CHEM 1B Joseph- Final Exam
For the reaction: PCl5(g) ⇌ PCl3(g) + Cl2(g) at 600.0 K, the equilibrium constant, KP, is 11.5. Suppose that 1.500 g of PCl5 (MW=208.22 g/mol) is placed in an evacuated 500.0 mL bulb, which is then heated to 600.0 K. What is the total pressure (in atm) in the bulb at equilibrium?
1.379697343 Convert grams PCl5 to moles, find P using PV=nRT, ICE table, solve for x, add equilibriums to get total
Which of the following 0.5 M aqueous solutions will have the highest pH at 25oC? a) KBr b) NaIO c) C5H4N
B KBr spectators, neutral IO^- ka= 2 x 10^-11 (lower ka, most basic) C5H4N ka=5.6 x 10^-6 exam 1v1
Consider the following reaction at equilibrium: N2 (g) + 3 H2 (g) <---> 2 NH3 (g) Which of the following can be done to increase the number of moles of NH3 present at equilibrium? a) Increase the volume of the container at constant T b) Decrease the volume of the container at constant T c) Neither (a) nor (b) will increase the number of moles of NH3 present at equilibrium
B to increase number of NH3 you have to make rxn shift right. Rxn will shift to side with fewest moles when pressure is increased. To increase pressure, decrease volume. quiz 1v2
The concentration of the products equals that of the reactants and is constant at equilibrium. Select one: True False
False concentration of products doesn't have to equal concentration of reactants to be at equilibrium EC quiz
Rank the following solutions in order of increasing pH I) KClO II) Na III)C6H5NHBr IV) NaF
III<II<IV<I exam 1v3
For the following reaction: H2 (g) + I2 (g) <---> 2 HI (g) an equilibrium mixture has the following composition: 𝑃𝐻2 = 0.35 atm, 𝑃𝐼2 = 1.35 atm, 𝑃𝐻𝐼 = 3.6 atm. In a separate experiment, a mixture is initially prepared with 𝑃𝐻2 = 0.85 atm, 𝑃𝐼2 = 0.25 atm, 𝑃𝐻𝐼 = 2.8 atm. In which direction must the reaction proceed for this mixture to reach equilibrium? a) To the left b) To the right c) The mixture with PH2 = 0.85 atm, PI2 = 0.25 atm, PHI = 2.8 atm is an equilibrium mixture
a kp=27.4 qp=36.9 kp < qp rxn shifts left quiz 1
In a solution of CH3COOH at 25oC, the acid has dissociated 0.73%. Calculate [CH3COOH] in this solution. a) 0.33 M b) 1.28×10-7 M c) 0.18 M d) 3.03 M e) 0.59 M
a CH3COOH <---> H+ + CH3COO- ICE table if 0.73% of A dissociated, then 99.27% remains at equilibrium. plug everything into Ka and solve for A exam 1v1
Determine K for the following reaction at 25oC: HNO2 + ClO- <---> NO2- + HClO a) 1.1×10^4 b) 8.8×10^-5 c) 1.4×10^-11 d) 2.9×10^-7 e) 6.3×10^6
a using Ka's of HNO2 and ClO-. Reverse by using 1/K. multiply together. exam 1v1
The molar solubility of Ca(OH)2 in 0.010 M KOH is 1.010-5 mol/L. What is the Ksp of Ca(OH)2? a) 1.010-9 b) 4.010-15 c) 1.010-10 d) 1.010-2 e) 1.010-12
a. Ca(OH)2(s) <---> Ca2+ + 2OH- ICE table molar solubility is x in a ksp ice table exam 1v2
Given the reaction: HClO2 + HPO42- <---> ClO2- + H2PO4- a. This reaction is product favored b. This reaction is reactant favored c. Cannot determine if the reaction is product or reactant favored.
a. K=reactant acid/product acid 1.2x10^-2/ 6.2x10^-8 =1.9x10^5 K>1 Product favored exam 1v3
A monoatomic ideal gas is heated at a constant pressure. Which of the following statements regarding this transformation is true? a. E < q b. E = q c. E > q
a. PV=nRT Increase T, then increase V w=-Pext ΔV if V is positive, w is negative ΔE=q+w; if w is negative then ΔE<q quiz 2v3
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C. Calculate ΔV. a. -5.87 L b. -6.11 L c. 6.11 L d. 5.87 L e. none of these
a. PV=nRT Vf-Vi exam 2v1
Calculate the mass of solid NH4NO3 (80.0 g/mol) that should be added to 350 mL of 0.55 M NH3 in order to prepare a buffer with a pH of 8.66 at 25oC. Assume no volume change upon addition of the solid. a) 60g b) 171g c) 0.75 g d) 4.0g e) 11g
a. Use H-H equation and solve for HA exam 1v2
Suppose you add 45 J of heat to a system, let it do 10. J of expansion work, and then return the system to its initial state by cooling and compression. Which statement is true for this process? a. The change in the internal energy for this process is zero. b. ΔH = 70. J c. The work done in compressing the system must exactly equal the work done by the system in the expansion step. d. ΔH<ΔE
a. a,b. ΔH=0, so state function c. work not state function d. Cp<Cv not true exam 2v1
For a monatomic ideal gas that is being compressed at constant pressure: a. ΔE>ΔH b. ΔE<ΔH c. ΔE=ΔH
