Chapter 11 Exam 2 Content
For 38.0 grams of water at 2 C at sea level pressure, how much heat energy (q) is needed to turn this into 38.0 grams of water at 120 C at sea level pressure (pressure is constant)? Delta H vap H2O = 40.7 kJ/mol, MW H2O = 18.00 g/mol
Work through with class
qtot = qheating1 + qvap + qheating2
Consider the following balanced reaction:
2C2H6(g) + 7O2(g) -> 4CO2(g) + 6H2O(g)
Will DeltaS be positive or negative
Positive, b/c
#moles of gas products < #moles of gas reactants
What is the mass percent of 12 grams of ethanol dissolved in 250 grams of water?
(12/(12+250))*100%
What is the vant hoff factor for Glucose?
1, because it is a non electrolyte
When is q = n*DeltaH used instead of q = m*Cs*DeltaT?
When a phase change occurs
Consider the following reaction:
Cu(s) + H2SO4(aq) -> CuSO4(aq) + H2(g)
Will the product side solution form?
Yes, b/c the DeltaS of the reaction = +
What is the molarity 2 grams of acetic acid (CH3COOH), (molar mass = 60.05 g/mol) in 125 mL of it's solution (in water)?
Solve with class
(2/60.05mol)/(0.125 L)
During the winter, roads tend to get very icy in cold places of the world. In order to allow for people to continue to drive despite the inclement weather, salt is often used on the roads, which will cause the ice on the road to melt. What colligative property causes this to occur?
Freezing point depression
Consider Acetone, (CH3COCH3), which is a popular compound used in nail polish remover and is a strong organic solvent. It is a polar molecule with it's strongest IMF being DDF. Would you expect it to vaporize faster than water under standard atmospheric pressure and room temperature? Why or Why not?
You would expect it to vaporize readily under these conditions at least when compared to water, since it has a higher volatility and vapor pressure than water due to having weaker IMF.
Consider Cyclohexane, a cyclic alkane with the formula C6H6. Will it form a solution with Sodium Chloride (NaCl) at room temperature? Why or why not?
No because the DeltaH of the solution cannot overcome the DeltaH of the solute.
What mole fraction does 2 grams of H2 have in a container containing 2g H2, 5g Ne, & 10 g CH4?
1. Get MM of all components and solve for n
2. Set up equation (n H2)/((n H2) + (n Ne) + (n CH4))
Find the boiling point elevation attained from mixing 12 g of Calcium Nitrate in 240 g of water. Kb water = 0.512 C*kg/mol
Bp Water = 100C
Vant Hoff Factor = 3
Molar Mass: 1(40.08)+1(14.01)+3(16.00) = 102.09 g/mol
kg water = 0.240 kg
Delta T = ((12/102.09)/0.240)mol/kg*3*0.512 C*kg/mol
New Bp = 100 C + Delta T (C)
In nature, some bacteria are resilient against the standard temperature at which water boils (100C). Therefore a device known as an autoclave is often used to completely sanitize equipment used in the medical fields. The autoclave is able to achieve higher temperatures in boiling water by raising the pressure inside to well above standard atmospheric pressure. Based off of what you have learned, why does this work?
Because when pressure is raised, boiling points of fluids tend to raise with it as well.
Solve w/class, cross multiplication used to solve
How many ppm does an aqueous solution at room temperature containing 54 mg/mL of CO2 have?
Solve with class,
d = 1.0 g/mL
54 mg/mL = 54mg CO2 / 1 g H2O
(54mg/1g)*(1g/1000mg)*(106/106)
Consider a cell with a NaCl concentration of 0.1 M inside the cell. The environment outside the cell however has a NaCl concentration of 0.01 M. Assuming no action is taken by the cell to control the concentration inside the cell, is the cell existing in a hypo, hyper, or isotonic environment, & what will occur as result?
The cell is in a hypotonic solution, & it will swell & lyse as result
Using the Integrated C-C equation, determine at what pressure will water boil at 40C when compared to water's boiling point at standard pressure? DeltaHvap H2O = 40.7 kJ/mol
Work through w/class, but
ln(P2/P1) = (DeltaH/R)*((1/T1-(1/T2))
e^((DeltaH/R)*((1/T1)-(1/T2))) = P2/P1
Solve from here (may vary depending on how you assembled the equation)
What is the pressure of ammonia gas in a solution inside a closed container, where ammonia's concentration in the solution is 1.2 M? Ammonia's Henry Law Constant = 59 M/atm
Solve with class,
S = PK
What is the molarity of a solution containing 17 g of KNO3 in 250 g of water? MM KNO3 = 101.11 g/mol
Molarity cannot be determined here if density is not known, however if it was known (i.e. at room temperature, where d = 1.0g/ml), and the density of the solution roughly equals that of the solvent, it can be solved as such:
(17/101.11)mol/(0.250 L)
Find the concentration in Molar of Glucose with an osmotic pressure of 0.7 atm and at 30 C? (R = 0.08206 L*atm/mol*K
Solve alongside class
M = pi/(RT)
i = 1
30 + 273 = T in K