the central science of chemistry   The automobile fuel called...

the central science of chemistry

 

The automobile fuel called E85E85 consists of 85%% ethanol and 15%% gasoline. E85 can be used in the so-called flex-fuel vehicles (FFVs), which can use gasoline, ethanol, or a mix as fuels. Assume that gasoline consists of a mixture of octanes (different isomers of C8H18),C8H18), that the average heat of combustion of C8H18(l)C8H18(l) is 5400 kJ/molkJ/mol , and that gasoline has an average density of 0.70 g/mLg/mL . The density of ethanol is 0.79 g/mLg/mL . (a) By using the information given as well as data in Appendix C,C, compare the energy produced by combustion of 1.0 L of gasoline and of 1.0 . of ethanol. (b) Assume that the density and heat of combustion of E85 can be obtained by using 85%% of the values for ethanol and 15%% of the values for gasoline. How much energy could be released by the combustion of 1.0 L of E85? (mathbf{c} ) How many gallons of E85 would be needed to provide the same energy as 10 gal of gasoline? (d) If gasoline costs $3.88$3.88 per gallon in the United States, what is the break-even price per gallon of E85 if the same amount of energy is to be delivered?A sample of gas is contained in a cylinder-and-piston arrangement. It undergoes the change in state shown in the drawing. (a) Assume first that the cylinder and piston are perfect thermal insulators that do not allow heat to be transferred. What is the value of qq for the state change? What is the sign of ww for the state change? What can be said about ΔEΔE for the state change? (b) Now assume that the cylinder and piston are made up of a thermal conductor such as a metal. During the state change, the cylinder gets warmer to the touch. What is the sign of qq for the state change in this case? Describe the difference in the state of the system at the end of the process in the two cases. What can you say about the relative values of ΔE?ΔE?

 

Limestone stalactites and stalagmites are formed in caves by
the following reaction:
Ca2+(aq)+2HCO−3(aq)⟶CaCO3(s)+CO2(g)+H2O(l)Ca2+(aq)+2HCO3−(aq)⟶CaCO3(s)+CO2(g)+H2O(l)
If 1 molmol of CaCO3CaCO3 forms at 298 KK under 1 atm pressure, the
reaction performs 2.47 kJkJ of P−VP−V work, pushing back the atmo-
sphere as the gaseous CO2CO2 forms. At the same time, 3.95 kJkJ
of heat is absorbed from the environment. What are the
values of ΔHΔH and of ΔEΔE for this reaction?

Consider the systems shown in Figure 5.10. In one case the battery becomes completely discharged by running the current through a heater, and in the other case by running a fan. Both processes occur at constant pressure. In both cases the change in state of the system is the same: The battery goes from being fully charged to being fully discharged. Yet in one case the heat evolved is large, and in the other it is small. Is the enthalpy change the same in the two cases? If not, how can enthalpy be considered a state function? If it is, what can you say about the relationship between enthalpy change andqqin this case, as compared with others that we have considered?

 

A coffee-cup calorimeter of the type shown in Figure 5.18 contains 150.0 g of water at 25.1∘C.25.1∘C. A 121.0−g121.0−g block of copper metal is heated to 100.4∘C100.4∘C by putting it in a beaker of boiling water. The specific heat of Cu(s)Cu(s) is 0.385J/g−K0.385J/g−K . The Cu is added to the calorimeter, and after a time the contents of the cup reach a constant temperature of 30.1∘C30.1∘C (a) Determine the amount of heat, in J, lost by the copper block. (b) Determine the amount of heat gained by the water. The specific heat of water is 4.18J/g−K4.18J/g−K . (c) The difference between your answers for (a) and (b) is due to heat loss through the Styrofoam cups and the heat necessary to raise the temperature of the inner wall of the apparatus. The heat capacity of the calorimeter is the amount of heat necessary to raise the temperature of the apparatus (the cups and the stopper) by 1 K. Calculate the heat capacity of the calorimeter in J/K. (d)What would be the final temperature of the system if all the heat lost by the copper block were absorbed by the water in the calorimeter?