a. compression =ΔV is negative Cp>Cv ΔE>ΔH quiz 2v2
At a constant pressure of 1 atm, a 100 g sample of H2O(g) at 172 oC is cooled to 100 oC and then completely condensed at 100 oC (the boiling point of water). Calculate the total work for this process. a. 20.5 kJ b. -26.5 kJ c. 203J d. 7.94 kJ e. -13.9 kJ
a. exam 2v3
Upon adding 100 mL of 0.1 M HCl to 100 mL of 0.1 M NH3, the resulting mixture will be a) acidic b) basic c) neutral
a. major species: H+, Cl-, NH3, H2O H+ + NH3 <---> NH4 B, D, A table NH4 remains; acid exam 1v1
At equilibrium a. ΔSuni = 0 b. ΔSsurr = 0 c. ΔSsys = 0 d. None of these
a. not spontaneous in either direction exam 2v3
A 50.0 mL sample of the weak acid HA is titrated with 0.1 M NaOH. The titration curve is shown below. Determine Ka of the weak acid HA. pH 12 10 |----- 8 | 6 |------| 4 ----| 2 0 10 20 30 40 50 60 (not given, pH= 5.8) a) 1.610-6 b) 3.210-10 c) 2.210-4 d) 6.3105 e) 4.510-8
a. pH at half-equivalence point =pka when titrating a weak acid with strong base. half equivalence point occurs at half the volume of equivalence point (25L) exam 1v1
A bomb calorimeter has a heat capacity of 2.24 kJ/K. When a 0.170 g sample of gas with a molar mass of 28.0 g/mol was burned in this calorimeter, the temperature increased by 2.19 K. Calculate the energy of combustion for 1 mol of this gas. a. -8.08 × 10^2 kJ/mol b. -4.91 kJ/mol c. -1.37 × 10^2 kJ/mol d. -0.0298 kJ/mol e. -2.89 × 10^1 kJ/mol
a. q= C calorimeter ΔT
A 0.500 g sample of a common fat, is combusted in a bomb calorimeter containing 2.50 kg of water. The heat capacity of the calorimeter was 428 J/oC. The measured temperature increase of the water was 1.559 oC. The specific heat of water 4.184 J/g•oC. Determine the heat of combustion per gram of fat in kJ. a. 33.9 kJ/g b. 8.49 kJ/g c. 1367 kJ/g d. 17.0 kJ/g e. 29.9 kJ/g
a. qrxn=qw + qcal divide by grams exam 2v3
Consider the following reaction at 298 K and 1 atm: 2 H2(g) + O2(g) --> 2H2O(g) ΔG = -229 kJ ΔS = -71 J/K At 1 atm, what temperatures will make this reaction spontaneous a. T < 3523 K b. T < 301 K, but not above c. T > 3523 K, but not below d. T > 301 K e. spontaneous at all temps
a. ΔG*=ΔH*-TΔS -229=ΔH-(298)(-0.071) ΔH=(-) and ΔS=(-) spontaneous at low temp 0= -250.2-T(-0.071) T=3523.9 exam 2v3
Which one of the following statements is CORRECT? a. The larger the heat capacity of an object, the more thermal energy it can store. b. The SI unit of specific heat capacity is calories per gram (cal/g). c. When heat is transferred from the surroundings to the system, q is negative. d. Heat is transferred from the system to the surroundings in an endothermic process. e. Specific heat capacity is a positive value for liquids and a negative value for solids.
a. q=mCΔT as C goes up so does q quiz 2v1
What is expected when the reaction shown below takes place in container outfitted with a movable piston at a constant pressure of 1 atm and a constant temperature of 25 oC? 2 C2H6(g) + 7 O2(g) --> 4 CO2(g) + 6 H2O(g) a. Work will be done by the system b. Work will be done on the system c. No work will be done
a. Δn= 10-9= +1 PV=nRT ΔV=t w=-Pext ΔV (-)(+)(+) w is negative system does work quiz 2v3
When heat is transferred from the surroundings to the system, q is positive. a. True b. False
a. True Chemists take the point of view of the system. System gains heat, q is positive quiz 2v2
The larger the heat capacity of an object, the more thermal energy it can store. a. True b. False
a. True q=mCΔT C (heat capacity) goes up q (thermal energy) goes up quiz 2v2
For the reaction: N2(g) + 2 O2(g) <---> 2 NO2(g), KC = 8.3 × 10-10 at 25°C. What is the concentration of N2 gas at equilibrium when at equilibrium the concentration of NO2 is twice the concentration of O2 gas? a. 2.4 × 10^9 M b. 4.8 × 10^9 M c. 4.2 × 10^-10 M d. 2.1 × 10^-10 M e. 8.3 × 10^-10 M
b 4[O2]^2 / [N2][O2]^2 N2= 4 / 8.3 x 10^-10 N2= 4.819 x 10^9 quiz 1 v3
What is the resulting pH when 0.005 moles of KOH is added to 0.100 L of a solution that is 0.100 M in H2PO4- and 0.100 M HPO42-? a. 5.20 b. 7.68 c. 5.60 d. 6.72 e. 7.20
b H2PO4- + OH- ---> HPO4- + H2O BDA, H-H equation exam 1v3
Consider the following reactions simultaneously at equilibrium in the same solution. PbS (s) <---> Pb2+ (aq) + S2- (aq) S2- (s) + H2O (l)<---> HS- (aq) + OH- (aq) HS- (aq) + H2O (l) <---> H2S(aq) + OH-(aq) What will happen when HNO3 is added to the solution at a constant temperature? a) The amount of PbS (s) will increase b) The amount of PbS (s) will decrease c) The amount of PbS (s) will not change
