Chemistry Final Exam Study Questions
CO(g) + H2O(g) ⇄ CO2(g) + H2(g) Kc = 1.5 x 103 A 2.0 mol sample of CO(g) and a 2.0 mol sample of H2O(g) are introduced into a previously evacuated 100. L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium?
[CO2] > [CO]
The correct name for H2CO3(aq) is
carbonic acid
The entropy of the universe is _____.
continually increasing
Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are
different because S has a greater number of electron domains (regions of electron density) surrounding it than C.
The thermodynamic quantity that expresses the degree of disorder in a system is __________.
entropy
A reaction was found to be second order in carbon monoxide concentration. If the [CO] is doubled, then the rate should ____.
increase by a factor of 4
Elements in the same group have
the same outer electron configuration.
The value of Keq changes when
the temperature changes.
For the reaction C2H6 (g) → C2H4 (g) + H2 (g) ΔH° is +137 kJ/mol and ΔS° is +120 J/ K · mol. This reaction is __________.
thermodynamically favorable at high temperatures.
The synthesis of NH3 is represented by the equation above. Based on the equilibrium constant, K, and ΔH°rxn given above, which of the following can best be used to justify that the reaction is thermodynamically favorable at 298K and constant pressure?
ΔGo = -RT Ln K < 0 because K>>1
Substance ΔH°f(kJ/mol) Fe2O3(s) −826 CO(g) −111 Fe(s) 0 CO2(g) −394 Based on the information in the table above, which of the following expressions gives the approximate ΔH° for the reaction represented by the following balanced chemical equation? Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g)
ΔH°rxn=[2(0kJ/mol)+3(−394kJ/mol)]−[(−826kJ/mol)+3(−111kJ/mol)]
The standard Gibbs free energy of formation of __________ is zero. (a) H2O (l) (b) O (g) (c) H2 (g)
(c) only
2 h2o2(aq) -> 2 h2o(l) + o2 (g) E = 0.55 V The equation and standard cell potential for the decomposition of H2O2(aq) in acidic solution at 25°C is given above. The reduction half-reactions for the process are listed below. o2(g) + 4 h+(aq) + 4 e- -> 2 h2o(l) E = 1.23 V o2(g) + 2 h+(aq) + 2e- -> h2o2(aq) E = ? o2(g) + 2H+(aq) + 2e- -> h2o2(aq) What is the standard reduction potential for the half-reaction represented above
+0.68 V
H2(g) + 1/2 O2(g) -> H2O(l) DHf0 = -286 kJ 2 Na(s) + 1/2 O2(g) -> Na2O(s) DHf0 = -414 kJ Na(s) + 1/2 O2(g) + 1/2 H2(g) -> NaOH(s) DHf0= -425 kJ Based on the information above, what is the standard enthalpy change for the following reaction? Na2O(s) + H2O(l) -> 2 NaOH(s)
-150 kJ
The value of ΔS° for the oxidation of solid elemental sulfur to gaseous sulfur trioxide, 2S (s, rhombic) + 3O2 (g) → 2SO3 (g) is __________ J/K.
-166.4
3 C2H2(g) → C6H6(g) What is the standard enthalphy change ΔHo, for the reaction represented above? ΔHof of C2H2(g) is 230 kJ/ mol ΔHof of C6H6(g) is 83 kJ /mol
-607 kJ
The value of ΔH° for the formation of phosphorous trichloride from its constituent elements, P2 (g) + 3Cl2 (g) → 2PCl3 (g) is __________ kJ.
-720.5
The value of ΔG° at 25 oC for the decomposition of gaseous sulfur trioxide to solid elemental sulfur and gaseous oxygen, 2SO3 (g) → 2S (s, rhombic) + 3O2 (g) is __________ kJ.
-740.8
Given the data in the table below find DHrxn for the reaction: IF7(g) + I2(s)à IF5(g) + 2IF(g) Substance Hf 0 (kJ/mole) IF(g) -95 IF5(g) -840 IF7(g) -941
-89 kJ
3 Ag(s) + 4 HNO3(aq) → 3 AgNO3(aq) + NO(g) + 2 H2O(l) The reaction of silver metal and dilute nitric acid proceeds according to the equation above. If 0.10 mole of powdered silver is added to 10. milliliters of 6.0-molar nitric acid, the number of moles of NO gas that can be formed is
0.015 mol
A 1.0 L sample of an aqueous solution contains 0.10 mol of NaCl and 0.10 mol of CaCl2. What is the minimum number of moles of AgNO3 that must be added to the solution in order to precipitate all of the Cl- as AgCl(s) ? (Assume that AgCl is insoluble.)
