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chemistry
physical chemistry

Questions and Answers of Physical Chemistry

Hydrogen, H2, is used as a rocket fuel. The hydrogen is burned in oxygen to produce water vapor. 2H2(g) + O2(g) → 2H2O(g); ∆H = –484 kJ What is the enthalpy change per gram of hydrogen?
Ammonia burns in the presence of a copper catalyst to form nitrogen gas. 4NH3(g) + 3O2(g) → 2N2(g) + 6H2O(g); ∆H = –1267 kJ What is the enthalpy change to burn 35.8 g of ammonia?
Define an exothermic reaction and an endothermic reaction. Give an example of each.
Hydrogen sulfide, H2S, is a foul-smelling gas. It burns to form sulfur dioxide. 2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O(g); ∆H = –1036 kJ Calculate the enthalpy change to burn 28.5 g of hydrogen
Propane, C3H8, is a common fuel gas. Use the following to calculate the grams of propane you would need to provide 369 kJ of heat. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g); ∆H = –2043 kJ
Ethanol, C2H5OH, is mixed with gasoline and sold as gasohol. Use the following to calculate the grams of ethanol needed to provide 358 kJ of heat. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g); ∆H =
You wish to heat water to make coffee. How much heat (in joules) must be used to raise the temperature of 0.180 kg of tap water (enough for one cup of coffee) from 19oC to 96oC (near the ideal
An iron skillet weighing 1.28 kg is heated on a stove to 178oC. Suppose the skillet is cooled to room temperature, 21oC. How much heat energy (in joules) must be removed to effect this cooling? The
When steam condenses to liquid water, 2.26 kJ of heat is released per gram. The heat from 168 g of steam is used to heat a room containing 6.44 × 104 g of air (20 ft × 12 ft × 8 ft). The specific
When ice at 0oC melts to liquid water at 0oC, it absorbs 0.334 kJ of heat per gram. Suppose the heat needed to melt 31.5 g of ice is absorbed from the water contained in a glass. If this water has a
When 15.3 g of sodium nitrate, NaNO3, was dissolved in water in a calorimeter, the temperature fell from 25.00oC to 21.56oC. If the heat capacity of the solution and the calorimeter is 1071 J/oC,
When 23.6 g of calcium chloride, CaCl2, was dissolved in water in a calorimeter, the temperature rose from 25.0oC to 38.7oC. If the heat capacity of the solution and the calorimeter is 1258 J/oC,
A sample of ethanol, C2H5OH, weighing 2.84 g was burned in an excess of oxygen in a bomb calorimeter. The temperature of the calorimeter rose from 25.00oC to 33.73oC. If the heat capacity of the
The internal energy of a substance is a state function. What does this mean?
A sample of benzene, C6H6, weighing 3.51 g was burned in an excess of oxygen in a bomb calorimeter. The temperature of the calorimeter rose from 25.00oC to 37.18oC. If the heat capacity of the
Hydrazine, N2H4, is a colorless liquid used as a rocket fuel. What is the enthalpy change for the process in which hydrazine is formed from its elements?N2(g) + 2H2(g) †’ N2H4(l)Use the
Hydrogen peroxide, H2O2, is a colorless liquid whose solutions are used as a bleach and an antiseptic. H2O2 can be prepared in a process whose overall change is H2(g) + O2(g) → H2O2(l) Calculate
Ammonia will burn in the presence of a platinum catalyst to produce nitric oxide, NO. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) What is the heat of reaction at constant pressure? Use the following
Hydrogen cyanide is a highly poisonous, volatile liquid. It can be prepared by the reaction CH4(g) + NH3(g) → HCN(g) + 3H2(g) What is the heat of reaction at constant pressure? Use the following
Compounds with carbon€“carbon double bonds, such as ethylene, C2H4, add hydrogen in a reaction called hydrogenation.C2H4(g) + H2(g) †’ C2H6(g)Calculate the enthalpy change for
Acetic acid, CH3COOH, is contained in vinegar. Suppose acetic acid was formed from its elements, according to the following equation:2C(graphite) + 2H2(g) + O2(g) †’ CH3COOH(l)Find the
The cooling effect of alcohol on the skin is due to its evaporation. Calculate the heat of vaporization of ethanol (ethyl alcohol), C2H5OH. C2H5OH(l) → C2H5OH(g); ∆H° = ? The standard enthalpy
Carbon tetrachloride, CCl4, is a liquid used as an industrial solvent and in the preparation of fluorocarbons. What is the heat of vaporization of carbon tetrachloride?CCl4(l) †’ CCl4(g);
Hydrogen sulfide gas is a poisonous gas with the odor of rotten eggs. It occurs in natural gas and is produced during the decay of organic matter, which contains sulfur. The gas burns in oxygen as
Carbon disulfide is a colorless liquid. When pure, it is nearly odorless, but the commercial product smells vile. Carbon disulfide is used in the manufacture of rayon and cellophane. The liquid burns
Iron is obtained from iron ore by reduction with carbon monoxide. The overall reaction is Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) Calculate the standard enthalpy change for this equation. See Appendix
The first step in the preparation of lead from its ore (galena, PbS) consists of roasting the ore. 2PbS(s) + 3O2(g) → 2SO2(g) + 2PbO(s) Calculate the standard enthalpy change for this reaction,
Hydrogen chloride gas dissolves in water to form hydrochloric acid (an ionic solution). Find ∆Ho for the above reaction. The data are given in Table 6.2.