b HNO3 reacts w/ OH-, decreasing OH-. B and C shift right and S2- decreases. A shifts right because S2 decreased, decreasing the amount of PbS exam 1v1
When baking soda (NaHCO3)is heated it decomposes according to the following reaction: 2 NaHCO3(s) <----> Na2CO3(s) + H2O(g) + CO2(g) If sufficient baking soda is placed in a container and heated to 90°C, the total pressure of the gases is 0.339 atm. What is the value of KP at that temperature? a. 0.339 b. 0.0287 c. 0.00144 d. 0.113 e. 0.170
b Ice table (ignore solids) Pt= x + x x= 0.1695 kp= (0.1695)(0.1695) quiz 1v3
In an aqueous solution of NH3 at 25oC, the equilibrium concentration of H+ is 4.3×10-12 M. Calculate the initial concentration of NH3 used in preparing this solution. a) 3.3×10-14 M b) 0.30 M c) 0.87 M d) 130M e) 2.6M
b NH3+H2O <---> OH- + NH4+ ICE table equal to Kb, find x through [OH-] = 10^-14/4.3x10^-12 solve for A exam 1v2
What combination of substances will give a solution buffered at a pH of 3.50 (at 25oC)? a) 1.26 M HNO2 and 1.00 M NaNO2 b) 1.00 M HNO2 and 1.26 M NaNO2 c) 1.00 M NaHCO3 and 0.661 M Na2CO3 d) 0.661 M NaHCO3 and 1.00 M Na2CO3 e) 3.16×10-4 M HCl and 3.16×10-4 M NaCl
b define buffers and test H-H equation until you find pH=3.5 exam 1v2
Consider the following endothermic reaction at equilibrium: CaCO3 (s) <----> CaO (s) + CO2 (g) Which of the following will decrease the value of KP for this reaction? a) Increase temperature at constant V b) Decrease temperature at constant V c) Neither (a) nor (b) will decrease the value of KP for this reaction
b endothermic=heat on left temp must decrease to make reaction shift left and decrease kp (reactant favored) quiz 1
A 79 mL solution of HCN and NaCN was prepared in which [HCN] = 1.6 M and [NaCN] = 1.7 M. To this solution, 34 mL of 1.0 M NaOH was added. What is the pH of the solution (at 25oC) after adding the NaOH? a) 9.21 b) 9.47 c) 8.95 d) 9.24 e) 9.18
b major species: HCN, Na+, CN-, OH-, H2O HCN + OH- <---> CN- B, D, A table use H-H with remaining species exam 1v1
Consider the following reaction: N2O4 (g) <---> 2 NO2 (g) K = 20.3 Into a 2.0 L container, we introduce 0.500 moles of N2O4 and 3.50 moles of NO2. Which direction will the reaction proceed to reach equilibrium? a) To the left b) To the right c) The reaction is already at equilibrium under these conditions
b use initial amounts in molarity (mol/L) to find Q. K>Q so rxn shifts right. quiz 1v2
At 25oC, a 1.0 M aqueous solution of NH4ClO will be a) Acidic b) Basic c) Neutral
b write two possible reactios NH4+ + H2O <---> NH3 + H3O+ Ka= 5.6 x 10^-10 ClO- + H2O <---> HClO + OH- Kb= 2.9 x 10^-7 Ka<Kb Higher Kb= basic exam 1v2
At what temperatures will a reaction be spontaneous if ΔH° = +45 kJ and ΔS° = +312 J/K? a. All temperatures below 144 K. b. All temperatures above 144 K. c. Temperatures between 45 K and 312 K. d. The reaction will be spontaneous at any temperature. e. The reaction will never be spontaneous.
b. G<0 to be spontaneous G= H* - TΔS* T= -H*/S* T=144K so spontaneous above this temp exam 2v1
Consider a sample containing 3.00 moles of a monatomic ideal gas at 35.0 oC and an initial pressure of 10.0 atm. Suppose the external pressure is lowered to 6.00 atm in a reversible, adiabatic manner. Calculate the final temperature. a. -28.5 oC b. -21.93 c. -21.9 oC d. 35.0 oC e. 28.5 oC
b. P1V1^➰=P2V2^➰ ➰=5/3 V1=nRT/P T2=P2V2/nR exam 2v3
Which one of the following statements is false? a. If qp for a process is negative, the process is exothermic. b. A bomb calorimeter measures ΔH directly. c. The change in enthalpy, ΔH, for a process is equal to the amount of heat absorbed at constant pressure, qp. d. The freezing of water is an example of an exothermic reaction. e. The change in internal energy, ΔE, for a process is equal to the amount of heat absorbed at constant volume, qv.
b. a bomb cal measures constant volume, not constant pressure. quiz 2v1
Which of the following statements is correct? a. The internal energy of a system decreases when work is done on the system and heat is flowing into the system. b. The system does work on the surroundings when an ideal gas expands against a constant external pressure. c. The internal energy of a system increases when more work is done by the system than heat is flowing into the system. d. All the statements are true. e. All the statements are false.