 

Three common hydrocarbons that contain four carbons are listed here, along with their standard enthalpies of formation:
(a) For each of these substances, calculate the molar enthalpy of combustion to CO2(g)CO2(g) and H2O(l).H2O(l). (b) Calculate the fuel value, in kk/g,kk/g, for each of these compounds. (mathbf{c} ) text { For } each hydrocarbon, determine the percentage of hydrogen by mass.( ( ) By comparing your answers for parts (b) and (c), propose a relationship between hydrogen content and fuel value in hydrocarbons.

It is estimated that the net amount of carbon dioxide fixed by photosynthesis on the landmass of Earth is 5.5×1016g/yr5.5×1016g/yr of CO2.CO2. Assume that all this carbon is converted into glucose. (a) Calculate the energy stored by photosynthesis on land per year, in kJ. (b) Calculate the average rate of conversion of solar energy into plant energy in megawatts, MW
(1W=1J/s).(1W=1J/s). A large nuclear power plant produces about
103MW.103MW. The energy of how many such nuclear power plants is equivalent to the solar energy conversion?

Consider the following unbalanced oxidation-reduction reactions in aqueous solution:
Ag+(aq)+Li(s)⟶Ag(s)+Li+(aq)Fe(s)+Na+(aq)⟶Fe2+(aq)+Na(s)K(s)+H2O(l)⟶KOH(aq)+H2(g)Ag+⁡(aq)+Li(s)⟶Ag(s)+Li+(aq)Fe(s)+Na+(aq)⟶Fe2+(aq)+Na(s)K(s)+H2O(l)⟶KOH(aq)+H2(g)
(a) Balance each of the reactions. (b) By using data in Appendix C,C, calculate ΔH∘ΔH∘ for each of the reactions. (c) Based on the values you obtain for ΔH∘,ΔH∘, which of the reactions would you expect to be thermodynamically favored? (d) Use the activity series to predict which of these reactions should occur. coo (Section 4.4 ) Are these results in accord with your conclusion in part (c) of this problem?

 

Consider the following acid-neutralization reactions involving the strong base NaOH(aq)NaOH(aq) :
HNO3(aq)+NaOH(aq)⟶NaNO3(aq)+H2O(l)HCl(aq)+NaOH(aq)⟶NaCl(aq)+H2O(l)NH+4(aq)+NaOH(aq)⟶NH3(aq)+Na+(aq)+H2O(l)HNO3(aq)+NaOH(aq)⟶NaNO3(aq)+H2O(l)HCl(aq)+NaOH(aq)⟶NaCl(aq)+H2O(l)NH4+(aq)+NaOH(aq)⟶NH3(aq)+Na+(aq)+H2O(l)(a) By using data in Appendix CC , calculate ΔH∘ΔH∘ for each of the reactions. (b) As we saw in Section 4.3,4.3, nitric acid and hydrochloric acid are strong acids. Write net ionic equations = for the neutralization of these acids. (c) Compare the values of ΔH∘ΔH∘ for the first two reactions. What can you conclude? (d) In the third equation NH+4(aq)NH4+(aq) is acting as an acid. Based on the value of ΔH∘ΔH∘ for this reaction, do you think it is a strong or a weak acid? Explain.

Consider two solutions, the first being 50.0 mLmL of 1.00 MCuSO4MCuSO4 and the second 50.0 mLmL of 2.00 MKOHMKOH . When the two solutions are mixed in a constant-pressure calorimeter, a precipitate forms and the temperature of the mixture rises from 21.5 to 27.7∘C27.7∘C (a) Before mixing, how many grams of Cu are present in the solution of CuSO4CuSO4 ? (b) Predict the identity of the precipitate in the reaction. (c) Write complete and net ionic equations for the reaction that occurs when the two solutions are mixed. (d) From the calorimetric data, calculate ΔHΔH for the reaction that occurs on mixing. Assume that the calorimeter absorbs only a negligible quantity of heat, that the total volume of the solution is 100.0 mLmL , and that the specific heat and density of the solution after mixing are the same as those of pure water.

