boiling points of 97.2 oC and 82.5 oC, respectively. Explain why the boiling point of
(a) What atoms must a molecule contain to participate in hydrogen bonding with other molecules of the same kind? (b) Which of the following molecules can form hydrogen bonds with other molecules of
Rationalize the difference in boiling points in each pair: (a) HF (20 oC) and HCl (- 85 oC), (b) CHCl3 (61 oC) and CHBr3 (150 oC), (c) Br2 (59 oC) and ICI (97 oC)?
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198oC. By comparison, ethyl alcohol (CH3CH2OH) boils at 78oC at atmospheric pressure. Ethylene glycol
Identify the type or types of intermolecular forces present in each substance and then select the substance in each pair that has the higher boiling point: (a) Propane C3H8 or n-butane C4H10, (b)
Look up and compare the normal boiling points and normal melting points of H2O and H2S.(a) Based on these physical properties, which substance has stronger intermolecular forces? What kind of
Do you expect the viscosity of glycerol, C3H5(OH)3, to be larger or smaller than that of 1-propanol, C3H7OH? Explain?
The following quote about ammonia (NH3) is from a textbook of inorganic chemistry: "It is estimated that 26% of the hydrogen bonding in NH3 breaks down on melting, 7% on warming from the melting to
A number of salts containing the tetrahedral polyatomic anion, BF4- , are ionic liquids, whereas salts containing the somewhat larger tetrahedral ion SO42- do not form ionic liquids? Explain this
The generic structural formula for a 1-alkyl-3-methylimidazolium cation isWhere R is a ¬CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between the 1-alkyl-3-methylimidazolium
(a) Explain why surface tension and viscosity decrease with increasing temperature. (b) Why do substances with high surface tensions also tend to have high viscosities?
(a) Distinguish between adhesive forces and cohesive forces. (b) What adhesive and cohesive forces are involved when a paper towel absorbs water? (c) Explain the cause for the U-shaped meniscus
Explain the following observations: (a) The surface tension of CHBr3 is greater than that of CHCl3. (b) As temperature increases, oil flows faster through a narrow tube. (c) Raindrops that collect
Hydrazine (H2NNH2), hydrogen peroxide (HOOH), and water (H2O) all have exceptionally high surface tensions compared with other substances of comparable molecular weights. (a) Draw the Lewis
The boiling points, surface tensions, and viscosities of water and several alchohols are as follows:(a) For ethanol, propanol, and n-butanol the boiling points, surface tensions, and viscosities all
(a) Would you expect the viscosity of n-pentane, CH3CH2CH2CH2CH3, to be larger or smaller than the viscosity of n-hexane (3.26 × 10-4kg/m-s)(from Table 11.4)? (b) If you compared their viscosities
Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) When ice is heated, it turns to water. (b) Wet clothes dry on a warm summer
If 42.0 kJ of heat is added to a 32.0-g sample of liquid methane under 1 atm of pressure at a temperature of - 170 oC, what are the final state and temperature of the methane once the system
Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) Bromine vapor turns to bromine liquid as it is cooled. (b) Crystals of iodine
Explain why any substance's heat of fusion is generally lower than its heat of vaporization?
Ethyl chloride (C2H5Cl) boils at 12 oC. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25 oC) surface in air, the surface is cooled considerably. (a) What does this observation
For many years drinking water has been cooled in hot climates by evaporating it from the surfaces of canvas bags or porous clay pots. How many grams of water can be cooled from 35 oC to 20 oC by the
Compounds like CCl2F2 are known as chlorofluorocarbons, or CFCs. These compounds were once widely used as refrigerants but are now being replaced by compounds that are believed to be less harmful to
Ethanol (C2H5OH) melts a - 144 oC and boils at 78 °C. The enthalpy of fusion of ethanol is 5.02 kj/mol, and its enthalpy of vaporization is 38.56 kj/mol. The specific heats of solid and liquid
The fluorocarbon compound C2Cl3F3 has a normal boiling point of 47.6 oC. The specific heats of C2Cl3F3(l) and C2Cl3F3(g) are 0.91 j/g - K and 0.67 j/g - K, respectively. The heat of vaporization for
(a) What is the significance of the critical pressure of a substance? (b) What happens to the critical temperature of a series of compounds as the force of attraction between molecules increases? (c)
The critical temperature (K) and pressure (atm) of a series of halogenated are as follows:(a) List the intermolecular forces that occur for each compound.(b) Predict the order of increasing
Explain how each of the following affects the vapor pressure of a liquid: (a) Volume of the liquid, (b) Surface area, (c) Intermolecular attractive forces, (d) Temperature, (e) Density of the
Using this graph of CS2 data,determine (a) the approximate vapor pressure of CS2 at 30 °C, (b) the temperature at which the vapor pressure equals 300 torr, (c) the normal boiling point of CS2?