b. exam 2v1
For the reaction below at a certain temperature, it is found that the equilibrium concentrations in a 10 L rigid container are [H2] = 3.0 M, [Br2] = 1.5 M, and [HBr] = 2.5 M. H2 (g) + Br2 (g) <---> 2 HBr (g) If 15 moles of Br2 are added to this equilibrium mixture (assume constant volume and temperature), what will be the concentration of Br2 when equilibrium is re-established? a) 0.33 M b) 2.7M c) 3.3M d) 0.66 M e) 3.0M
b. find K, add 15mol/10L to Br2, ICE table, solve for x using K, 3-x=2.7M exam 1v2
Predict the relationship between KP and K for the following reaction at 300K. 2NOBr2 (g) <----> 2NO(g) + Br2 (l) a) KP<K b) KP=K c) KP>K
b. liquid doesn't count. 2 moles of gas on each side. Kp=K(RT)^delta n Kp=K(RT)^2-2 quiz 1
The equilibrium constant for the reaction N2(g) + O2(g) <--> 2NO(g) is 6.74 x 10^-16 at 25 oC and 1.49x 10^-9 at 100 oC. Determine the standard enthalpy of reaction. a. -56.0 kJ mol-1 b. 180 kJ mol-1 c. -4.00 kJ mol-1 d. 78.2 kJ mol-1 e. 4.00 kJ mol-1
b. ln (K2/K1)= -ΔH/R (1/T2-1/T1) exam 2v3
When 27.0 g of an unknown metal at 18.4 °C is placed in 70.0 g H2O at 79.5 °C, the water temperature decreases to 76.8 °C. What is the specific heat capacity of the metal? The specific heat capacity of water is 4.184 J/g⋅K. a. 0.34 J/g⋅K b. 0.50 J/g⋅K c. 0.74 J/g⋅K d. 0.94 J/g⋅K e. 1.4 J/g⋅K
b. q metal + q water = 0 mCΔT+mCΔT=0 solve for x quiz 2v2
Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is changed to 2.0 L while the pressure is kept constant, and then the pressure is increased to 2.00 atm while the volume remains constant. In the second sample, the opposite is done. The pressure is increased first, with constant volume, and then the volume is increased under constant pressure. Calculate the difference in q between the first sample and the second sample. a. -2.00 L•atm b. -1.00 L•atm c. 2.00 L•atm d. 1.00 L•atm e. none of these
b. q= qp+qv q1-q2 exam 2v1
A 0.1326 g sample of magnesium (Mg) was burned in an bomb calorimeter. The total heat capacity of calorimeter is 5.76 kJ/K. If the temperature rise of the calorimeter was 0.570 K, calculate the energy of combustion per mole of magnesium. a. 24.8 kJ/mol b. -602 kJ/mo1 c. 106 kJ/mol d. -24.8 kJ/mol e. 602 kJ/mo1
b. q=CcalΔT q/g= q/m x molar mass exam 2v2
Which of the following statements is CORRECT? a. If a reaction occurs at constant pressure, q = ∆E. b. If a reaction occurs at constant pressure, q = ∆H. c. If a reaction occurs at constant pressure, w = ∆E. d. If a reaction occurs at constant volume, ∆E > ∆H. e. If a reaction occurs at constant volume, w = ∆E.
b. quiz 2v1
Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following pathway. A (5.00 atm, 40.0 L) -> B (1.00 atm, 40.0 L) -> C (1.00 atm, 60.0 L) Suppose one starts in state A and does the above process (A>B>C) but returns the system back to A through state D (5.00 atm, 60.0 L), ie C>D > A. Which statement is true for the whole process? a. E > 0 b. E = 0 c. E < 0
b. return to the same place initial = final ΔE is a state function quiz 2v3
A 2.30 gram sample of KOH is added to enough water to make 2.50 L of solution. What is the pH of this solution at 25oC? a) 1.79 b) 12.6 c) 12.2 d) 1.39 e) 11.6
c 2.3 g (1/56.1g)(1/2.5L) = 0.016M OH- poH= -log[OH] 14-poH=pH exam 1v2
A 3.5 M aqueous solution of the weak acid HA has a pH of 4.3 (at 25oC). Calculate Ka of the weak acid. a) 1.4×10-5 b) 2.9×10-1 c) 7.2×10-10 d) 5.6×10-8 e) 5.0×10-5
c HA <---> H+ + A- ICE table use pH to find H+ plug everything into Ka exam 1v1
A 3.5 M aqueous solution of the weak acid HA has a pH of 4.3 (at 25oC). Calculate Ka of the weak acid. a) 1.4×10-5 b) 2.9×10-1 c) 7.2×10-10 d) 5.6×10-8 e) 5.0×10-5
c ICE table
Consider the following reaction: CaCO3 (s) <---> CaO (s) + CO2 (g) At equilibrium at a given temperature, 𝑃𝐶𝑂2 = 1.5 𝑎𝑡𝑚. The volume of the container is then doubled at constant temperature. Which of the following will be true when equilibrium is re-established? Assume the solids occupy negligible volume. a) 𝑃𝐶𝑂2>1.5𝑎𝑡𝑚 b) 𝑃𝐶𝑂2 <1.5𝑎𝑡𝑚 c) 𝑃𝐶𝑂2=1.5𝑎𝑡𝑚
c Kp is constant when T is constant even when volume changes. exam 1v2
Write the net ionic equation for the neutralization of HClO with KOH. a) H++OH- → H2O b) H+ +ClO- +K+ +OH- → H2O+K+ +ClO- c) HClO + OH- → H2O + ClO- d) HClO + KOH → H2O + KClO e) H++KOH→ H2O+K+
c major species: HClO, K+, OH-, H2O react OH with HClO exam 1v2
For a given equilibrium reaction, the forward rate of reaction is slower than the reverse rate of reaction. This means ___________. a) K>Q b) K=Q c) K<Q
c reaction will shift left if reverse rate is faster exam 1v1
What is the pH at the equivalence point of a weak acid-strong base titration? a. pH = 14.00 b. pH < 7 c. pH > 7 d. pH = 7
c strong base converted all to a weak base pH>7 exam 1v3
Assuming a constant temperature of 25oC, adding NaCH3COO to an aqueous solution of CH3COOH will: a) increase the pKa of CH3COOH. b) decrease the pKa of CH3COOH. c) not change the pKa of CH3COOH.
