Unit 2 Exam (Fall 2017) Seat # Name Lab Section: M Tu W Th MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. (3.5 pts ea) 1) In a covalent compound the bond length can be defined as A) the distance between two nuclei when the attraction is greatest. B) the distance between any two pairs of electrons. C) the distance between the two largest atoms. D) the distance between two nuclei when the repulsion is greatest. E) the distance between two nuclei when repulsion and attraction are balanced. 2) Which group contains only elements which normally exist as diatomic molecules? A) hydrogen, lithium, sodium B) helium, neon, argon C) nitrogen, sulfur, bromine D) nitrogen, oxygen, fluorine E) oxygen, phosphorus, germanium 3) In forming covalent bonds where the octet rule is obeyed, sulfur usually forms bonds and chlorine usually forms bonds. A) six; seven B) one; one C) one; two D) two; two E) two; one 4) A molecule in which the central atom has one lone pair of electrons and forms three single bonds is said to have a molecular geometry. A) pyramidal B) bent C) linear D) planar E) tetrahedral 5) Elements in Period 3 or below don't always "obey" the octet rule because they A) can use s, p, and d orbitals for bonding. B) can only use p orbitals for bonding. C) cannot use d orbitals for bonding. D) cannot use s orbitals for bonding. E) can use s and p orbitals for bonding. 6) Which element listed is the most electronegative? A) hydrogen B) chlorine C) oxygen D) fluorine E) nitrogen 7) The oxidation number of sulfur in calcium sulfate, CaSO4, is. A) +2 B) +6 C) -2 D) +4 E) 0 8) Which statement regarding balanced chemical equations is NOT true? A) The number of each kind of atoms must be the same on each side. B) Subscripts may be changed to make an equation simpler to balance. C) Coefficients are used in front of formulas to balance the equation. D) Reactants are written to the left of the arrow. E) When no coefficient is written in front of a formula, the number "one" is assumed. A-1
9) When the reaction below is correctly balanced, the sum of the coefficients, including coefficients of 1, is: C2H6(g) + O2(g) CO 2(g) + H2O(g) A) 12 B) 19 C) 17 D) 15 E) 13 10) When the reaction shown is balanced, there are atoms of oxygen and atoms of hydrogen on each side (NH4)2SO4 (aq) + Ba(C2H3O2)2 (aq) BaSO4 (s) + NH4C2H3O2 (aq) A) 4; 7 B) 8; 14 C) 16; 18 D) 6; 11 E) 16; 28 11) Which statement concerning the mole is NOT correct? A) A mole of metal contains NA atoms of that metal. B) A mole of a diatomic element contains 2 NA moles of atoms of the element. C) The molar mass of any compound is equal to its molecular weight in grams. D) A mole of any compound contains one mole of each kind of atom found in that compound. E) All of these statements are correct. 12) The formula weight of Al2(SO4)3 is g/mol. A) 450.1 B) 214.1 C) 278.0 D) 342.2 E) 315.1 13) Which sample contains the largest number of atoms? A) 2.5 mol Au B) 1.5 mol NaCl C) 3.0 mol Cl2 D) 1.0 mol H2O E) 2.0 mol CH4 14) 2 AgNO3(aq) + K2SO4(aq) 2 KNO3(aq) + Ag2SO4(s) The spectator ions in the reaction shown are A) potassium ion and sulfate ion. B) silver ion and nitrate ion. C) potassium ion and nitrate ion. D) hydrogen ion and hydroxide ion. E) silver ion and sulfate ion. 15) The value of H for the following reaction is -91kJ. 2 KClO3(s) 2 KCl(s) + 3 O2(g) When is the reaction spontaneous? A) At all temperatures B) At low temperatures C) Never D) At high temperatures A-2