Acetone, H3CCOCH3, has a boiling point of 56 °C. Based on the data given in Figure 11.25, would you expect acetone to have a higher or lower vapor pressure than ethanol at 25 °C?
(a) Place the following substances in order of increasing volatility: CH4, CBr4, CH2Cl2, CH3Cl, CHBr3, and CH2Br2. Explain. (b) How do the boiling points vary through this series?
True or false: (a) CBr4 is more volatile than CCl4. (b) CBr4 has a higher boiling point than CCl4. (c) CBr4 has weaker intermolecular forces than CCl4. (d) CBr4 has a higher vapor pressure at the
(a) Two pans of water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two
Explain the following observations: (a) Water evaporates more quickly on a hot, dry day than on a hot, humid day. (b) It takes longer to cook an egg in boiling water at high altitudes than it does
Using the vapor-pressure curves in Figure 11.25, (a) Estimate the boiling point of ethanol at an external pressure of 200 torr; (b) Estimate the external pressure at which ethanol will boil at 60
Appendix B lists the vapor pressure of water at various external pressures. (a) Plot the data in Appendix B, vapor pressure (torr) versus temperature (oC). From your plot, estimate the vapor pressure
(a) What is the significance of the critical point in a phase diagram? (b) Why does the line that separates the gas and liquid phases end at the critical point?
(a) What is the significance of the triple point in a phase diagram? (b) Could you measure the triple point of water by measuring the temperature in a vessel in which water vapor, liquid water, and
Referring to Figure 11.28, describe all the phase changes that would occur in each of the following cases: (a) Water vapor originally at 0.005 atm and - 0.5 oC is slowly compressed at constant
The moleculesHave the same molecular formula (C3H8O) but different normal boiling points, as shown. Rationalize the difference in boiling points?
Referring to Figure 11.29, describe the phase changes (and the temperatures at which they occur) when CO2 is heated from - 80 oC to - 20 oC at (a) A constant pressure of 3 atm, (b) A constant
The phase diagram for neon isTemperature (K) Use the phase diagram to answer the following questions. (a) What is the approximate value of the normal melting point? (b) Over what pressure range will
Use the phase diagram of neon to answer the following questions. (a)What is the approximate value of the normal boiling point? (b) What can you say about the strength of the intermolecular forces in
The fact that water on Earth can readily be found in all three states (solid, liquid, and gas) is in part a consequence of the fact that the triple point of water (T = 0.01 °C, P = 0.006 atm) falls
At 25 °C gallium is a solid with a density of 5.19 g/cm3. Its melting point, 29.8 °C, is low enough that you can melt it by holding it in your hand. The density of liquid gallium just above
In terms of the arrangement and freedom of motion of the molecules, how are the nematic liquid crystalline phase and an ordinary liquid phase similar? How are they different?
What observations made by Reinitzer on cholesteryl benzoate suggested that this substance possesses a liquid crystalline phase?
One of the more effective liquid crystalline substances employed in LCDs is the molecule(a) How many double bonds are there in this molecule? (b) Describe the features of the molecule that make it
For a given substance, the liquid crystalline phase tends to be more viscous than the liquid phase. Why?
The phase diagram of a hypothetical substance is(a) Estimate the normal boiling point and freezing point of the substance. (b) What is the physical state of the substance under the following
Describe how a cholesteric liquid crystal phase differs from a nematic phase?
It often happens that a substance possessing a smectic liquid crystalline phase just above the melting point passes into a nematic liquid crystalline phase at a higher temperature. Account for this
The smectic liquid crystalline phase can be said to be more highly ordered than the nematic phase. In what sense is this true?