c. If T is constant, Ka is constant. If Ka is constant, pka is constant exam 1v1
Which statement is true? a. For an isothermal expansion, dividing the expansion into multiple steps does not change the amount of net work the system produces. b. A thermodynamically reversible process takes place infinitely fast. c. All real processes are irreversible. d. For an isothermal process, the heat equals the work e. All these statements are true.
c. a. more steps=more work b. speed is kinetic d. ΔE=0, q =-w exam 2v2
Addition of KClO3(s) to KClO3(s)<---> K+(aq) + ClO3-(aq) a. forward b. reverse c. neither (equilibrium)
c. adding solids will not shift the equilibrium exam 1v3
Consider the following reaction: 2 NH3 (g) <---->N2 (g) + 3 H2 (g) KP = 2.6×10-5 Initially, 2.5 atm of NH3 (g) are introduced into an otherwise empty container. At equilibrium, which of the following statements will be true? a) The rate of the reverse reaction will be greater than zero, but less than that of the forward reaction. b) The rate of the reverse reaction will be greater than zero, and greater than that of the forward reaction. c) The rate of the reverse reaction will be greater than zero, and equal to that of the forward reaction. d) The rate of the reverse reaction will be equal to zero, and equal to that of the forward reaction.
c. equilibrium means the forward rate of the reaction equals the reverse rate of the reaction quiz 1
When 40.11 g of CH4(g) reacts with excess Cl2(g) at constant pressure according to the chemical equation shown below, 1770. kJ of heat are released. Calculate the value of ΔH for the reaction given below. 2 CH4(g) + 3 Cl2(g) -> 2 CHCl3(l) + 3 H2(g) a. 1416 kJ b. -354.0 kJ c. -1416 kJ d. 707.9 kJ e. -707.9 kJ
c. q/mass x molar mass x mols quiz 2v3
Consider the following reaction: 2 NO(g) + O2(g) -> 2 NO2(g) Is the reaction endothermic or exothermic as written? ΔH= -112 kJ a. It is endothermic. b. This can't be determined without more information. c. It is exothermic.
c. since ΔH is negative, energy is leaving the system (product side) quiz 2v3
Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is changed to 2.0 L while the pressure is kept constant, and then the pressure is increased to 2.00 atm while the volume remains constant. In the second sample, the opposite is done. The pressure is increased first, with constant volume, and then the volume is increased under constant pressure. Calculate the difference in ΔE between the first sample and the second sample. a. 2.00 L•atm b. 4.50 L•atm c. 0 d. 1.00 L•atm e. none of these
c. ΔE is a state function independent of path exam 2v1
If ΔG° < 0 for a reaction at all temperatures, then ΔH° is ____ and ΔS° is ____. a. negative, negative b. positive, positive c. negative, positive d. positive, negative e. positive, either positive or negative
c. ΔG=ΔH*-TΔS* exam 2v1
Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following pathway. A (5.00 atm, 40.0 L) -> B (1.00 atm, 40.0 L) -> C (1.00 atm, 60.0 L) Calculate HAC (ie the total ΔH going from A to B to C) a. -120 L•atm b. -210 L•atm c. -350 L•atm d. -200 L•atm e. 315 L•atm
c. ΔH=nCpΔT ΔT= Δ(PV)/nR ΔH= n (5/2R (-140Latm/nR) quiz 2v3
Using the information below, calculate ΔH°f for C2H5OH(l). C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) ΔH°=-1367 kJ ΔH°f for CO2(g) = -393.5 kJ/mol ΔH°f for H2O(l) = -286 kJ/mol a. -688 kJ/mol b. -3.01 × 103 kJ/mol c. -278 kJ/mol d. 278 kJ/mol e. 688 kJ/mol
c. ΔHrxn= sum of products-reactants exam 2v1
Use the following thermodynamic data. H kJ/mol; S J/Kmol Fe: H=0, S= 27.8 O2: H=0, S=205.1 Fe2O3: H= -825.5, S =87.4 to calculate ΔS°universe for the formation of Fe2O3(s) at 298.2 K. 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) a. +2202.7 J/K b. -2202.7 J/K c. +4984.9 J/K d. -546.2 J/K e. +546.2 J/K
c. ΔS uni=ΔS sys + ΔS surr Δsys= products-reactants Δsurr = -ΔH/T ΔH= 2 x -825.5 kJ--> J divide by 1000 exam 2v2
Consider the following reaction: N2 (g) + 2 O2 (g) <----> 2 NO2 (g) K = 5.2×10-8 Initially, [N2] = 1.20 M, [O2] = 0.45 M, and [NO2] = 0.00 M. Calculate the concentration of NO2 at equilibrium. a) 5.6×10-5 M b) 7.9×10-5 M c) 1.6×10-4 M d) 1.1×10-4 M e) 2.40 M
d 4x^2/0.243=5.2x10^-8 NO2=2x 2x= 5.6x10^-5 NO2= 1.1x10^-4 quiz 1
A 64.5-mL sample of 0.15 M HNO2 is titrated with 0.12 M NaOH. What is the pH after 29.0 mL of NaOH has been added? a. 3.65 b. 2.95 c. 7.00 d. 3.15 e. 10.35
d HNO2 + OH- ---> NO2- + H20 weak acid and strong base before equilibrium point BDA, then H-H equation exam 1v3
Consider the following reaction: N2H4 (g) <---> 2 H2 (g) + N2 (g) Initially, 𝑃𝑁2𝐻4 = 3.20 atm, 𝑃𝐻2 = 2.30 atm, and 𝑃𝑁2 = 0.00 atm. At equilibrium, the total pressure in the container is 6.00 atm. What is the equilibrium pressure of H2? a) 0.50 atm b) 0.25 atm c) 2.30 atm d) 2.80 atm e) 2.55 atm