16) The percentage yield of a reaction can best be described as the times 100%. A) amount of reactants left over divided by the original amounts B) total amount of materials involved in a reaction C) amount of product you could make if the reaction went to completion D) amount of desired product divided by the amount of unwanted product E) amount of product obtained divided by the calculated possible amount of product 17) How many molecules are present in 4.25 mol of CCl4? A) 2.56 1024 B) 653.69 C) 3.94 1026 D) 36.91 E) 153.81 18) The number of grams in 0.350 mol of Na is. A) 8.05 B) 65.7 C) 11.0 D) 0.350 E) 23.0 19) The combination of ions least likely to produce a precipitate is A) Pb+ and Cl-. B) Ba2+ and SO4 2-. C) Ca2+ and PO4 3-. D) Mg2+ and C2H3O2 -. E) Fe3+ and OH-. 20) A process or reaction which uses up heat from the surroundings is said to be A) endothermic. B) exothermic. C) isothermal. D) conservative. E) endergonic. 21) The concentration of reactants and products for a reversible reaction were measured at equilibrium and the value of the equilibrium constant was calculated. The calculated value of Kc=1.8x10-7. The equilibrium mixture is composed of: A) mosltly products B) mostly reactants C) a mixture of reactants and products D) more information is required to decide. 22) Fe(s) + CuCl2(aq) Cu(s) + FeCl2(aq) In the redox reaction shown, is oxidized and becomes. A) Fe, Fe2+ B) Cu, Cu2+ C) Fe, Fe+ D) Cu2+, Cu E) none of the above A-3
23) A reaction that is spontaneous can be described as A) proceeding in both the forward and reverse directions. B) proceeding without external influence once it has begun. C) having the same rate in both the forward and reverse directions. D) increasing in disorder. E) releasing heat to the surroundings. 24) N2 + O2 2 NO ΔH = 43.2 kcal Based on the reaction shown, which statement is true? A) 43.2 kcal are consumed when 1.00 g of NO is produced. B) 43.2 kcal are consumed when 1.00 mole of O2 reacts. C) 43.2 kcal are consumed when 1.00 mole of NO is produced. D) 43.2 kcal are consumed when 1.00 g of O2 reacts. E) 43.2 kcal are consumed when 1.00 g of N2 reacts. 25) Reaction rates are determined by all of the following factors except A) the orientation of collisions between molecules. B) the force of collisions between molecules. C) the activation energy of the reaction. D) the spontaneity of the reaction. E) the number of collisions between molecules. 26) Determine the number of moles of water produced when one mole of NH3 reacts according to the balanced reaction shown. 4 NH3 + 5 O2 4 NO + 6 H 2O A) 1.50 B) 0.67 C) 1.25 D) 1.33 E) 1.00 27) Which statement best describes the way a catalyst works? A) It increases the value of ΔG. B) It increases the value of ΔH. C) It increases the value of Eact. D) It decreases the value of ΔH. E) It decreases the value of Eact. 28) Consider the reaction: A(g) + 2 B(g) 2 C(g) + D(g) The equilibrium expression for this reaction is A) 2[C][D] B) [A][B] 2 [A]2[B] [C]2[D] C) [A]2[B] 2 2[C]2[D] D) [A]2[B] 2[C][D] E) [C] 2[D] [A][B]2 A-4
29) Consider the reaction shown: N2 + O2 2 NO ΔH = 43.2 kcal When 50.0 g of N2 react, kcal will be. A) 77.1; produced B) 77.1; consumed C) 2160; produced D) 2160; consumed E) 43.2; produced 30) Determine ΔG rxn using the following information. H2(g) + CO(g) CH2O(g) ΔH = +1.9 kj; ΔS = -109.6 J/K A) -41.5 kj B) +57.7 kj C) +34.6 kj D) +17.3 kj E) -30.8 kj TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. (3 pts ea) 31) All exergonic reactions are spontaneous. 32) Adding a catalyst will increase G. 33) Increasing the concentation of reactants will increase the rate of reaction because the collisions become more forceful. 34) All single replacement reactions are redox reactions. 35) The electron pair geometry for an atom with a lone pair, a single bond, and a double bond is bent. 36) Based on the following reaction happening, Fe is more active than Cu. Fe(s) + CuCl2(aq) Cu(s) + FeCl2(aq) A-5