0.30 mol
A necklace is gold plated using the following reaction: Au3+(aq) + 3e- à Au(s) What mass of gold would be plated out if a 0.13 A current is run through the solution for 1.50 hours?
0.47 g
Li2CO3.+ H2SO4(aq) → Li2SO4(aq) + H2O(l) + CO2(g) When the equation above is balanced and the coefficients are reduced to lowest whole-number terms, what is the coefficient of H2O(l)?
1
A 0.10 M solution of a weak monoprotic acid has a pH equal to 4.0. The ionization constant, Ka , of the acid is
1 x 10-7
Which of the following is an impossible electron configuration.
1s2 2s22p62d10 3s23p6
The correct answer (reported to the proper number of significant figures) to the following is __________. 6.4 × 3.26 = __________
21
In a saturated solution of Zn(OH)2 at 25°C, the value of [OH-] is 2.0 x 10-6 M. What is the value of the solubility-product constant, Ksp, for Zn(OH)2 at 25°C ?
4.0 x 10-18
Which of the following represents the ground state of an atom of nitrogen? A) ↑↓ ↑ ↑ ↑ B) ↑ ↑↓ ↑ ↑ C) ↑ ↑↑ ↑ ↑ D) ↑↓ ↑ ↑ _ E) ↑↓ ↑↓ ↑ ↑
A
Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms?
A.
Equal volumes of 0.1 M AgNO3(aq) and 2.0 M NH3(aq) are mixed and the reactions represented in the first 2 reactions above occur. Which Ag species will have the highest concentration in the equilibrium system shown in the third reaction above, and why?
Ag(NH3)2+(aq), because Keq3 = 1.6 x 107
What family or group would be used to identify the following compound H H | | H - C - C - N - H | | | H H H
Amine
Which of the following is considered inert?
Ar
Which diagram below would best represent a particulate model of sodium chloride?
B
ΔS is positive for the reaction __________.
BaF2 (s) → Ba2+ (aq) + 2F- (aq)
Which of the following is an example of a compound that has an exception to the octet rule?
BeCl2
A solution of a weak monoprotic acid is titrated with a solution of a strong base, KOH. Consider the points labeled (A) through (E) on the titration curve that results, as shown below. What letter represents the point at which the moles of the added strong base are equal to the moles of the weak acid initially present.
C
A sample of a compound that contains only the elements C, H, and N is completely burned in O2 to produce 44.0 g of CO2, 45.0 g of H2O, and some NO2. A possible empirical formula of the compound is
C2H5N
This molecule is non-polar.
CO2
Which transformation could take place at the cathode of an electrochemical cell?
CO2 → C2O42-
What is the chemical formula for calcium acetate?
Ca(C2H3O2)2
A solution containing HCl and the weak acid HClO2 has a pH of 2.4. Enough KOH(aq) is added to the solution to increase the pH to 10.5. The amount of which of the following species increases as the KOH(aq) is added?
ClO2-
Which of the following compounds is chromium(III) oxide?
Cr2O3
Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°?
D (the one selected in the pic)
Which of the following compounds is ionic?
Fe(OH)3
An unknown acid is dissolved in 25 mL of water and titrated with 0.100 M NaOH. The results are shown in the titration curve above. Which of the following could be the unknown acid?
Glycolic acid, pKa = 3.8
What is the formula for sulfurous acid?
H2SO3
Which element forms a compound having the formula K2XO4 ?
S
What causes the shielding effect to remain constant across a period?
The electrons are added to the same principal energy level.
A student was asked to formulate a hypothesis about what would happen if 100. mL of 0.1 M NaOH(aq) at 25°C was combined with 100. mL of 0.1 M MgCl2(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?
The resulting solution would contain a precipitate.
A sample of a solid labeled as NaCl may be impure. A student analyzes the sample and determines that it contains 75 % chlorine by mass. Pure NaCl(s) contains 61 % chlorine by mass. Which of the following statements is consistent with the data?
The sample contains NaCl(s) and LiCl(s).
The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) → 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstance? The salt bridge is replaced by a platinum wire.
