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engineering
chemical engineering

Questions and Answers of Chemical Engineering

The accompanying diagram shows how entropy varies with temperature for a substance that is a gas at the highest temperature shown.(a) What processes correspond to the entropy increases along the
Using Appendix C, compare the standard entropies at 25°C for the following pairs of substances: (a) CuO(s) and Cu2O(s) (b) 1 mol N2O4(g) and 2 mol NO2(g) (c) SiO2(s) and CO2(g) (d) CO(g) and CO2(g).
The standard entropies at 298 K for certain of the group 4A elements are as follows: C(s, diamond) = 2.43 J/mol-K, Si(s) = 18.81 J/mol - K, Ge(s) = 31.09 J/mol-K, and Sn(s) = 51.818 J/mol - K. All
Three of the forms of elemental carbon are graphite, diamond, and buckminsterfullerene. The entropies at 298 K for graphite and diamond are listed in Appendix C. (a) Account for the difference in the
Using S° values from Appendix C, calculate ΔS° values for the following reactions. In each case account for the sign of ΔS°. (a) C2H4(g) + H2 (g) → C2H6(g) (b) N2O4(g) → 2 NO2(g) (c) Be1OH2
Calculate Î”S° values for the following reactions by using tabulated values from Appendix C. In each case explain the sign of Î”S°.(c)
(a) For a process that occurs at constant temperature, express the change in Gibbs free energy in terms of changes in the enthalpy and entropy of the system. (b) For a certain process that occurs at
(a) What is the meaning of the standard free-energy change, ΔG°, as compared with ΔG? (b) For any process that occurs at constant temperature and pressure, what is the significance of ΔG = 0? (c)
For a certain chemical reaction, ΔH° = - 35.4 kJ and ΔH° = - 85.5 kJ. (a) Is the reaction exothermic or endothermic? (b) Does the reaction lead to an increase or decrease in the randomness or
A certain reaction has ΔH° = +23.7 kJ and ΔH° = +52.4 kJ. (a) Is the reaction exothermic or endothermic? (b) Does the reaction lead to an increase or decrease in the randomness or disorder of the
Using data in Appendix C, calculate Î”H°, Î”S°, and Î”G° at 298 K for each of the following reactions. In each case show that Î”G° =
Isomers are molecules that have the same chemical formula but different arrangements of atoms, as shown here for two isomers of pentane, C5H12.(a) Do you expect a significant difference in the
Use data in Appendix C to calculate Î”H°, Î”S°, and Î”G° at 25°C for each of the following reactions. In each case show that Î”G° =
Using data from Appendix C, calculate Î”G° for the following reactions. Indicate whether each reaction is spontaneous at 298 K under standard conditions.
Using data from Appendix C, calculate the change in Gibbs free energy for each of the following reactions. In each case indicate whether the reaction is spontaneous at 298 K under standard conditions.
Octane (C8H18) is a liquid hydrocarbon at room temperature that is the primary constituent of gasoline. (a) Write a balanced equation for the combustion of C8H18(l) to form CO2(g) and H2O(l). (b)
Sulfur dioxide reacts with strontium oxide as follows: SO2(g) + SrO(s) → SrSO3(s) (a) Without using thermochemical data, predict whether ΔG° for this reaction is more negative or less negative
Classify each of the following reactions as one of the four possible types summarized in Table 19.3:(a)(b) (c)
From the values given for Î”H° and Î”S°, calculate Î”G° for each of the following reactions at 298 K. If the reaction is not spontaneous under standard
A particular constant-pressure reaction is spontaneous at 390 K. The enthalpy change for the reaction is +23.7 kJ. What can you conclude about the sign and magnitude of ΔS for the reaction?