 

The methane molecule, CH4,CH4, has the geometry shown in Figure 2.17.2.17. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four C−HC−H bonds to infinity. We then have the process
CH4(g)⟶C(g)+4H(g)CH4(g)⟶C(g)+4H(g)
(a) Compare this process with the reverse of the reaction that represents the standard enthalpy of formation of CH4(g).(b)CH4(g).(b) Calculate the enthalpy change in each case. Which is the more endothermic process? What accounts for the difference in ΔH∘ΔH∘ values? (c) Suppose that 3.45 gg CH4(g)CH4(g) reacts with 1.22gF2(g),1.22gF2(g), forming CF4(g)CF4(g) and HF(g)HF(g) as sole products. What is the limiting reagent in this reaction? If the reaction occurs at constant pressure, what amount of heat is evolved?

 

One of the best-selling light, or low-calorie, beers is 4.2%% alcohol by volume and a 12 -oz serving contains 110 Calories; remember: 1 Calorie =1000=1000 cal =1=1 kcal. To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, C2H5OHC2H5OH , with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix CC to determine ΔHΔH for this reaction. (c)(c) If 4.2%% of the total volume is ethanol and the density of ethanol is 0.789g/mL,0.789g/mL, what mass of ethanol does a 12 - oz serving of light beer contain? (boldsymbol{d} ) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the 110 Calories comes from the ethanol?

 

(a) The electrostatic force (not energy) of attraction between two oppositely charged objects is given by the equation F=κ(Q1Q2/d2)F=κ(Q1Q2/d2) where κ=8.99×109N−m2/C2,Q1κ=8.99×109N−m2/C2,Q1 and Q2Q2 are the charges of the two objects in Coulombs, and dd is the distance separating the two objects in meters. What is the electrostatic force of attraction (in Newtons) between an electron and a proton that are separated by 1.00×1021.00×102 pm? (b) The force of gravity acting between two objects is given by the equation F=G(m1m2/d2),F=G(m1m2/d2), where GG is the gravitational constant, G=6.674×10−11N−m2/kg2,m1G=6.674×10−11N−m2/kg2,m1 and m2m2 are the masses of the two objects, and dd is the distance separating them. What is the gravitational force of attraction (in Newtons) between the electron and proton? (c) How many times larger is the electrostatic force of attraction?

 

(a) What is the electrostatic potential energy (in joules) between two protons that are separated by 62 pm? (b) What is the change in potential energy if the distance separating the two is increased to 1.0 nm? (c) Does the potential energy of the two particles increase or decrease when the distance is increased to 1.0 nm?

 

(a) What is the electrostatic potential energy (in joules) between an electron and a proton that are separated by 53 pm? (b) What is the change in potential energy if the distance separating the electron and proton is increased to 1.0 nm? (c) Does the potential energy of the two particles increase or decrease when the distance is increased to 1.0 nm?

 

You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer. (a) Assuming the pump and the air in it comprise the system, what is the sign of w when you compress the air? (b) What is the sign of qq for this process? (c) Based on your answers to parts (a) and (b), can you determine the sign of ΔEΔE for compressing the air in the pump? If not, what would you expect for the sign of ΔE?ΔE? What is your reasoning? [Section 5.2]]

Imagine a container placed in a tub of water, as depicted in the accompanying diagram. (a) If the contents of the container are the system and heat is able to flow through the container walls, what qualitative changes will occur in the temperatures of the system and in its surroundings? From the
system's perspective, is the process exothermic or endothermic? (b) If neither the volume nor the pressure of the system changes during the process, how is the change in internal energy related to the change in enthalpy? [Sections 5.2 and 5.3]