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chemistry a molecular approach
Questions and Answers of
Chemistry A Molecular Approach
Find ΔG°rxn for the reaction:Use the following reactions with known ΔG°rxn values: 3 C(s) + 4H₂(g) → C3H8(g)
A reaction is spontaneous under a certain set of conditions. What can you conclude about ΔGrxn and Q? (a) AGxn < 0, Q > K (c) AGrxn > 0, Q< K (b) AGxn 0, Q > K
Find ΔG°rxn for the reaction 2 A + B → 2 C from the given data. a) -401 kJ A B C2B C b) 509 kJ A AGxn 128 kJ AGxn = 455 kJ AGxn = -182 kJ c) 401 kJ = d) -509 kJ
The given reaction has a ΔG°rxn = 9.4 kJ at 25 °C. Find ΔGrxn when PNO2 = 0.115 atm and PNO = 9.7 atm at 25 °C. 3 NO₂(g) + H₂O(1) a) -12.3 kJ c) 31.1 kJ 2 HNO3(1) + NO(g) b) 21.7 x 10³
Based on its fundamental definition, explain why entropy is a measure of energy dispersion.
Use tabulated free energies of formation to calculate the equilibrium constant for the reaction at 298 K: N₂O4(8) 2 NO₂(g) ⇒
The reaction A(g) ⇌ B(g) has an equilibrium constant of Kp = 2.3 * 10-5. What can you conclude about the sign of ΔG°rxn for the reaction?a) ΔG°rxn = 0 b) ΔG°rxn is negative c) ΔG°rxn is
A reaction has an equilibrium constant of Kp = 0.018 at 25 °C. Find ΔG°rxn for the reaction at this temperature.a) -835 J b) -4.32 kJ c) -9.95 kJ d) 9.95 kJ
What happens to the entropy of a sample of matter when it changes state from a solid to a liquid? From a liquid to a gas?
Which distribution of six particles into three interconnected boxes has the highest entropy? a) b) c) d) o D 口 Da
Explain why water spontaneously freezes to form ice below 0 °C even though the entropy of the water decreases during the state transition. Why is the freezing of water not spontaneous above 0 °C?
Without doing any calculations, determine the signs of ΔSsys and ΔSsurr for each chemical reaction. In addition, predict under what temperatures (all temperatures, low temperatures, or high
Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each reaction.Appendix IIB a. 2 CO(g) + O₂(g) = 2 CO₂(g) b. 2 H₂S(g) = 2 H₂(g) + S₂(g)
Which process results in the increase in entropy of the universe?a) The cooling of a hot cup of coffee in room temperature airb) The evaporation of water from a desk at room temperaturec) The melting
Use data from Appendix IIB to calculate the equilibrium constants at 25 °C for each reaction. ΔG°f for BrCl(g) is -1.0 kJ/mol.Appendix IIB a. 2 NO₂(g) N₂O4(8) b. Br₂(g) + Cl₂(g) = 2 BrCI(g)
Estimate the value of the equilibrium constant at 655 K for each reaction in Problem 74. (ΔH °f for BrCl is 14.6 kJ/mol.)Problem 74Use data from Appendix IIB to calculate the equilibrium constants
Consider the reaction:Calculate ΔGrxn for the reaction at 25 °C under each of the following conditions:a. Standard conditionsb. At equilibriumc. PCH3OH = 1.0 atm; PCO = PH2 = 0.010 atm CO(g) + 2
Consider the reaction:The following data show the equilibrium constant for this reaction measured at several different temperatures. Use the data to find ΔH°rxn and ΔS°rxn for the reaction.
Consider the reaction:The following data show the equilibrium constant for this reaction measured at several different temperatures. Use the data to find ΔH°rxn and ΔS°rxn for the reaction. 2
The change in enthalpy (ΔH°rxn) for a reaction is -25.8 kJ/mol. The equilibrium constant for the reaction is 1.4 * 103 at 298 K. What is the equilibrium constant for the reaction at 655 K?
A reaction has an equilibrium constant of 8.5 * 103 at 298 K. At 755 K, the equilibrium constant is 0.65. Find ΔH°rxn for the reaction.
Determine the sign of ΔSsys for each process.a. Water boilingb. Water freezingc.
Determine the sign of ΔSsys for each process.a. Dry ice sublimingb. Dew formingc.