Voltage becomes zero and remains at zero.
The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) → 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstance? A 50-milliliter sample of a 2-molar Cd(NO3)2 solution is added to the left beaker.
Voltage decreases but remains above zero.
The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) → 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstance? Current is allowed to flow for 5 minutes.
Voltage decreases but remains above zero.
To determine the concentration of a NaOH(aq) solution, a student titrated a 50. mL sample with 0.10 M HCl(aq) . The reaction is represented by the equation above. The titration is monitored using a pH meter, and the experimental results are plotted in the graph below. A student mixes a 10.0 mL sample of 1.0 M NaOH(aq) with a 10.0 mL sample of 1.0 M HCl(aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0°C. If the final temperature of the mixture is 26.0°C, what is the experimental value of ? (Assume that the solution mixture has a specific heat of 4.2 J/(g•K) and a density of 1.0 g/mL.)
-50. kJ/mol
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l) In the reaction represented above, what is the total number of moles of reactants consumed when 1.00 mole of CO2(g) is produced?
2.00 mol
Ni(s)→Ni2+(aq)+2e− Ag+(aq)+e−→Ag(s) Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag+(aq) and Ni(s) based on the half-reactions represented above?
2Ag+(aq)+Ni(s)→2Ag(s)+Ni2+(aq)
HNO2(aq)⇌H+(αq)+NO2−(aq) Kα = 4.0×10−4 A buffer is made by mixing 50.0 mL of a 0.10 M sample of HNO2 with 50.0 mL of a 0.10 M NaNO2 solution. What is the approximate pH of the final buffer solution?
3.40
10 HI + 2 KMnO4 + 3 H2SO4 → 5 I2 + 2 MnSO4 + K2SO4 + 8 H2O According to the balanced equation above, how many moles of HI would be necessary to produce 2.5 mol of I2, starting with 4.0 mol of KMnO4 and 3.0 mol of H2SO4?
5.0 mol
2 H2O(l) ⇄ H3O+(aq) + OH-(aq) The autoionization of water is represented by the equation above. Values of pKw at various temperatures are listed in the table below. Temp pKw 0 14.9 10 14.5 20 14.2 30 13.8 40 13.5 Based on the information above, what is the pH of pure water at 40C?
6.75
½ H2(g) + ½ I2(s) → HI(g) ∆H = 26 kJ/molrxn ½ H2(g) + ½ I2(g) → HI(g) ∆H = -5.0 kJ/molrxn Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below? I2(s) → I2(g)
62 kJ/mol
2 KClO3(s) → 2 KCl(s) + 3 O2(g) What is the percentage yield of O2 if 12.3 g of KClO3 (molar mass 123 g) is decomposed to produce 3.2 g of O2 (molar mass 32 g) according to the equation above?
67 %
A 10. g cube of copper at a temperature T1 is placed in an insulated cup containing 10. g of water at a temperature T2 . If T1 > T2, which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J/(g·°C) and the specific heat of water is 4.18 J/(g·°C).)
A. The temperature of the copper changed more than the temperature of the water.
Refer to the following. The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous acid Ka = 1.2 x 10-2 hydrochloric acid Ka >> 1 lactic acid Ka = 1.4 x 10-8 propanoic Ka = 1.3 x 10-5 Which of the following is correctly identifies the acids?
Acid 1 is lactic acid because it dissociates to the smallest extent.
2 H2O(l) ⇄ H3O+(aq) + OH-(aq) The autoionization of water is represented by the equation above. Values of pKw at various temperatures are listed in the table below. Temp pKw 0 14.9 10 14.5 20 14.2 30 13.8 40 13.5 Based on the information above, which of the following statements is true?
As the temperature increases, the pH of pure water decreases.
PCl5(g) ⇄ PCl3(g) + Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. Additional Cl2(g) is injected into the system at equilibrium. Which of the following graphs best shows the rate of the reverse reaction as a function of time? (Assume that the time for injection and mixing of the additional Cl2(g) is negligible.)
B Kinda looks like this: |\____ ______|
Which of the following Lewis diagrams best represents the bonding in the N2O molecule, considering formal charges?
