1) Solve the following problem.
H2(g) + CO2(g) <===> H2O(g) + CO(g)
When H2(g) is mixed with CO2(g) at 2,000 K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.
[H2] = 0.20 mol/L
[CO2] = 0.30 mol/L
[H2O] = [CO] = 0.55 mol/L
(a) What is the mole fraction of CO(g) in the equilibrium mixture?
(b) Using the equilibrium concentrations given above, calculate the value of Kc, the equilibrium constant for the reaction.
(c) Determine Kp, in terms of Kc for this system.
(d) When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g) is converted back to CO2(g). Calculate the value of Kc at this lower temperature.
(e) In a different experiment, 0.50 mole of H2(g) is mixed with 0.50 mole of CO2(g) in a 3.0-liter reaction vessel at 2,000 K. Calculate the equilibrium concentration, in moles per liter, of CO(g) at this temperature.
2) Propane, C3H8, is a hydrocarbon that is commonly used as fuel for cooking.
(a) Write a balanced equation for the complete combustion of propane gas, which yields CO2(g) and H2O(l)
(b) Calculate the volume of air at 30°C and 1.00 atmosphere that is needed to burn completely 10.0 grams of propane. Assume that air is 21.0 percent O2 by volume.
(c) The heat of combustion of propane is -2,220.1 kJ/mol. Calculate the heat of formation, DH°f, of propane given that DH°f of H2O(l) = -285.3 kJ/mol and DH°f of CO2(g) = -393.5 kJ/mol.
(d) Assuming that all of the heat evolved in burning 30.0 grams of propane is transferred to 8.00 kilograms of water (specific heat = 4.18 J/g ⋅ K), calculate the increase in temperature of the water.
3) A sample of dolomitic limestone containing only CaCO3 and MgCO3 was analyzed.
(a) When a 0.2800 gram sample of this limestone was decomposed by heating, 75.0 milliliters of CO2 at 750 mm Hg, and 20°C were evolved. How many grams of CO2 were produced?
(b) Write equations for the decomposition of both carbonates described above.
(c) It was also determined that the initial sample contained 0.0448 gram of calcium. What percent of the limestone by mass was CaCO3?
(d) How many grams of the magnesium-containing product were present in the sample in (a) after it had been heated?
4) Give the formulas to show the reactants and the products for FIVE of the following chemical reactions. Each of the reactions occurs in aqueous solution unless otherwise indicated. Represent substances in solution as ions if the substance is extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. In all cases a reaction occurs. You need not balance.
Example: A strip of magnesium is added to a solution of silver nitrate.
Mg + Ag+ ---> Mg2+ + Ag
(a) Ethanol is burned in oxygen.
(b) Solid barium oxide is added to distilled water.
(c) Chlorine gas is bubbled into a cold, dilute solution of potassium hydroxide.
(d) A solution of iron(II) nitrate is exposed to air for an extended period of time.
(e) Excess concentrated sulfuric acid is added to solid calcium phosphate.
(f) Hydrogen sulfide gas is bubbled into a solution of mercury(II) chloride.
(g) Solid calcium hydride is added to distilled water.
(h) A bar of zinc metal is immersed in a solution of copper(II) sulfate.
5) The conductivity of several substances was tested using the apparatus represented by the diagram below. The results of the tests are summarized in the following data table.
AgNO3 Sucrose Na H2SO4 Melting Liquid at Point 212° 185° 99° Room Temp. (°C) Liquid ++ - ++ + (fused) Water ++ - ++(1) ++(2) solution Solid - - ++ Not Tested Key: ++ Good conductor (1) Dissolves, accompanied by evolution of flammable gas + Poor conductor (2) Conduction increases as the acid is added slowly and carefully to water - Nonconductor
Using models of chemical bonding and atomic or molecular structure, account for the differences in conductivity between the two samples in each of the following pairs.
(a) Sucrose solution and silver nitrate solution
(b) Solid silver nitrate and solid sodium metal
(c) Liquid (fused) sucrose and liquid (fused) silver nitrate
(d) Liquid (concentrated) sulfuric acid and sulfuric acid solution
The phase diagram for a pure substance is shown above. Use this diagram and your knowledge about changes of phase to answer the following questions.
(a) What does point V represent? What characteristics are specific to the system only at point V?
(b) What does each point on the curve between V and W represent?
(c) Describe the changes that the system undergoes as the temperature slowly increases from X to Y to Z at 1.0 atmosphere.
(d) In a solid-liquid mixture of this substance, will the solid float or sink? Explain.
7) Explain the following in terms of the electronic structure and bonding of the compounds considered.
(a) Liquid oxygen is attracted to a strong magnet, whereas liquid nitrogen is not.
(b) The SO2 molecule has a dipole moment, whereas the CO2 molecule has no dipole moment. Include the Lewis (electron-dot) structures in your explanation.
(c) Halides of cobalt(II) are colored, whereas halides of zinc(II) are colorless.
(d) A crystal of high purity silicon is a poor conductor of electricity; however, the conductivity increases when a small amount of arsenic is incorporated (doped) into the crystal.
8) Lead iodide is a dense, golden yellow, slightly soluble solid. At 25°C, lead iodide dissolves in water forming a system represented by the following equation.
PbI2(s) <===> Pb2+ + 2 I¯ DH = +46.5 kilojoules
The solubility-product constant, Ksp, for PbI2 is 7.1 x 10¯9 at 25°C.
(a) How does the entropy of the system PbI2(s) + H2O(l) change as PbI2(s) dissolves in water at 25°C? Explain.
(b) If the temperature of the system were lowered from 25°C to 15°C, what would be the effect on the value of Ksp? Explain.
(c) If additional solid PbI2 were added to the system at equilibrium, what would be the effect on the concentration of I¯ in the solution? Explain.
(d) At equilibrium, DG = O. What is the initial effect on the value of DG of adding a small amount of Pb(NO3)2 to the system at equilibrium? Explain.
(I) A2 + B2 ---> 2 AB
(II) X2 + Y2 ---> 2 XY
Two reactions are represented above. The potential-energy diagram for reaction I is shown below. The potential energy of the reactants in reaction II is also indicated on the diagram. Reaction II is endothermic, and the activation energy of reaction I is greater than that of reaction II.
(a) Complete the potential-energy diagram for reaction II on the graph above.
(b) For reaction I, predict how each of the following is affected as the temperature is increased by 20°C. Explain the basis for each prediction.
(i) Rate of reaction
(ii) Heat of reaction
(c) For reaction II, the form of the rate law is rate = k[X2]m[Y2]n. Briefly describe an experiment that can be conducted in order to determine the values of m and n in the rate law for the reaction.
(d) From the information given, determine which reaction initially proceeds at the faster rate under the same conditions of concentration and temperature. Justify your answer.
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