Our atmosphere is composed primarily of nitrogen and oxygen, which coexist at 25 °C without reacting to any significant extent.However, the two gases can react to form nitrogen monoxide according to
Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown here. Calculate ΔG° and Kp for this reaction at 25 °C and
Ethene (C2H4) can be halogenated by the reaction:where X2 can be Cl2, Br2, or I2. Use the thermodynamic data given to calculate ΔH°, ΔS°, ΔG°, and Kp for the halogenation reaction by each of
H2 reacts with the halogens (X2) according to the reaction:where X2 can be Cl2, Br2, or I2. Use the thermodynamic data in Appendix IIB to calculate ΔH°, ΔS°, ΔG°, and Kp for the reaction
Consider this reaction occurring at 298 K:a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°rxn.b. If a reaction mixture contains only N2O and NO2 at partial
Consider this reaction occurring at 298 K:a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°rxn.b. If BaCO3 is placed in an evacuated flask, what is the
These reactions are important in catalytic converters in automobiles. Calculate ΔG° for each at 298 K. Predict the effect of increasing temperature on the magnitude of ΔG°. a. 2 CO(g) + 2NO(g) b.
All the oxides of nitrogen have positive values of ΔG°f at 298 K, but only one common oxide of nitrogen has a positive ΔS°f. Identify that oxide of nitrogen without reference to thermodynamic
The values of ΔG°f for the hydrogen halides become less negative with increasing atomic number. The ΔG°f of HI is slightly positive. However, the trend in ΔS°f is to become more positive with
Dinitrogen tetroxide decomposes to nitrogen dioxide:At 298 K, a reaction vessel initially contains 0.100 atm of N2O4.When equilibrium is reached, 58% of the N2O4 has decomposed to NO2. What
Consider the reaction X2(g) → 2 X(g). When a vessel initially containing 755 torr of X2 comes to equilibrium at 298 K, the equilibrium partial pressure of X is 103 torr. The same reaction is
Indicate and explain the sign of ΔSuniv for each process. a. 2 H₂(g) + O₂(g) 2 H₂O(1) at 298 K b. the electrolysis of H₂O(1) to H₂(g) and O₂(g) at 298 K c. the growth of an oak tree from
The Haber process is very important for agriculture because it converts N2(g) from the atmosphere into bound nitrogen, which can be taken up and used by plants. The Haber process reaction is N2(g) +
Making a Nonspontaneous Process Spontaneous. The hydrolysis of ATP, shown in Problem 91, is often used to drive nonspontaneous processes—such as muscle contraction and protein synthesis—in living
A metal salt with the formula MCl2 crystallizes from water to form a solid with the composition MCl2 · 6 H·O. The equilibrium vapor pressure of water above this solid at 298 K is 18.3 mmHg. What is
The solubility of AgCl(s) in water at 25 °C is 1.33 * 10-5 mol/L and its ΔH° of solution is 65.7 kJ/mol. What is its solubility at 50.0 °C
Calculate the entropy of each state and rank the states in order of increasing entropy. (a) (b) (c)
Given the data, calculate ΔSvap for each of the first four liquids.(ΔSvap = ΔHvap/T, where T is in K)All four values should be close to each other. Predict whether the last two liquids in the
The salt ammonium nitrate can follow three modes of decomposition:(a) To HNO3(g) and NH3(g), (b) To N2O(g) and H2O(g), and (c) To N2(g), O2(g), and H2O(g). Calculate ΔG°rxn for each mode of
Which is more efficient, a butane lighter or an electric lighter (such as the ones traditionally found on the dashboard of automobiles)? Explain.
Which statement is true?a. A spontaneous reaction is always a fast reaction.b. A spontaneous reaction is always a slow reaction.c. The spontaneity of a reaction is not necessarily related to the
Consider the changes in the distribution of nine particles into three interconnected boxes shown here. Which has the most negative ΔS? ロロ ロ ■■ 0. C 1 ■
Which process is necessarily driven by an increase in the entropy of the surroundings?a. The condensation of waterb. The sublimation of dry icec. The freezing of water
Which statement is true?a. A reaction in which the entropy of the system increases can be spontaneous only if it is exothermic.b. A reaction in which the entropy of the system increases can be
Which process is spontaneous at 298 K?a. H2O(l) → H2O(g, 1 atm)b. H2O(l) → H2O(g, 0.10 atm)c. H2O(l) → H2O(g, 0.010 atm)
The free energy change of the reaction A(g) → B(g) is zero under certain conditions. The standard free energy change of the reaction is -42.5 kJ. Which statement must be true about the reaction?a.