Carbon dioxide from the atmosphere “weathers,” or dissolves, limestone (CaCO3) by the reaction CaCO3(s) + CO2(g) + H2O(l ) → CA2+(aq) + 2HCO3(aq) Obtain ∆Ho for this reaction. See Table 6.2
The Group IIA carbonates decompose when heated. For example, MgCO3(s) → MgO(s) + CO2(g) Use enthalpies of formation (see Appendix C) and calculate the heat required to decompose 10.0 g of magnesium
The Group IIA carbonates decompose when heated. For example, BaCO3(s) → BaO(s) + CO2(g) Use enthalpies of formation (see Appendix C) and calculate the heat required to decompose 10.0 g of barium
The energy, E, needed to move an object a distance d by applying a force F is E × F × d. What must be the SI unit of force if this equation is to be consistent with the SI unit of energy for E?
The potential energy of an object in the gravitational field of the earth is Ep × mgh. What must be the SI unit of g if this equation is to be consistent with the SI unit of energy for Ep?
Liquid hydrogen peroxide has been used as a propellant for rockets. Hydrogen peroxide decomposes into oxygen and water, giving off heat energy equal to 686 Btu per pound of propellant. What is this
Hydrogen is an ideal fuel in many respects; for example, the product of its combustion, water, is nonpolluting. The heat given off in burning hydrogen to gaseous water is 5.16 × 104 Btu per pound.
Niagara Falls has a height of 167 ft (American Falls). What is the potential energy in joules of 1.00 lb of water at the top of the falls if we take water at the bottom to have a potential energy of
Any object, be it a space satellite or a molecule, must attain an initial upward velocity of at least 11.2 km/s in order to escape the gravitational attraction of the earth. What would be the kinetic
When calcium carbonate, CaCO3 (the major constituent of limestone and seashells), is heated, it decomposes to calcium oxide (quicklime). CaCO3(s) → CaO(s) + CO2(g); ∆H = 177.9 kJ How much heat is
Calcium oxide (quicklime) reacts with water to produce calcium hydroxide (slaked lime). CaO(s) + H2O(l ) → Ca(OH)2(s); ∆H = –65.2 kJ The heat released by this reaction is sufficient to ignite
Formic acid, HCHO2, was first discovered in ants (formica is Latin for “ant”). In an experiment, 5.48 g of formic acid was burned at constant pressure. 2HCHO2(l ) + O2(g) → 2CO2(g) + 2H2O(l) If
Acetic acid, HC2H3O2, is the sour constituent of vinegar (acetum is Latin for “vinegar”). In an experiment, 3.58 g of acetic acid was burned. HC2H3O2(l ) + 2O2(g) → 2CO2(g) + 2H2O(l ) If 52.0
Suppose you mix 21.0 g of water at 52.7oC with 54.9 g of water at 31.5oC in an insulated cup. What is the maximum temperature of the solution after mixing?
Suppose you mix 20.5 g of water at 66.2oC with 45.4 g of water at 35.7oC in an insulated cup. What is the maximum temperature of the solution after mixing?
A piece of lead of mass 121.6 g was heated by an electrical coil. From the resistance of the coil, the current, and the time the current flowed, it was calculated that 235 J of heat was added to the
Urea, (NH2)2CO, is used as a fertilizer (see the accompanying molecular model). What is the molar concentration of an aqueous solution that is 3.42 m urea? The density of the solution is 1.045 g/mL.
