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Chapters 11 and 12

100

If ΔH = +100 kJ for a reaction, then the reaction is

Endothermic

200

What is the length of one side of the body–centered cubic tungsten unit cell given that the density of tungsten is 19.35 g/cm3 and that its atomic radius is 135 pm?

312 pm

300

Consider the following reaction: 2NaH(s)--> 2Na(s) + H2(g) The enthalpy change for this reaction at standard temperature and pressure is

– 2(delta)Hf˚ (NaH(s))

400

When 5.00 g of ammonium nitrate are dissolved in 1.00 L of water in a calorimeter with a heat capacity of 2.30 kJ•K–1, the temperature drops 0.760 K. What is the molar enthalpy of solution of ammonium nitrate? [ M(NH4NO3) = 80 g/mol ]

+28.0 kJ•mol–1

500

For a certain reaction at constant pressure, (delta)U = –125 kJ and 22 kJ of expansion work is done on the system. What is (delta) H for this process?

–147 kJ

Chapter 13

100

What is the expected osmotic pressure (in atm) of a 0.0530 M MgCl2 solution at 25˚C?

π=iMRT =(3.00 mol ions/1 mol MgCl2)(0.0530 mol MgCl2/1L soln) (0.08206 Latm/mol K) (298 K)= 3.9 atm

200

The vapor pressures of pure benzene and pure toluene at 25◦C are 95.1 and 28.4mmHg, respectively. A solution is prepared in which the mole fractions of benzene and toluene are both 0.500. What are the partial pressures of the benzene and toluene above this solution?

Use Raoult’s Law P (benzene) = x(benzene)*P(pure benzene) = 0.500 * 95.1 mmHg = 47.6 mmHg P(toluene) = x (toluene)* P(pure toluene) = 0.500 * 28.4mmHg = 14.2mmHg

300

An aqueous solution is 0.0222 m glucose. What are the boiling and freezing point of this solution? Kb=0.512 degrees Celsius/m and Kf=1.86 degrees Celsius/m.

(delta)Tb=Kb*cm=0.512*0.0222=0.0114 degrees Celsius (delta)Tf=Kf*cf=1.86*0.0222=0.0413 degrees Celsius.

400

What are the mole fractions of glucose and water in a solution containing 5.67 g of glucose, C6H12O6, dissolved in 25.2 g of water? MW of H2O=18 g/mol. MW of glucose= 180.2 g/mol

0.0220 mole fraction of glucose and 0.978 mole fraction of water.

500

What state am I from?

Mississippi

Chapters 15 and 16

100

For the reaction NO (g) +1/2 O2 (g)--> NO2 (g) at 184˚C, K= 7.5*10^2. What is the value at 184˚C for the reaction 2NO2 (g)--> 2NO (g) + O2 (g)?

NO2 (g)--><-- NO (g) + ½ O2 (g) Kc= 1/ (7.5*10^2)= 0.0013 2NO2 (g) --><-- 2 NO (g) + O2 (g) Kc= (0.0013)2=1.7*10^-6

200

A 0.0025M solution of HI (aq) has [H3O+] = 0.0025M. Calculate the [I-], [OH-], and the pH of the solution.

pH is determined from [H30+], pH = -log [H3O=] = -log (.0025) = 2.60 We know that HI is a strong acid and this completely dissociated into H3O+ and I-. The consequence is that [I-] = [H3O+] = 0.0025M. [OH-] is most readily computed from pH: pOH=14-pH= 14-2.60= 11.40 --> [OH-] = 10^(-pOH) =4.0E-12

300

A solution has a pH of 2.85, what are the [H+] and [OH-]?

Calculate [H+] from [H+] = 10^-pH Then pOH= 14 – pH = 14 – 2.85 = 11.15. Therefore, [OH-] = 10^-pOH = 7.1 E-12 [H+] = 1.4 E-3 [OH-] = 7.1 E -12

400

Calculate the pH of an aqueous HNO3 solution that has a volume of 250mL and contains 0.4649g HNO3. MW= 63.012 g/mol)

Nitric acid is a strong acid, so every mole of HNO3 that dissolves produces a mole of H3O+ and a mole of NO3-. Determine the number of moles of HNO3 and then calculate the H3O+ concentration. 0.465g HNO3 * (1mol/63.012g HNO3) = 0.007380 mol HNO3 [H3O+] = (0.0073820 mol HNO3)/.250 L = 0.0295 M pH = -log(.0295) = 1.530

500

A 5.00 L evacuated flask is filled with 1.86 mol NOBr. At equilibrium at 25˚C, there is 0.082 mol of Br2 present. Determine Kc and Kp for the reaction 2NOBr (g)-- > < -- 2NO (g) +Br2(g).

2NOBr (g)-- > < -- 2NO (g) + Br2(g) initial 1.86 mol 0 mol 0 mol change -2x +2x +x equilibrium1.86-.164= 1.70mol .164mol .082 mol Kc= (1.64mol/5.00L)2 (.082 mol/5.00 L)/ (1.70 mol/5.00 L)2= 1.54*10^-4 Kp= (1.54*10^-4)(.08206*298)=3.7*10 ^-3

Chapter 17

100

Calculate [H3O+] and [CHO2-] in a solution that is 0.100M HCHO2 and 0.150M NaCHO2. Ka=1.8*10^-4

[H3O+] = 1.2E-4 [CHO2-] = 0.150M + .00012M = 0.150M

200

Determine the pH of a Buffer from Ka: You have prepared a 1.0L solution of buffer containing 0.0025mol carbonic acid and 0.025 mol hydrogen carbonate ion. Calculate the pH of the buffer. Ka = 4.2 x 10^-7

Henderson Hasselbach: pH=pKa+log[A-]/[HA] 7.38

300

Calculate the pH of a buffer containing 0.090 mol/L pyruvic acid (CH3COCOOH) and 0.130 mol/L of sodium pyruvate, Na+CH3COCOO-. Given: Ka of pyruvic acid: 3.2 x 10^-3

pH= 2.65

400

If I had a solution with a H3O^+ of .0056 M, what would be the OH concentration?

1.79*10^-12

500

Daily Double: What school (and location) did I attend for undergrad?

Howard University, Washington, DC

Chapter 18 and 19

100

How could you mathematically determine if a reaction will form a precipitate or not?

Calculate the reaction quotient, Q, and determine if Q is greater than, less than, or equal to K.

200

Write the solubility product expressions for the following salts: a.) Hg2Cl2 b.) Pb3(AsO4)2

Hg2Cl2(s)--><--Hg2^2+ (aq)+ 2Cl^-(aq); Ksp=[Hg2^2+][Cl-]^2 Pb3(AsO4)2--><--3Pb^2+ (aq)+ 2AsO4^3- (aq); Ksp= [Pb^2+]^3[AsO4^3-]^2

300

The solubility of silver bromate, AgBrO3, in water is 0.0072 g/L. Calculate Ksp. Molecular weight=235.77

9.3*10^-10

400

Find the value of the equilibrium constant K at 25˚C (298 K) for the reaction 2NH3 (g)+ CO2 (g)--><-- NH2CONH2 (aq) +H2O (L) The standard free-energy change, ΔG˚, at 25˚C equals -13.6 kJ.

2.4*10^2

500

For the ammonia synthesis reaction at 25˚C, calculate the change in Gibbs free energy if 1 mol N2 (g) at 0.23 bar and 3 mol H2(g) at 0.42 bar is converted to 2 mol NH3 (g) at 1.45 bar. Given: (delta)G(N2(g))=0, (delta)G(H2(g))=0, (delta)G(NH3(g))=-16.45 kJ/mol

-20.96 kJ/mol