The reaction A( g) → B(g) has an equilibrium constant of 5.8 and under certain conditions has Q = 336. What can you conclude about the sign of ΔG°rxn and ΔG°rxn for this reaction under these
Imagine that you roll two dice. Write down all the possible rolls that sum to 2. Write all the possible rolls that sum to 12. Write all the possible rolls that sum to 7. Which configuration has the
If you roll 1 million dice, what will be the average of all the dice? If there is a room with 1 million dice and they all have a 1 on the top face, and there is an earthquake strong enough to roll
Borax, sodium tetraborate decahydrate, is an important mineral found in dry lakebeds in California. It is used to make soap and glass, and it is also used as a preservative. You can use the values of
Not all processes in which the system increases in entropy are spontaneous. How can this observation be consistent with the second law? Provide an example and explain your answer in complete
Have each group member look up ΔH°f and S° for one substance in the reaction: 3 O2(g) + 6 H2(g) + 6 C(s, graphite) → C6H12O6(s, glucose). What is ΔH° for this reaction? What is ΔS° ? When is
Which statement best captures the difference between volts and amps?(a) The volt is a unit that quantifies the difference in electrical potential energy, and the amp is a unit that quantifies the
Balance the redox reaction equation (occurring in acidic solution) and choose the correct coefficients for each reactant and product. _VO₂+ (aq) + _Sn(s) + _H+ (aq) a) 2,1,4 c)
In electrochemistry, spontaneous redox reactions are used for what purpose?
Balance the redox equation:Al(s) + Cu2+(aq) → Al3+(aq) + Cu(s)
In a voltaic cell, in which direction do electrons flow?(a) From higher potential energy to lower potential energy (b) From the cathode to the anode (c) From lower potential energy to higher
In electrochemistry, what kind of reaction can be driven by electricity?
Use Table 20.1 to calculate E°cell for the reaction. 2 C1O₂(g) + Pb(s) a) 1.77 V c) 0.82 V 2 ClO₂ (aq) + Pb²+ (aq) b) 2.03 V d) 1.08 V
Which statement is true for voltaic cells?a) Electrons flow from the anode to the cathode.b) Electrons flow from the more negatively charged electrode to the more positively charged electrode.c)
Balance the redox equation:Fe2+(aq) + MnO4–(aq) → GENERAL PROCEDURE Fe3+(aq) + Mn2+(aq)
Use Table 20.1 to determine which statement is true of the voltaic cell pictured here.a) Sn is the anode; Ag is the cathode; electrons flow from left to right.b) Sn is the cathode; Ag is the anode;
An electrode has a negative electrode potential. Which statement is correct regarding the potential energy of an electron at this electrode?(a) An electron at this electrode has a lower potential
Give the basic definitions of oxidation and reduction and explain the basic procedure for balancing redox reactions.
Balance the equation occurring in basic solution: I (aq) + MnO4 (aq) I₂(aq) + MnO₂ (s)
Use tabulated standard electrode potentials to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25 °C. (The equation is balanced.) Al(s) +
Use Table 20.1 to determine which metal does not dissolve in hydrochloric acid (HCl).a) Zn b) Cd c) Cu d) Fe TABLE 20.1 Standard Electrode Potentials at 25 °C Reduction Half-Reaction High
Which metal dissolves in HNO3 but not in HCl?(a) Fe (b) Au (c) Ag
What reaction (oxidation or reduction) occurs at the anode of a voltaic cell? What is the sign of the anode? Do electrons flow toward or away from the anode?
Without calculating E°cell, predict whether each of the redox reactions is spontaneous.If the reaction is spontaneous as written, make a sketch of the electrochemical cell in which the reaction
The calculation revealed that the reaction is not spontaneous. Based on conceptual reasoning, which of the following best explains why I2 does not oxidize Br¯?(a) Br is more electronegative than I;
What reaction (oxidation or reduction) occurs at the cathode of a voltaic cell? What is the sign of the cathode? Do electrons flow toward or away from the cathode?
Use the tabulated electrode potentials to calculate ΔG° for the reactionIs the reaction spontaneous? I₂(s) + 2 Br (aq) 21 (aq) + Br₂(1)
The Zn/Zn2+ electrode has a standard electrode potential of E° = -0.76 V. How does the relative potential energy of an electron at the Zn/Zn2+ electrode compare to the potential energy of an
A redox reaction has an equilibrium constant of K = 1.2 * 103. Which statement is true regarding ΔG°rxn and E°cell for this reaction?(a) E°cell is positive and ΔG°rxn is positive.(b) E°cell is
Explain the purpose of a salt bridge in an electrochemical cell.