An aqueous solution is 2.00 M urea. The density of the solution is 1.029 g/mL. What is the molal concentration of urea in the solution?
Naphthalene, C10H8, is used to make mothballs. Suppose a solution is made by dissolving 0.515 g of naphthalene in 60.8 g of chloroform, CHCl3. Calculate the vapor-pressure lowering of chloroform at
How many grams of ethylene glycol, CH2OHCH2OH, must be added to 37.8 g of water to give a freezing point of –0.150°C?
A 0.930-g sample of ascorbic acid (vitamin C) was dissolved in 95.0 g of water. The concentration of ascorbic acid, as determined by freezing-point depression, was 0.0555 m. What is the molecular
A 0.205-g sample of white phosphorus was dissolved in 25.0 g of carbon disulfide, CS2. The boiling-point elevation of the carbon disulfide solution was found to be 0.159°C. What is the molecular
Calculate the osmotic pressure at 20°C of an aqueous solution containing 5.0 g of sucrose, C12H22O11, in 100.0 mL of solution.
Estimate the boiling point of a 0.050 m aqueous MgCl2 solution. Assume a value of i based on the formula.
A liter of water at 25°C dissolves 0.0404 g O2 when the partial pressure of the oxygen is 1.00 atm. What is the solubility of oxygen from air, in which the partial pressure of O2 is 159 mmHg?
An experiment calls for 35.0 g of hydrochloric acid that is 20.2% HCl by mass. How many grams of HCl is this? How many grams of water?
Toluene, C6H5CH3, is a liquid compound similar to benzene, C6H6. It is the starting material for other substances, including trinitrotoluene (TNT). Find the molality of toluene in a solution that
Calculate the mole fractions of toluene and benzene in the solution described in Exercise 12.6.Exercise 12.6Toluene, C6H5CH3, is a liquid compound similar to benzene, C6H6. It is the starting
A solution is 0.120 m methanol dissolved in ethanol. Calculate the mole fractions of methanol, CH3OH, and ethanol, C2H5OH, in the solution.
A solution is 0.250 mole fraction methanol, CH3OH, and 0.750 mole fraction ethanol, C2H5OH. What is the molality of methanol in the solution?
Identify the solute(s) and solvent(s) in the following solutions.a. 80 g of Cr and 5 g of Mob. 5 g of MgCl2 dissolved in 1000 g of H2Oc. 39% N2, 41% Ar, and the rest O2
The hypothetical ionic compound AB2 is very soluble in water. Another hypothetical ionic compound, CB2, is only slightly soluble in water. The lattice energies for these compounds are about the same.
Most fish have a very difficult time surviving at elevations much above 3500 m. How could Henry’s law be used to account for this fact?
Suppose you need to boil a water-based solution at a temperature lower than 100°C. What kind of liquid could you add to the water to make this happen?
Explain why pickles are stored in a brine (salt) solution. What would the pickles look like if they were stored in water?
Each of the following substances is dissolved in a separate 10.0-L container of water: 1.5 mol NaCl, 1.3 mol Na2SO4, 2.0 mol MgCl2, and 2.0 mol KBr. Without doing extensive calculations, rank the
If electrodes that are connected to a direct current (DC) source are dipped into a beaker of collodial iron(III) hydroxide, a precipitate collects at the negative electrode. Explain why this happens.
Give one example of each: a gaseous solution, a liquid solution, a solid solution.
Pressure has an effect on the solubility of oxygen in water but a negligible effect on the solubility of sugar in water. Why?
Maltose, C12H22O11, is a sugar produced by malting (sprouting) grain. A solution of maltose at 25°C has an osmotic pressure of 5.50 atm. What is the molar concentration of maltose?
Which aqueous solution has the lower freezing point, 0.10 m CaCl2 or 0.10 m glucose?
Which aqueous solution has the lower boiling point, 0.10 m KCl or 0.10 m CaCl2?
Commercially, sulfuric acid is obtained as a 98% solution. If this solution is 18 M, what is its density? What is its molality?
Phosphoric acid is usually obtained as an 85% phosphoric acid solution. If it is 15 M, what is the density of this solution? What is its molality?
