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CHM 1311 D
Midterm
Fall 201 7
Please keep your work covered at all times and keep your eyes on your own paper!
Cheating or any appearance of cheating will result in an F in the course and possible
expulsion from the university.
There are 8 pages in this test, for a total of 40 marks. A periodic table and data
sheets are provided at the end. You may rip these pages off of the exam and use
them to cover your work during the test. Any scratch work should be done on the
back of these pages.
Please show all work to receive partial credit.
Make sure that units are included in your final answer.
You have 90 minutes to complete the test.
Question 1. Short answer questions (1 mark each) a) A 5.00 L flask is filled with argon gas at 1.35 atm and 31.0 oC. After a 3.00 mol sample of nitrogen gas is added at this temperature, what is the partial pressure of argon? b) Are the bond energies used to estimate reaction energies exothermic or endothermic? c) At constant pressure an ideal gas inside a piston contracted, involving 250 J of work and releasing 500 J of heat. What is the value of ΔE for the gas in this process? d) A micropipette can remove 1 mL of liquid from a solution to an accuracy of 1 μL. How many significant figures should you use to record the volume of the aliquot of solution removed by this pipette? e) Write the chemical symbol for the element containing 13 protons, 10 electrons and 14 neutrons. f) If the standard heat of formation of liquid H 2 O is - 285 kJ mol-^1 , then what will be the heat of the reverse reaction performed with 0.50 mol of liquid H 2 O? Question 2. Short calculations a) What is the root mean squared speed of an oxygen (O 2 ) molecule at 298 K? (2 marks)
f) What would the concentration of potassium be if a 35.0 mL sample of 0.025 M K 2 SO 4 was added to 50.0 mL of 0.50 M K 3 PO 4? (3 marks) Question 3. A customer to a pawn shop wants to sell a ring weighing 13.8 g. To determine the composition of the ring the pawn shop owner places it into a pot of boiling water. The hot is then transferred to a coffee cup calorimeter containing 25.0 mL of room temperature (25.0oC) water. Using the data in the table below, determine what this ring made out of, given that the temperature of the water in the calorimeter rose to 26. o C? (4 marks) Specific heat capacities (J g
- 1 o C - 1 ) liquid water 4. gold 0. brass 0. stainless steel 0.
Question 4. Answer the questions below. You may need to use data provided on the equation sheet. a) Calculate the standard combustion enthalpy for liquid butanol. (3 marks) b) Calculate Δ E R^ o e^ action for the standard combustion of liquid butanol. (3 marks) Question 5. Hydrogen gas, H 2 (g) is passed over Fe 2 O 3 (s) at 400oC. Water vapour is formed together with an iron oxide containing 72.3% Fe by mass. What is the empirical formula of this iron oxide? (4 marks)
Constants and Conversion Factors 1 mmHg = 1 torr 760 mmHg = 1 atm 1 atm = 101.325 kPa 1 atm = 1.013125 bar 1 bar = 10 5 Pa 1 cm 3 = 1 mL = 1000 μL 1 dm 3 = 1000 mL = 1 L 1 m 3 = 1000 L 1 cal = 4.184 J 1 L = 1000 mL 1 m = 100 cm 1 m = 10^12 pm Avogadro’s Number NA 6.022x10^23 mol-^1 Gas constant R 8.31451 J·K
- 1 ·mol - 1 R 0.08206 atm·L·K
- 1 ·mol
- 1 R 8.31451 L·kPa·K
- 1 ·mol
- 1 R 0.0831451 bar L·K-^1 ·mol-^1
Data
Δ H of^ (C 4 H 10 O (^) ( l )) = − 327. 0 kJ mol-^1 Δ H of^ ( H 2 O (^) ( l )) = − 285. 83 kJ mol-^1 Δ H of^ (C O 2 ( g )) = − 393. 5 kJ mol-^1 Δ H (^) f o (H 2 O^ ( g^ )) =^ −^241.^8 kJ^ mol
Equations
T (^) (i n K) = T (^) (i n oC) + 273. 15 K n = m M
N
NA
% Yield = actual yield theoretical yield c (^) (m ol / L) = n V c 1 V 1 = c 2 V 2 = n p = mg A p = dgh pV = nRT p 1 V 1 T 1
p 2 V 2 T 2 pT = p 1 + p 2 + p 3 + … pA = X (^) A × pT X (^) A = nA nT d = m V
p ⋅ M RT
EK =
m v^2 E =
3 RT
2 N A
v =
3 RT
M
Rate A Rate B
M B
M A
p = nRT (^ V^ −^ nb ) − a n 2 V^2 Δ E = w + q w = F × d = − p Δ V q calorimeter = Ccal Δ T Δ E reaction = Σ BE reactant bonds broken − Σ BE product bonds formed Δ E molar =
Δ E
n Δ H r^ o e^ action= Σ vp Δ H of ,^ p − Σ vr Δ H of , r Δ H reaction = Δ E reaction + RT Δ ngas H = E + pV