SHORT ANSWER. Circle the appropriate word, fill in the blank, or work out the problem. The following questions are worth 2 pts each. 37) What is the formula for chromium (III) sulfate? 38) What is the formula for calcium nitrate? 39) What is the name for K 2 O? 40) What is the name for Cu(C2H3O2)2 41) What is the name for H3PO4(aq) 42) What is the name for SiCl4 43) Write the equilibrium constant expression for the following reaction: (3 pts) 2 NaCO3(s) + 2 SO2(g) + O2(g) 2 NaSO4(s) + 2 CO2(g) Kc= 44) Determine the molecular formula and the number of lone pairs of electrons for the the compound (caffeine) with the following line-bond structure. (4 pts) molecular formula number of lone pairs 45) Determine the molecular geometry around the indicated atoms in the following molecule: (6 pts) a) b) c) d) A-6
46) Draw the expanded structure for the compound with the following condensed structure. CH3CH2COCH(CH3)2. (3pts) 47) Consider the covalent compound SO3. a) Draw the Lewis dot structure for the molecule. (2 pts) b) Determine the moleular geometry of the molecule. (2pts) c) Draw an appropriate diagram that indicates the shape. Identify on the diagram any polar bond and the direction of the polaity with arrows. (2 pts) d) Identify if the overall molecule is polar or nonpolar. (1 pt) e) If polar, draw the direction of the dipole moment. If nonpolar, explain why. (1 pt) Note: electronegativity of sulfur is 2.5 and electronegativity of oxygen is 3.5. Circle the appropriate word or fill in the blank. 48) (4pts) Consider the reaction shown: Cl2 + H2C=CH2 ClCH 2CH2Cl + 52 kcal We can say that this reaction is [exothermic/endothermic] and that the sign of ΔH is [positive/negative]. 49) (4pts) 2 Al2O3 (s) 4 Al (s) + 3 O2 (g) ΔG = +138 kcal Consider the contribution of entropy to the spontaneity of this reaction. As written, the reaction is [spontaneous/non-spontaneous], and the entropy of the system [increases/decreases]. 50) (4pts) The carbon dioxide molecule is linear. The electronegativities of C and O are 2.5 and 3.5, respectively. Based on these values and on consideration of molecular geometry, the C-O bond is [polar/non-polar] and the molecule is [polar/nonpolar]. 51) (4pts) In a double replacement reaction between solutions of potassium sulfate and barium chloride, the formulas (not names)for the products would be and. (Include proper state symbols. (1/2 pt ea) A-7
52) (3pts) For the reaction 2 Al2O3 (s) 4 Al (s) + 3 O2 (g) The total number of electrons transfered is. 53) According to LeChatlier's Prnciple, C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O (l) DH =- 488 kcal Which way would the previous equilibrium shift (left or right) if: a) (2pts) If the container in which the above reaction took place were placed in an ice bath. b)(2pts) If the pressure was increased by reducing the size of the container. c) (2pts) If carbon dioxide was added to the container. 54) Consider the reaction N2 (g) + O2 (g) 2 NO (g). a. How many moles of NO can be produced when 25.0 g of nitrogen reacts? (2 pts) b. How many moles of NO can be produced when 25.0 g of oxygen reacts? (2 pts) c. Based on your answers in a and b, predict the amount (in grams) of NO that can be produced when 25.0 g nitrogen is reacted with 25.0 g of oxygen. (2 pts) a) b) c) A-8
55) Consider the reaction: 2 SO2 (g) + O2 (g) 2 SO3 (g) What is the concentration of oxygen gas if the value for the equilibrium constant, Kc, is 2.80 x 102 and the equilibrium concentrations of the other constituents are: [SO2]=0.075 mol/l and [SO3]=0.925 mol/l. Show your work. (4pts) 56) How many grams of CO2 will be produced when 5.00 grams of Na2SO4 react according to the unbalanced reaction shown? Show all work, and include appropriate units with dimensional analysis to get full credit.(6pts) Na2SO4 + C Na2S + CO2 The following Extra Credit problem is worth 7 points. 57) Write the balanced Total, Ionic, and Net Ionic Equations for the reaction that occurs when solutions of nickel(ii) nitrate and lithium phosphate are mixed. Total Ionic NIE Driving Force: A-9