For a particular reaction, ΔH = -32 kJ and ΔH = - 98 kJ. Assume that and do not vary with temperature. (a) At what temperature will the reaction have ΔG = 0? (b) If T is increased from that in
The accompanying diagram shows how Î”H (red line) and TÎ”S(blue line) change with temperature for a hypothetical reaction.(a) What is the significance of the point at 300 K,
Reactions in which a substance decomposes by losing CO are called decarbonylation reactions. The decarbonylation of acetic acid proceeds as follows: CH3COOH(I) → CH3OH(g) + CO(g) By using data from
Consider the following reaction between oxides of nitrogen:NO2(g) + N2O(g) → 3 NO (g)(a) Use data in Appendix C to predict how ΔG° for the reaction varies with increasing temperature.(b)
Methanol (CH3OH) can be made by the controlled oxidation of methane:CH4(g) + 1/2O2(g) → CH3OH(g)(a) Use data in Appendix C to calculate ΔH° and ΔS° for this reaction.(b) How ΔG° is for the
(a) Use data in Appendix C to estimate the boiling point of benzene, C6H6(l). (b) Use a reference source, such as the CRC Handbook of Chemistry and Physics, to find the experimental boiling point of
(a) Using data in Appendix C, estimate the temperature at which the free-energy change for the transformation from I2(s) to I2(g) is zero. What assumptions must you make in arriving at this
Acetylene gas, C2H2(g), is used in welding.(a) Write a balanced equation for the combustion of acetylene gas to CO2(g) and H2O(l). (b) How much heat is produced in burning 1 mol of C2H2 under
The fuel in high-efficiency natural gas vehicles consists primarily of methane (CH4).(a) How much heat is produced in burning 1 mol of CH4(g) under standard conditions if reactants and products are
Explain qualitatively how Î”G changes for each of the following reactions as the partial pressure of O2 is increased:
Indicate whether Î”G increases, decreases, or does not change when the partial pressure of H2 is increased in each of the following reactions:
Consider the reaction 2 NO2(g) → N2O4(g). (a) Using data from Appendix C, calculate ΔG° at 298 K. (b) Calculate ΔG at 298 K if the partial pressures of NO2 and N2O4 are 0.40 atm and 1.60 atm,
The accompanying diagram shows how Î”G for a hypothetical reaction changes as temperature changes.(a) At what temperature is the system at equilibrium?(b) In what temperature range is the
Consider the reaction 3 CH4 (g) → C3H8(g) + 2 H2(g). (a) Using data from Appendix C, calculate ΔG° at 298 K. (b) Calculate ΔG at 298 K if the reaction mixture consists of 40.0 atm of CH4, 0.0100
Use data from Appendix C to calculate the equilibrium constant, K, at 298 K for each of the following reactions:
Using data from Appendix C, write the equilibrium-constant expression and calculate the value of the equilibrium constant for these reactions at 298 K:
Consider the decomposition of barium carbonate:Using data from Appendix C, calculate the equilibrium pressure of CO2 at (a) 298 K and (b) 1100 K.
Consider the reactionUsing data in Appendix C, calculate the equilibrium pressure of CO2 in the system at(a) 400 °C(b) 180 °C.
The value of Ka for nitrous acid (HNO2) at 25°C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Ka.
The Kb for methylamine (CH3NH2) at 25°C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Kb. (b) By using the value of Kb, calculate ΔG° for the
(a) Which of the thermodynamic quantities T, E, q, w, and S are state functions? (b) Which depend on the path taken from one state to another? (c) How many reversible paths are there between two
Indicate whether each of the following statements is true or false. If it is false, correct it. (a) The feasibility of manufacturing NH3 from N2 and H2 depends entirely on the value of for the
For each of the following processes, indicate whether the signs of ΔS and ΔH are expected to be positive, negative, or about zero. (a) A solid sublimes. (b) The temperature of a sample of Co(s) is
Consider a reaction A2(g) + B2(g) ‡† 2 AB(g), with atoms of A shown in red in the diagram and atoms of B shown in blue.(a) If Kc = 1, which box represents the system at equilibrium?(b) What
The reaction 2 Mg(s) + O2(g) → 2 MgO(s) is highly spontaneous and has a negative value for . The second law of thermodynamics states that in any spontaneous process there is always an increase in
Suppose four gas molecules are placed in the left flask in Figure 19.6(a). Initially, the right flask is evacuated and the stopcock is closed. (a) After the stopcock is opened, how many different
Consider a system that consists of two standard playing dice, with the state of the system defined by the sum of the values shown on the top faces.(a) The two arrangements of top faces shown here can
Ammonium nitrate dissolves spontaneously and endothermally in water at room temperature. What can you deduce about the sign of ΔS for this solution process?