B ( :N≡N-Ö: ) -The O is meant to have 3 pairs of dots
An acetate buffer solution is prepared by combining 50. mL of 0.20 M acetic acid, HC2H3O2(aq), and 50. mL of 0.20 M sodium acetate, NaC2H3O2(aq). A 5.0 mL sample of 0.10 M NaOH(aq) is added to the buffer solution. Which of the following is a correct pairing of the acetate species present in greater concentration and of the pH of the solution after the NaOH(aq) is added? (The pKa of acetic acid is 4.7.)
C2H3O2-, pH>4.7
Of the following, the entropy of gaseous ______ is the largest at 25 °C and 1 atm
C2H6
Which of the following compound would have the highest percent hydrogen by mass? ( C 12 g/mol, H 1 g/mol)
C2H6
A compound is composed of 60% C, 10%H, and 32% O, and the molar mass is 102g/mol. What is the molecular formula for this compound?(C 12g/mol, H 1g/mol, O 16 g/mol)
C5H10O2
6. A compound has an empirical formula of CH2O and a molecular mass of 180 g/mole. What is the molecular formula of the compound?
C6H12O6
A reaction has the following mechanism: Step 1: A + B ® C + D Step 2: A + D ® C + E + B The intermediate in the reaction is:
D
Given the table of ionization energies for magnesium, what is the best reason for the large increase between the second and third ionization energies? Successive Ionization Energies for Magnesium (kJ/mol) IE1 IE2 IE3 IE4 738 1451 7724 10540
Electrons 1 and 2 are valence electrons. Electron 3 in an inner shell electron.
Which of the following has two lone pairs of electrons?
H2O
H3PO4 ⇄ H+ + H2PO4- Ka = 7.2 X 10-3 H2PO4- ⇄ H+ + HPO4 2- Ka = 6.3 X 10-8 HPO4 2- ⇄ H+ + PO4 3- Ka = 4.5 X 10-13 On the basis of the information above, a buffer with a pH = 9 can best be made by using
H2PO4- + HPO42-
2H2S(g) + CH4(g) ⇄ CS2(g) + 4H2(g) Kc = 3.4 x 10-4 A 0.10 mol sample of each of the four species in the reaction represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest concentration when the system reaches equilibrium?
H2S(g)
A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a meter and graphed as a function of the volume of 0.100 M NaOH added. At point R in the titration, which of the following species has the highest concentration?
HA
Which of the following compounds contains the largest percent oxygen by mass?
HNO3
C2H4(g) + H2(g) --> C2H6(g) 1. C2H4(g) is reduced by H2(g) in the presence of a solid platinum catalyst, as represented by the equation above. Factors that could affect the rate of the reaction include which of the following? I. Changes in the partial pressure of H2(g) II. Changes in the particle size of the platinum catalyst III. Changes in the temperature of the reaction system
I, II, and III
Fe3+(aq) + SCN-(aq) ⇄ Fe(SCN)2+(aq) For the reaction represented above, the value of the equilibrium constant, Keq, is 240 at 25°C. From this information, correct deductions about the reaction at 25°C include which of the following? I. The reaction is quite rapid. II. The product is favored over the reactants at equilibrium. III. The reaction is endothermic.
II only
Two pure elements react to form a compound. One element is an alkaline earth metal, X, and the other element is a halogen, Z. Which of the following is the most valid scientific claim that can be made about the compound?
It has the formula XZ2.
CO(g) + 2 H2(g) ⇄ CH3OH(g) Δ H < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. Which of the following explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased to 650 K?
Kc will decrease because the reaction is exothermic.
The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak 26 u at represents an isotope of which of the following elements?
Mg with 14 neutrons
A 29.0g sample of a compound contains 12.0g of Mg, 1.0g of H, and 16.0g of O. Which of the following is the empirical formula of the compound?
Mg(OH)2
1s2 2s2 2p6 3s2 3p3 Atoms of an element, X, have the electronic configuration shown above. The compound most likely formed with magnesium, Mg, is
Mg3X2
This substance undergoes ionic bonding.
MgO
H2(g) + I2(g) ⇄ 2 HI(g) At 450oC, 2.0 moles each of H2(g), I2(g), and HI(g) are combined in a 1.0 L rigid container. The value of Kc at 450oC is 50. Which of the following will occur as the system moves toward equilibrium?
More HI(g) will form.
Which of the following diatomic species would have the largest bond-dissociation energy?
N2
Which of the following has a trigonal-pyramidal molecular geometry?
NH3
Which transformation could take place at the anode of an electrochemical cell?