As the intermolecular attractive forces between molecules increase in magnitude, do you expect each of the following to increase or decrease in magnitude? (a) Vapor pressure, (b) Heat of
Suppose you have two colorless molecular liquids, one boiling at - 84 oC, the other at 34 °C, and both at atmospheric pressure. Which of the following statements is correct? For each statement that
Two isomers of the planar compound 1,2-dichloroethylene are shown here(a) Which of the two isomers will have the stronger dipole - dipole forces? (b) One isomer has a boiling point of 60.3 °C and
In dichloromethane, CH2Cl2, (µ = 1.60 D) the dispersion force contribution to the intermolecular attractive forces is about five times larger than the dipole-dipole contribution. Compared to CH2Cl2,
When an atom or group of atoms is substituted for an H atom I benzene (C6H6), the boiling point changes. Explain the order of the following boiling points: C6H6 (80 oC), C6H5CI (132 oC), C6H5Br (156
The DNA double helix (Figure 24.30) at the atomic level looks like a twisted ladder, where the "rungs" of the ladder consist of molecules that are hydrogen-bonded together. Sugar and phosphate groups
At three different temperatures T1, T2 and T3, the molecules in a liquid crystal align in these ways:(a) At which temperature or temperatures is the substance in a liquid crystalline state? at those
Use the normal boiling points Propane, C3H8, - 42.1 oC Butane, C4H10, - 0.5 oC Pentane, C5H12, 36.1 oC Hexane, C6H14, 68.7 oC Heptane, C7H16, 98.4 oC To estimate the normal boiling point of octane,
One of the attractive features of ionic liquids is their low vapor pressure, which in turn tends to make them nonflammable. Why do you think ionic liquids have lower vapor pressures than most
(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to
The following table gives the vapor pressure of hexafluorobenzene (C6F6) as a function of temperature:(a) By plotting these data in a suitable fashion, determine whether the Clausius-Clapeyron
Suppose the vapor pressure of a substance is measured at two different temperatures.(a) By using the Clausius-Clapeyron equation (Equation 11.1) derive the following relationship between the vapor
The following data present the temperatures at which certain vapor pressures are achieved for dichloromethane (CH2Cl2) and methyl iodide (CH3I):(a)Which of the two substances is expected to have the
A watch with a liquid crystal display (LCD) does not function properly when it is exposed to low temperatures during a trip to Antarctica. Explain why the LCD might not function well at low
(a) At the molecular level, what factor is responsible for the steady increase in viscosity with increasing molecular weight in the hydrocarbon series shown in Table 11.4? (b) Although the viscosity
Acetone, (CH3)2CO, is widely used as an industrial solvent. (a) Draw the Lewis structure for the acetone molecule and predict the geometry around each carbon atom. (b) Is the acetone molecule polar
List the three states of matter in order of] (a) Increasing molecular disorder and (b) Increasing intermolecular attractions. (c) Which state of matter is most easily compressed?
The table shown here lists the molar heats of vaporization for several organic compounds. Use specific examples from this list to illustrate how the heat of vaporization varies with(a) Molar mass,(b)
Liquid butane, C4H10, is stored in cylinders to be used as a fuel. The normal boiling point of butane is listed as - 0.5 oC. (a) Suppose the tank is standing in the sun and reaches a temperature of
Using information in Appendices B and C, calculate the minimum number of grams of propane, C3H8(g), that must be combusted to provide the energy necessary to convert 5.50 kg of ice at -20 °C to
The vapor pressure of a volatile liquid can be determined by slowly bubbling a known volume of gas through it at a known temperature and pressure. In an experiment, 5.00 L of N2 gas is passed through
The relative humidity of air equals the ratio of the partial pressure of water in the air to the equilibrium vapor pressure of water at the same temperature times 100%. If the relative humidity of
For each of the two-dimensional structures shown here(a) Draw the unit cell,(b) Determine the type of two-dimensional lattice (from Figure 12.4), and (c) determine how many of each type of circle
Which type (or types) of crystalline solid is characterized by each of the following: (a) High mobility of electrons through out the solid; (b) Softness, relatively low melting point; (c) High
The electrical conductivity of titanium is approximately 2500 times greater than that of silicon. Titanium has a hexagonal close-packed structure, and silicon has the diamond structure. Explain how
Silicon carbide, SiC, has the three-dimensional structure shown in the figure.(a) Name another compound that has the same structure. (b) Would you expect the bonding in SiC to be predominantly ionic,
Unlike metals, semiconductors increase their conductivity as you heat them (up to a point). Suggest an explanation?
Teflon® is a polymer formed by the polymerization of F2C === CF2. Draw the structure of a section of this polymer. What type of polymerization reaction is required to form it?
Hydrogen bonding between polyamide chains plays an important role in determining the properties of a nylon such as nylon 6, 6 (Table 12.5). Draw the structural formulas for two adjacent chains of
Explain why X-rays can be used to measure atomic distances in crystals but visible light cannot be used for this purpose?
In their study of X-ray diffraction, William and Lawrence Bragg determined that the relationship among the wavelength of the radiation ((), the angle at which the radiation is diffracted ((), and the
Germanium has the same structure as silicon, but the unit cell size is different because Ge and Si atoms are not the same size. If you were to repeat the experiment described in the previous problem
(a) The density of diamond [Figure 12.30(a)] is 3.5 g/cm3 and that of graphite [Figure 12.30(b)] is Based on the structure of buckminsterfullerene (Figure 12.47), what would you expect its density to
The valence band of a semiconductor is made up of bonding molecular orbitals and the conduction band of antibonding molecular orbitals. (a) Given this fact would you expect n-type doping to
Indicate the type of crystal (molecular, metallic, ionic, or covalent-network) each of the following would form upon solidification: (a) CaCO3, (b) Pt, (c) ZrO2 (melting point), (d) Table Sugar
The karat scale used to describe gold alloys is based on mass percentages. (a) If an alloy is formed that is 50 mol% silver and 50 mol% gold, what is the karat number of the alloy? Use Figure 12.18
Spinel is a mineral that contains 37.9% Al, 17.1% Mg, and 45.0% O, by mass, and has a density of 3.57 g/cm3. The unit cell is cubic with an edge length of 8.09 Å. How many atoms of each type are in
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