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at
Trouton's rule states that for many liquids at their normal boiling points, the standard molar entropy of vaporization is about 88 J/mol-K. (a) Estimate the normal boiling point of bromine, Br2, by
For the majority of the compounds listed in Appendix C, the value of ΔG°f is more positive (or less negative) than the value of ΔG°f. (a) Explain this observation, using NH3(g), CCl4(l), and
Consider the following three reactions:(a) For each of the reactions, use data in Appendix C to calculate Î”H°, Î”G°, and Î”S° at 25°C.(b) Which of these reactions are spontaneous under
Using the data in Appendix C and given the pressures listed, calculate Î”G° for each of the following reactions:(a)(b)(c)
(a) For each of the following reactions, predict the sign of Î”H° and Î”S° and discuss briefly how these factors determine the magnitude of K.(b) Based on your general
Two different gases occupy the two bulbs shown here. Consider the process that occurs when the stopcock is opened, assuming the gases behave ideally.(a) Draw the final (equilibrium) state.(b) Predict
In the Bronsted-Lowry concept of acids and bases, acid-base reactions are viewed as proton-transfer reactions. The stronger the acid, the weaker is its conjugate base. In what ways are redox
Draw a generic picture of a fuel cell. What is the main difference between it and a battery, regardless of the redox reactions that occur inside?
Predict whether the following reactions will be spontaneous in acidic solution under standard conditions: (a) Oxidation of Sn to Sn2+ by I2 (to form I-) (b) Reduction of Ni2+ to Ni by I- (to form
Gold exists in two common positive oxidation states, +1 and +3. The standard reduction potentials for these oxidation states are(a) Can you use these data to explain why gold does not tarnish in the
A voltaic cell is constructed from an Ni2+ (aq) - Ni(s) half-cell and an Ag+(aq)-Ag(s) half-cell. The initial concentration of Ni2+ (aq) in the Ni2+ -Ni half-cell is [Ni2+] = 0.0100 M. The initial
A voltaic cell is constructed that uses the following half-cell reactions:The cell is operated at 298 K with [Cu+] = 0.20 M and [I-] = 3.5 M. (a) Determine E for the cell at these concentrations. (b)
Using data from Appendix E, calculate the equilibrium constant for the disproportionation of the copper(I) ion at room temperature: 2 Cu+(aq) → Cu2+ (aq) + Cu(s).
(a) Write the reactions for the discharge and charge of a nickel-cadmium (nicad) rechargeable battery.(b) Given the following reduction potentials, calculate the standard emf of the cell:(c) A
The capacity of batteries such as the typical AA alkaline battery is expressed in units of milliamp-hours (mAh). An AA alkaline battery yields a nominal capacity of 2850 mAh. (a) What quantity of
If you were going to apply a small potential to a steel ship resting in the water as a means of inhibiting corrosion, would you apply a negative or a positive charge? Explain.
(a) How many coulombs are required to plate a layer of chromium metal 0.25 mm thick on an auto bumper with a total area of 0.32 m2 from a solution containing CrO42-? The density of chromium metal is
Magnesium is obtained by electrolysis of molten MgCl2.
How does a zinc coating on iron protect the iron from unwanted oxidation?
Calculate the number of kilowatt-hours of electricity required to produce 1.0 × 103 kg (1 metric ton) of aluminum by electrolysis of Al3+ if the applied voltage is 4.50 V and the process is 45%
Some years ago a unique proposal was made to raise the Titanic. The plan involved placing pontoons within the ship using a surface-controlled submarine-type vessel. The pontoons would contain
The Haber process is the principal industrial route for converting nitrogen into ammonia: N2(g) + 3 H2(g) → 2 NH3(g) (a) What is being oxidized, and what is being reduced? (b) Using the
In a galvanic cell the cathode is an Ag+ (1.00 M) / Ag(s) half-cell. The anode is a standard hydrogen electrode immersed in a buffer solution containing 0.10 Mbenzoic acid (C6H5COOH) and 0.050 M
Consider the general oxidation of a species A in solution: A → A+ + e-. The term oxidation potential is sometimes used to describe the ease with which species A is oxidized- the easier a species is
A voltaic cell is based on Ag+ (aq) / Ag(s) and Fe3+(aq) / Fe2+ (aq) half-cells. (a) What is the standard emf of the cell? (b) Which reaction occurs at the cathode and which at the anode of the
Hydrogen gas has the potential as a clean fuel in reaction with oxygen. The relevant reaction is 2 H2(g) + O2(g) → 2 H2O(l) Consider two possible ways of utilizing this reaction as an electrical
Cytochrome, a complicated molecule that we will represent as CyFe2+, reacts with the air we breathe to supply energy required to synthesize adenosine triphosphate (ATP). The body uses ATP as an
The standard potential for the reduction of AgSCN(s) is + 0.0895 V. AgSCN(s) + e- → Ag(s) + SCN- (aq) Using this value and the electrode potential for Ag+ (aq), calculate the Ksp for AgSCN.