NO → NO3-
In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted by a change in the volume of the system at constant temperature?
NO(g) + O3(g) ß àNO2(g) + O2(g)
NaOH(aq) + HCl(aq) --> NaCl(aq) + H2O(l) To determine the concentration of a NaOH(aq) solution, a student titrated a 50. mL sample with 0.10 M HCl(aq) . The reaction is represented by the equation above. The titration is monitored using a pH meter, and the experimental results are plotted in the graph below At the point labeled R on the pH curve, which of the following ions are present in the reaction mixture at a concentration greater than 0.01 M ?
Na + and Cl − only
List the following atoms in order of increasing ionization energy: Li, Na, C, O, F.
Na<Li<C<O<F
The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) → 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstance? The silver electrode is made larger.
No change in voltage occurs.
Which element within any given period of the periodic table will have the highest ionization energy?
Noble Gas
This molecule has a DEN = 0. (Difference in electronegativity of zero.)
O2
What family or group does this organic compound belong? H O | || H - C - C - OH | H
Organic Acid?
2 H2O2(aq) → 2 H2O(l) + O2(g) ΔH° = −196 kJ/molrxn The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300. K and recorded the concentration of H2O2 as a function of time. The results are given in the table below. Which of the following identifies the element(s) being oxidized and reduced in the reaction?
Oxygen is both oxidized and reduced.
5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) Which element is being oxidized during the titration, and what is the element's change in oxidation number?
Oxygen, which changes from -1 to 0.
H3PO4 ⇄ H+ + H2PO4- Ka = 7.2 X 10-3 H2PO4- ⇄ H+ + HPO4 2- Ka = 6.3 X 10-8 HPO4 2- ⇄ H+ + PO4 3- Ka = 4.5 X 10-13 A solution is prepared by mixing 50 mL of 1 M NaH2PO4 with 50 mL of 1 M Na2HPO4. On the basis of the information above, which of the following species is present in the solution at the lowest concentration?
PO43-
A(aq) + 2 B(aq) ® 3 C(aq) + D(aq) For the reaction above, carried out in solution of 30°C, the following kinetic data were obtained: Experiment Initial conc. of Reactants Initial rate 1 A: 0.120 B: 0.120 0.500 2 A: 0.240 B: 120 2.00 3 A: 0.240 B: 0.480 8.00 What is the rate law for the reaction?
Rate = k [A]^2[B]
2HO2(g)→H2O2(g)+O2(g) 1. The reaction represented by the chemical equation shown above occurs in Earth's atmosphere. In an experiment, [HO2] was monitored over time and the data plotted as shown in the following graph. Based on the information, which of the following is the rate law expression for the reaction?
Rate=k[HO2]2
Based on the information below and periodic trends, which of the following is the best hypothesis regarding the oxide(s) formed by Rb? H H2O, H2O2 Li Li2O, Li2O2 Na Na2O, Na2O2, NaO2 K K2O, K2O2, KO2
Rb will form Rb2O, Rb2O2, and RbO2.
The reaction between SO2 and O2 is represented by the chemical equation above. The table provides the approximate absolute entropies, S°, for O2(g) and SO3(g). Which of the following mathematical expressions can be used to correctly calculate S° for SO2(g) ?
S = 1/2[187 + (2x257) - 205] J/(mol K)
For which of the following molecules are resonance structures necessary to describe the bonding satisfactorily?
SO2
Which of the following is a polar molecule?
SO2
Which of the following is best represented by two or more resonance forms?
SO2
The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?
Sr2+(aq)+SO42−(aq)→SrSO4(s)
Which of the following statements is false?
The actual value of E can be measured.
To the equilibrium system shown below, a little PCl3 is added. What happens? PCl5 <--> PCl3 + Cl2
The amount of PCl5 increases; Cl2 decreases.
2 SO3(g) ⇄ 2 SO2(g) + O2(g) After the equilibrium represented above is established, some pure O2(g) is injected into the reaction vessel at constant temperature. After equilibrium is reestablished, which of the following has a lower value compared to its value at the original equilibrium?
The amount of SO2(g) in the reaction vessel.
Which of the following scientific claims about the bond in the molecular compound HCl is most likely to be true?
The bond is polar.