d ICE table then use P total is 6. P total = all pressures quiz 1v2
The pH of a 0.36 M solution of a weak acid is 4.3 at 25oC. Determine the percent dissociation of the weak acid in this solution at 25oC. a) 100% b) 0% c) 8.4% d) 0.014% e) 0.38%
d. %diss = amount dissociated (x in ICE)/initial x 100 5x10^-5/0.36 = 0.014%
Assume that reactant A can undergo the reaction shown below. A(aq) B(aq) If the equilibrium constant, K, is greater than 1.0, which of the following statements are correct? 1. The forward reaction is spontaneous. 2. The reaction favors the formation of products. 3. The forward rate of reaction is fast. a. 1 only b. 2 only c. 3 only d. 1 and 2 e. 1, 2, and 3
d. 1 K>1 spontaneous 2 K>1 product favored 3 needs kinetic energy exam 2v1
If 25.0 g H2O at 16.0 °C is combined with 70.0 g H2O at 85.5 °C, what is the final temperature of the mixture? The specific heat capacity of water is 4.184 J/g⋅K. a. 14.4 °C b. 34.3 °C c. 50.8 °C d. 67.2 °C e. 70.0 °C
d. 25(Tf-16)+70(Tf-85.5)=0 exam 2v1
A 50 mL sample of 1.0 M HCOOH is mixed with 50 mL of 1.0 M NaOH. Calculate the pH of the resulting mixture at 25oC. a) 5.28 b) 5.62 c) 7.00 d) 8.72 e) 8.38
d. BDA table, then ICE table, x=OH, poH=-log[OH] exam 1v2
Calculate the maximum mass of solid CaCO3 (100 g/mol) that can completely dissolve in 0.75 L of water at 25oC. The Ksp of CaCO3 at 25oC is 3.36×10-9. Assume the volume of the solid is negligible. a) 5.8×10-3 g b) 3.4×10-7 g c) 2.5×10-7 g d) 4.3×10-3 g e) 5.8×10-6 g
d. CaCo3(s)<-->Ca2+ + CO2-3 ICE table, find x from ksp, multiply by volume, multiply by molar mass exam 1v1
At what temperatures will a reaction be spontaneous if ΔH°rxn = -12.7 kJ and ΔS°rxn = +135 J/K? a. All temperatures below 94.1 K b. Temperatures between 12.7 K and 135 K c. All temperatures above 94.1 K d. The reaction will be spontaneous at any temperature. e. The reaction will never be spontaneous.
d. G will always be negative so spontaneous at all temperatures
The thermochemical equation for the combustion of benzene is shown below. 2 C6H6(l) + 15 O2(g) → 12 CO2(g) + 6 H 2O(g) ΔH°rxn = -3909.9 kJ/mol-rxn What is the enthalpy change for the combustion of 12.5 g C6H6? a. -626 kJ b. -1.22 × 10^4 kJ c. -2.44 × 10^4 kJ d. -313 kJ e. -4.89 × 10^4 kJ
d. find moles of C6H6 12.5/(78g) divide by n; multiply together; exam 2v1
At a certain temperature the equilibrium constant, KC, equals 0.11 for the reaction: 2 ICl(g) <---> I2(g) + Cl2(g). What is the equilibrium concentration of ICl if 0.75 mol of I2 and 0.75 mol of Cl2 are initially mixed in a 2.0-L flask? a. 0.23 M b. 0.28 M c. 1.1 M d. 0.45 M e. 0.56 M
d. ice table then set equilibrium expressions equal to Kc and solve for x then multiply by 2 quiz 1v3
At 1150 K the following reaction has a K of 0.365. Find the equilibrium constant for this reaction at 1260 K. 2 SO2(g) + O2(g) → 2 SO3(g) a. 0.366 b. 1.654 c. 0.0599 d. 2.225 e. None of these.
d. ln(K2/K1)= -ΔH*/R (1/t2 - 1/t1) find K2 exam 2v1
Calculate the standard enthalpy of formation, ΔH°f,for sulfur dioxide given the thermochemical equations below. 2 S(s) + 3 O2(g) → 2 SO3(g) ΔH°rxn = -791.5 kJ 2 SO2(g) + O2(g) → 2 SO3(g) ΔH°rxn = -197.9 kJ a. -494.7 kJ/mol b. -395.7 kJ/mol c. -593.6 kJ/mol d. -296.8 kJ/mol e. -989.4 kJ/mol
d. reverse second rxn (switch signs) and divide by number of moles exam 2v1
Consider the following information: 2 ClF + O2 <---> Cl2O + F2O K= 23.3 2ClF3 +2O2 <--->Cl2O+3F2O K=10.3 2 F2 + O2 <---> 2F2O K= 1.6x10^-3 Determine K for the reaction ClF + F2 <---> ClF3 a) 3.62×10^-3 b) 6.20×10^-1 c) 3.84×10^-1 d) 6.02×10-2 e) 6.50
d. take square root of K when dividing by 2 1/K when reversing reaction multiply all together exam 1v1
If a cylinder equipped with a piston expands against an external pressure of 1.25 atm, increasing the volume of a cylinder by 0.500 L and releasing 25.0 J of heat, what is ΔE for the process? a. -63.3 J b. 0.625 J c. 63.3 J d. -88.3 J e. -25.6 J
d. w=-P ext ΔV convert to J (x101.3 J/Latm) then ΔE= q+w Quiz 2v2
Which of the following mixtures will produce a buffer solution? a) 100mLof0.25MNaNO3and100mLof0.50MHNO3 b) 100mLof0.25MNaNO2and100mLof0.50MHNO2 c) 100 mL of 0.25 M NaOH and 100 mL of 0.50 M HNO2 d) Choices (b) and (c) are both buffers e) Choices (a), (b), and (c) are all buffers
d. you must have a weak acid/base and its conjugate to make a buffer solution exam 1v1
Consider the reaction2NO2(g) N2O4(g); ΔH° = -56.8 kJ ΔS° = -175 J/K In a container (at 298 K), N2O4(g) and NO2(g) are mixed with initial partial pressures of 2.4 atm and 0.42 atm, respectively. Which of the following statements is correct? a. The final total pressure must be known to answer this question. b. The system is at equilibrium at these initial pressures. c. Some NO2(g) will dimerize to form N2O4(g). d. Some N2O4(g) will decompose into NO2(g). e. None of these statements is correct.