The Ksp value for PbS(s) is 8.0 × 10-28. By using this value together with an electrode potential from Appendix E, determine the value of the standard reduction potential for the reaction PbS(s) + 2
Magnesium is produced commercially by electrolysis from a molten salt using a cell similar to the one shown here.(a) What salt is used as the electrolyte?(b) Which electrode is the anode, and which
A student designs an ammeter (a device that measures electrical current) that is based on the electrolysis of water into hydrogen and oxygen gases. When electrical current of unknown magnitude is run
(a) What is meant by the term oxidation? (b) On which side of an oxidation half-reaction do the electrons appear? (c) What is meant by the term oxidant? (d) What is meant by the term oxidizing agent?
(a) What is meant by the term reduction? (b) On which side of a reduction half-reaction do the electrons appear? (c) What is meant by the term reductant? (d) What is meant by the term reducing agent?
Indicate whether each of the following statements is true or false: (a) If something is oxidized, it is formally losing electrons. (b) For the reaction Fe3+(aq) + Ci2+(aq) → Fe2+(aq) + Co3+(aq),
Indicate whether each of the following statements is true or false: (a) If something is reduced, it is formally losing electrons. (b) A reducing agent gets oxidized as it reacts. (c) Oxidizing agents
In each of the following balanced oxidation-reduction equations, identify those elements that undergo changes in oxidation number and indicate the magnitude of the change in each case. (a) I2O5(s) +
Indicate whether the following balanced equations involve oxidation-reduction. If they do, identify the elements that undergo changes in oxidation number. (a) PBr3(l) + 3 H2O(l) → H3PO3(aq) + 3
At 900°C titanium tetrachloride vapor reacts with molten magnesium metal to form solid titanium metal and molten magnesium chloride. (a) Write a balanced equation for this reaction. (b) What is
You may have heard that "antioxidants" are good for your health. Based on what you have learned in this chapter, what do you deduce an "antioxidant" is?
Hydrazine (N2H4) and dinitrogen tetroxide (N2O4) form a self-igniting mixture that has been used as a rocket propellant. The reaction products are N2 and H2O. (a) Write a balanced chemical equation
Complete and balance the following half-reactions. In each case indicate whether the half-reaction is an oxidation or a reduction.
Complete and balance the following half-reactions. In each case indicate whether the half-reaction is an oxidation or a reduction. Discuss.
Complete and balance the following equations, and identify the oxidizing and reducing agents:
Complete and balance the following equations, and identify the oxidizing and reducing agents. (Recall that the O atoms in hydrogen peroxide, H2O2, have an atypical oxidation state.)
(a) What are the similarities and differences between Figure 20.3 and Figure 20.4? (b) Why are Na+ ions drawn into the cathode half-cell as the voltaic cell shown in Figure 20.5 operates?
(a) What is the role of the porous glass disc shown in Figure 20.4? (b) Why do NO3- ions migrate into the anode half-cell as the voltaic cell shown in Figure 20.5 operates?
A voltaic cell similar to that shown in Figure 20.5 is constructed. One electrode half-cell consists of a silver strip placed in a solution of AgNO3, and the other has an iron strip placed in a
A voltaic cell similar to that shown in Figure 20.5 is constructed. One half-cell consists of an aluminum strip placed in a solution of Al(NO3)3, and the other has a nickel strip placed in a solution
(a) What does the term electromotive force mean? (b) What is the definition of the volt? (c) What does the term cell potential mean?
The diagram that follows represents a molecular view of a process occurring at an electrode in a voltaic cell.(a) Does the process represent oxidation or reduction? (b) Is the electrode the anode or
(a)Which electrode of a voltaic cell, the cathode or the anode, corresponds to the higher potential energy for the electrons? (b) What are the units for electrical potential? How does this unit

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