The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaF and MgF2 is shown in the table above. On the basis of Coulomb's law, which of the following best helps to explain the large difference between the lattice energies of NaF and MgF2? Compound Lattice Energy NaF 930 MgF2 2980
The charge of the Na cation is less than that of the Mg cation.
Consider the following equilibrium: H2(g) + I2(g) ⇄ 2HI(g) ∆H = -71.9K Colorless purple colorless Which of the following would allow you to conclude that the system has reached equilibrium?
The color intensity remains constant.
A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water, and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g⋅°C).)
The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.
Step 1: H2(g)+ICl(g)→HI(g)+HCl(g) (slow) Step 2: HI(g)+ICl(g)→HCl(g)+I2(g) (fast) 1. Which of the following represents the overall chemical equation for the reaction and the rate law for elementary step 1?
The overall reaction is H2 (g)+2ICl(g)→2HCl(g)+I2 (g); the rate law for step 1 is rate=k[H2][ICl].
Refer to the following. The pH of solutions of four acids prepared at various concentrations were measured and recorded in the table above. The four acids are, in no particular order, chlorous, hydrochloric, lactic, and propanoic. A 25 mL sample of a 1.0 M solution of acid 1 is mixed with 25 mL of 0.50 M NaOH. Which of the following best explains what happens to the pH of the mixture when a few drops of 1.0 M HNO3 are added?
The pH of the mixture stays about the same because the conjugate base of acid 1 reacts with the added H3O+ ions.
Rxn Equilibrium Reactions @ 298K Keq 1 Br2(g)+Cl2(g)⇄2BrCl(g) 10. 2 N2(g)+O2(g)⇄2NO(g) 4.2×10−31 The table above shows data for two reactions carried out in two separate evacuated 1.0-liter rigid containers at constant temperature of 298K. To each container 0.50mol of the appropriate reactants was added, and the reaction was allowed to reach equilibrium. Based on this information, which of the following correctly compares the relative concentrations of BrCl and NO present inside their respective containers at equilibrium?
[BrCl]eq>[NO]eq because the much larger Keq for reaction 1 means that a much higher concentration of products will be present at equilibrium for reaction 1 compared with reaction 2.
The diagram above represents the equilibrium between the two isomers of C2H2Cl2, and the table provides the data collected in an experiment to determine its equilibrium constant, Kc, at 490K. In a second experiment done at the same temperature, [Z]eq≈1.0 M. Which of the following is the approximate equilibrium concentration of Y in the second experiment, and why?
[Y]eq≈1.5 M because the ratio [Z]eq/[Y]eq should remain constant when the reaction is done at the same temperature
2 H2O2(l) → 2 H2O(l) + O2(g) The exothermic process represented above is best classified as a
chemical change because covalent bonds are broken, and new covalent bonds are formed.
The following questions relate to the below information. XY2 → X + Y2 The equation above represents the decomposition of a compound XY2. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY2. The reaction is thermodynamically favorable under standard conditions at 298 K. Therefore, the value of ΔS° for the reaction must be
greater than ΔH°/298 K
Which of the following is LEAST effective in increasing the rate of a reaction?
increasing the pressure by adding an inert gas
A molecular solid coexists with its liquid phase at its melting point. The solid-liquid mixture is heated, but the temperature does not change while the solid is melting. The best explanation for this phenomenon is that the heat absorbed by the mixture
is used in overcoming the intermolecular attractions in the solid.
2 A(g) + B(g) → 2 C(g) 1. When the concentration of substance B in the reaction above is doubled, all other factors being held constant, it is found that the rate of the reaction remains unchanged. The most probable explanation for this observation is that
substance B is not involved in the rate-determined step of the mechanism, but is involved in subsequent steps.
FeF2(s) ⇄ Fe2+(aq) + 2 F-(aq) K1 = 2 × 10-6 F-(aq) + H+(aq) ⇄ HF(aq) K2 = 1 × 103 FeF2(s) + 2 H+(aq) ⇄ Fe2+(aq) + 2 HF(aq) K3 = ? On the basis of the information above, the dissolution of FeF2(s) in acidic solution is
thermodynamically favorable, because K3 > 1
A 2.00 mol sample of C2H5OH undergoes the phase transition illustrated in the diagram above. The molar enthalpy of vaporization, ΔHvap, of C2H5OH is +38.6k J/mol. Which of the following best identifies the change in enthalpy in the phase transition shown in the diagram?
−77.2 kJ