d. ΔG=ΔG* + RTlnQ ΔG*=ΔH* - TΔS* ΔG=1817 J ΔG is positive, rxn goes backwards exam 2v1
Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following pathway from state A to B. A (3.00 atm, 20.0 L) → B (1.00 atm, 30.0 L)For a monatomic idea gas Cv =3/2R and Cp =5/2R. Calculate ∆H from state A to state B. a. 144 kJ b. -144 kJ c. 7.60 kJ d. -7.60 kJ e. -340 kJ
d. ΔH=nCpΔT ΔT= PfVf/nR - PiVi/nR quiz 2v1
Consider a process carried out on 1.00 mol of a monatomic ideal gas by the following pathway from state A to C. A (3.00 atm, 20.0 L) → B (3.00 atm, 30.0 L) → C (1.00 atm, 30.0 L) Calculate q from state A to state B. a. - 9.12 kJ b. - 2.53 kJ c. - 7.60 kJ d. 7.60 kJ e. 9.12 kJ
d. PΔV=nRΔT ΔT=PΔV/nR then q=nCpΔT
In an isothermal process, the pressure on 1 mol of an ideal monatomic gas suddenly changes from 4.00 atm to 100.0 atm at 25°C. Calculate w a. -59.5 kJ b. 23.5 kJ c. 0 d. 59.5 kJ e. -23.5 kJ
d. w= -PextΔV then change L/atm to J by multiplying by R/R x(8.3145/0.08206) exam 2v1
The acid dissociation constant for a weak acid HX at 29°C is 2.98 x 10^-8. Calculate the free energy of formation for X-(aq) at 29°C. The standard free energies of HX(aq) and H+(aq) at 29°C are -334.8 kJ/mol and 0, respectively. a. -378 kJ/mol b. 291 kJ/mol c. 378 kJ/mol d. -291 kJ/mol e. -316 kJ/mol
d. ΔG*=-RTlnK ΔG*= G*products-G*reactants exam 2v3
For a chemical system, ΔG°rxn and ΔGrxn are equal when a. the reactants and products are in the gas phase. b. the equilibrium constant, K, equals 0. c. the system is in equilibrium. d. the reactants and products are in standard state conditions. e. the reaction quotient, Q, is less than 1.
d. ΔG=ΔG* + RTlnQ RTlnQ means deviation from standard state. ΔG=ΔG* in standard state. exam 2v2
When NH4Cl is added to 0.10 M NH3, relative to the pH of a pure 0.10 M NH3 solution, the pH of the resulting solution will _______. (Assume the addition does not change the volume.) remain the same. increase. become 7. decrease.
decrease NH4+ makes rxn shift left, OH- goes down, pH goes down
Determine the pH (at 25oC) of an aqueous 0.15 M solution of KClO. a) 3.7 b) 4.1 c) 9.9 d) 13.2 e) 10.3
e ClO- + H2O <---> HClO + OH ICE table set equilibrium equal to Kb use OH to find pOH then pH exam 1v1
Of the following types of energy, which is/are classified as potential energy? I. chemical energy II. electrical energy III. gravitational energy a. 1 only b. 2 only c. 3 only d. 2 and 3 e. 1, 2, and 3
e.
What is the pH of a solution made by mixing 20.00 mL of 0.100 M HBr with 40.00 mL of 0.100 M NaOH? Assume that the volumes of the solutions are additive. a. 13.52 b. 11.30 c. 1.48 d. 0.48 e. 12.52
e. BDA H+ +OH- --> H2O 0.002/0.06L (total v) -log[OH]=poH exam 1v3
A sample of N2O4(g) is placed in an empty cylinder at 25 oC. After the equilibrium is reached, the total pressure is 1.5 atm, and 40% (by moles) of the original N2O4(g) has dissociated to NO2(g). Calculate the value of KP for this dissociation reaction at 25 oC. a. 1.00 b. 1.60 c. 1.33 d. 1.07 e. 1.14
e. N2O4 <--> 2NO2 ICE table, C is -0.40Y exam 1v3
For a particular process q = -10 kJ and w = 35 kJ. Which of the following statements is true? a. Heat flows from the surroundings to the system. b. The system does work on the surroundings. c. ∆E = -45 kJ d. All of these are true. e. None of these is true.
e. a. says q is positive b. says w is negative c. -10 + 35 = 25kJ quiz 2v1
All of the following statements concerning entropy are true EXCEPT a. a positive change in entropy denotes a change toward greater disorder. b. the entropy of a substance in the gas phase is greater than the solid phase. c. entropy values for substances are greater than or equal to zero. d. entropy is a state function. e. entropy is zero for elements under standard conditions.