What unit is used to measure the magnitude of electrical current?What unit is used to measure the magnitude of a potential difference? Explain how electrical current and potential difference differ.
A redox reaction has an E°cell = -0.56 V. What can you conclude about the equilibrium constant (K) for the reaction? a) K < 1 d) Nothing b) K> 1 c) K = 0 can be concluded about K from Ecell.
Determine the cell potential for an electrochemical cell based on the following two half-reactions: Oxidation: Cu(s)- →>>> Cu²+ (aq, 0.010 M) + 2 e Reduction: MnO4 (aq, 2.0 M) + 4 H(aq, 1.0 M) + 3
In an electrochemical cell, Q = 0.0010 and K = 0.10. What can you conclude about Ecell and E°cell?(a) Ecell is positive and E°cell is negative.(b) Ecell is negative and E°cell is positive.(c) Both
Predict the half-reaction occurring at the anode and the half-reaction occurring at the cathode for electrolysis for each reaction.(a) A mixture of molten AlBr3 and MgBr2 (b) An aqueous solution of
Which statement is true for both electrolytic and voltaic cells?(a) The cell spontaneously produces a positive voltage.(b) Electrons flow from the anode to the cathode.(c) Oxidation occurs at the
Find Ecell for an electrochemical cell based on the following reaction with [MnO4¯] = 2.0 M, [H+] = 1.0 M, and [Ag+] = 0.010 M. E°cell for the reaction is +0.88 V. MnO4 (aq) + 4H+ (aq) + 3 Ag(s) a)
Gold can be plated out of a solution containing Au3+ according to the half-reaction:What mass of gold (in grams) is plated by a 25-minute flow of 5.5 A current? 3+ Au³+ (aq) + 3 e Au(s)
What is the definition of the standard cell potential (E°cell)? What does a large positive standard cell potential imply about the spontaneity of the redox reaction occurring in the cell? What does
Silver plating uses the reaction Ag+(aq) + e¯ → Ag(s). How many moles of electrons must pass through an electrolytic cell for silver plating in order to plate 3 moles of Ag?(a) 1 mole e¯(b) 2
Describe the basic features of a cell diagram (or line notation) for an electrochemical cell.
In an electrochemical cell, Q = 0.010 and K = 855. What can you conclude about Ecell and E°cell?a) Ecell is positive and E°cell is negative.b) Ecell is negative and E°cell is positive.c) Ecell and
Why do some electrochemical cells employ inert electrodes such as platinum?
Which reaction occurs at the anode of a lead storage battery? a) Zn(s) + 2 OH-(aq) Zn(OH)2(s) + 2 e- b) PbO₂(s) + HSO4 (aq) + 3 H(aq) + 2 e c) Pb(s) + HSO4 (aq) - d) O₂(g) + 2 H₂O(l) + 4
Which of these metals does not act as a sacrificial electrode for iron?(a) Cu (b) Mg (c) Zn (d) Mn
Which reaction could be used to generate electricity in a voltaic electrochemical cell? a) Pb²+ (aq) + Mg(s) → Mg2+ (aq) + Pb(s) b) Zn²+ (aq) + Sn(s) →→→ Sn²+ (aq) + Zn(s) c) NaCl(aq) +
Describe the standard hydrogen electrode (SHE) and explain its use in determining standard electrode potentials.
Is a spontaneous redox reaction obtained by pairing any reduction half-reaction with one listed above it or with one listed below it in Table 20.1? TABLE 20.1 Standard Electrode Potentials at 25
Which reaction occurs at the cathode of an electrolytic cell containing a mixture of molten KCl and ZnCl2? a) K(s)→→→→→K+ (1) + e¯ b) K¹ (1) + e K(s) c) Zn²+(1) + 2e →→→ Zn(s) d) 2
How is the cell potential of an electrochemical cell (E°cell) related to the potentials of the half-cells?
Copper is plated onto the cathode of an electrolytic cell containing CuCl2(aq). How long does it take to plate 111 mg of copper with a current of 3.8 A? a) 1.3 x 10³ s b) 44 s c) 89 s d) 22 s
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