A compound of manganese, carbon, and oxygen contains 28.17% Mn and 30.80% C. When 0.125 g of this compound is dissolved in 5.38 g of cyclohexane, the solution freezes at 5.28°C. What is the
A compound of cobalt, carbon, and oxygen contains 28.10% C and 34.47% Co. When 0.147 g of this compound is dissolved in 6.72 g of cyclohexane, the solution freezes at 5.23°C. What is the molecular
The carbohydrate digitoxose contains 48.64% carbon and 8.16% hydrogen. The addition of 18.0 g of this compound to 100. g of water gives a solution that has a freezing point of -2.2°C. a. What is the
Analysis of a compound gave 39.50% C, 2.21% H, and 58.30% Cl. When 0.855 g of this solid was dissolved in 7.50 g of naphthalene, the solution had a freezing point of 78.0°C. The pure solvent freezes
Fish blood has an osmotic pressure equal to that of seawater. If seawater freezes at 2.3°C, what is the osmotic pressure of the blood at 25°C? To solve this problem, what assumptions must be made?
Four ways were discussed to express the concentration of a solute in solution. Identify them and define each concentration unit.
A salt solution has an osmotic pressure of 17 atmospheres at 22°C. What is the freezing point of this solution? What assumptions must be made to solve this problem?
What is the difference between normal hemoglobin and the hemoglobin associated with sickle-cell anemia? How does this affect the solubility of the hemoglobin?
What tends to happen to the hemoglobin in a blood cell of a person who has sickle-cell anemia? How does this affect the shape and oxygen-carrying capacity of the cell?
How are phospholipids similar in structure to a soap molecule? What structural difference accounts for the fact that phospholipids form lipid bilayers rather than the micelles that soaps form?
How have chemists used these phospholipids to form “the world’s smallest test tubes”? Describe how these phospholipid vesicles might be used.
When 79.3 g of a particular compound is dissolved in 0.878 kg of water at 1 atm pressure, the solution freezes at 1.34°C. If the compound does not undergo ionization in solution and is nonvolatile,
What is the boiling point of a solution made by adding 6.69 g of magnesium chloride to 243.3 g of water? Use the formula of the salt to obtain i.
At 15°C and a partial pressure of 2.14 atm, the solubility of an unknown gas in a liquid is 15.6 g/L. What is the solubility of the gas in the liquid when the partial pressure of the gas is 24.6
Methanol, CH3OH, is a compound that is used in car windshield washer fluid to lower the freezing point of the solution. If an aqueous solution of windshield washer fluid has a mole fraction of
How many grams of potassium chloride must be added to 372 g of water in order to prepare a 0.110 m potassium chloride solution?
When two beakers containing different concentrations of a solute in water are placed in a closed cabinet for a time, one beaker gains solvent and the other loses it, so that the concentrations of
Although somewhat toxic, barium chloride has been used as a cardiac stimulant. Calculate the number of moles of barium chloride in 427 g of a 3.17% by mass barium chloride solution?
Ethanol, CH3CH2OH, is known as grain alcohol and is the alcohol found in alcoholic beverages. Calculate the mole fraction of ethanol in a solution that contains 4.76 g of ethanol dissolved in 50.0 g
A starch has a molar mass of 3.20 × 1004 g/mol. If 0.759 g of this starch is dissolved in 112 mL of solution, what is the osmotic pressure, in torr, at 25.00°C?
An aqueous solution is 0.797 M magnesium chloride. Given that the density of the solution is 1.108 g/mL, what is the molality of magnesium chloride in this solution?
A CaCl2 solution at 25°C has an osmotic pressure of 16 atm and a density of 1.108 g/mL. What is the freezing point of this solution?
An experimenter makes up a solution of 0.375 mol Na2CO3, 0.125 mol Ca(NO3)2, and 0.200 mol AgNO3 in 2.000 L of water solution. Note any precipitations that occur, writing a balanced equation for
An experimenter makes up a solution of 0.310 mol Na3PO4, 0.100 mol Ca(NO3)2, and 0.150 mol AgNO3 in 4.000 L of water solution. Note any precipitations that occur, writing a balanced equation for
The lattice enthalpy of sodium chloride, ∆H° for NaCl(s) → Na+(g) + Cl(g)
The lattice enthalpy of potassium chloride is 717 kJ/mol; the heat of solution in making up 1 M KCl(aq) is +18.0 kJ/mol. Using the value for the heat of hydration of Cl given in Problem 12.125,
A solution is made up by dissolving 15.0 g MgSO4∙7H2O in 100.0 g of water. What is the molality of MgSO4 in this solution?
Explain the process of fractional distillation to separate a solution of two liquids into pure components.

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