e. enthalpy is 0 for elements under standard conditions. exam 2v1
Consider the equation A (aq) + 2 B (aq) <---> 3 C (aq) + 2 D (aq). 41.0 mL of a 0.054 M aqueous solution of A is mixed with 24.2 mL of a 0.109 M aqueous solution of B. At equilibrium, the concentration of C is 0.0406 M. Determine K for this reaction. a) 0.030 b) 2.7 c) 0.0020 d) 1.8×10-4 e) 0.013
e. find moles from L x mol/L for A and B. divide by total volume for new molarity. use ice table and solve for K. exam 1v1
Determine the major species in a solution prepared by mixing 15 mL of 1.0 M HCl with 25 mL of 1.0 M NH3. a) HCl, NH3, H2O b) H+, Cl-, NH4+, H2O c) NH4+, Cl-, H2O d) NH4+, NH3, H2O e) NH4+, Cl-, NH3, H2O
e. major species H+, Cl-, NH3, H2O H+ + NH3 ---> NH4 B, D, A determine species remaining exam 1v2
Which of the following thermodynamic quantities are state functions: heat (q), work (w), enthalpy change (∆H), and/or internal energy change (∆E)? a. ∆E only b. ∆H only c. w only d. q only e. ∆H and ∆E
e. only ones that are path independent state function: property independent of pathway
If 46.1 g Al at 21.0 °C is placed in 80.0 g H2O at 88.0 °C, what is the final temperature of the mixture? The specific heat capacities of aluminum and water are 0.897 J/g⋅K and 4.184 J/g⋅K, respectively. Assume the Al and water are the whole universe. a. 28.4 °C b. 39.2 °C c. 54.5 °C d. 69.8 °C e. 80.6 °C
e. q=-q, solve for Tf quiz 2v1
A 40 g sample of copper (specific heat = 0.385 J /g oC) is heated to 82.4 oC and added to 53 g of water (specific heat = 4.184 J /g oC) initially at 32.1 oC. What is the final temperature of the water? Assume no heat is lost to the surroundings. a. 28.3 oC b. 24.7 oC c. 40.6 oC d. 57.3 oC e. 35.4 oC
e. qmetal+qwater=0 initial metal: 82.4 initial water: 32.1 quiz 2v3
What is the conjugate acid of methylamine (CH3NH2)? a) CH3NH3 b) CH3NH c) CH3NH- d) CH3NH+ e) CH3NH3+
e. to find conjugate acid, add H+ exam 1v1
At 699 K, ΔG° = -23.25 kJ for the reaction H2(g) + I2(g) 2HI(g). Calculate ΔG for this reaction if the reagents are both supplied at 10.0 atm pressure and the product is at 1.00 atm pressure. a. +36.6 kJ b. -3.5 kJ c. +50.0 kJ d. -36.6 kJ e. -50.0 kJ
e. ΔG=ΔG*+RTlnQ Q= products/reactants exam 2v2
Which of the following are state functions? a. work, heat, enthalpy b. heat, enthalpy, energy c. work, heat, enthalpy, energy d. work, heat e. enthalpy, energy
e. ΔH and ΔE are state functions work and heat are not exam 2v1
For the following reaction at 298.2 K, 2 CO(g) + O2(g) → 2 CO2(g) calculate ΔS°(universe) given ΔS°(system) = -173.1 J/K and ΔH°(system) = -566.0 kJ. a. -2071.3 J/K b. -175.0 J/K c. -739.0 J/K d. -171.3 J/K e. +1725.0 J/K
e. ΔS* universe = ΔS*sys + ΔS*surr ΔS* sys + -ΔH/T exam 2v1
Thermodynamics can be used to determine all of the following EXCEPT a. the direction in which a reaction is spontaneous. b. the temperature at which a reaction is spontaneous. c. the extent to which a reaction occurs. d. the entropy change of a reaction. e. the rate of reaction
e. rate of reaction is kinetics exam 2v1
Consider the following reaction for the decomposition of ammonium nitrate at 480K: NH4NO3 (s) <---> N2O (g) + 2 H2O (g) Kp = 17.4 at 480K Calculate the maximum mass of NH4NO3 (80.0 g/mol) that can completely decompose in a 7.0 L container at 480K. Assume the solid occupies a negligible volume. a. 29.2 g b. 131g c. 36.8 g d. 247g e. 23.2 g
e. solve for PN2O which is x in the ICE table. Use this to find moles of PN2O with PV=nRT. Use mole ration to convert moles of N2O to moles of NH4NO3 and multiply by molar mass (80g/mol) to get maximum mass. exam 1v2
Consider the following reaction at equilibrium: 2NH3(g) ⇌ N2 (g) + 3H2 (g) The moles of H2 in the reaction container will increase with ________. I) some removal of NH3 from the reaction vessel (V and T constant) II) a decrease in the total pressure (T constant) III) an addition of helium gas (V and T constant) a. I only b. I, II & III c. II & III d. I & II e. none of these f. I & III g. III only h. II only
h EC quiz
Based on the equation below how much heat is required when 10.0 g of water completely evaporates? H2O(l) --> H2O(g) ΔH*rxn = 44.0 kJ a. 24.4 kJ b. 7920 kJ c. 440 kJ d. 79.3 kJ
q. find moles g/molar mass multiply by ΔH*rxn exam 2v2
Consider the following exothermic reaction shown to you in class as a demo at 25 °C and 1 atm. 2K(s) + 2H2O(l) --> 2KOH(aq) + H2(g) Find signs for ΔE ΔG ΔH w
ΔE (-) ΔG (-) ΔH (-) w (-) ΔE=q(-) + w(-) ΔG (-)because it happened, spontaneous ΔH (-) because exothermic w (-) w=-PextΔV started w/ no gas, V increased exam 2v3
