Random University Chem Questions :)?

Question

Here are a few, answer what you can, all the help is appreciated
1) For a certain 1st oder rxn, the rxn goes to 38.5% completion in 480s. Calculate the rate constant for the reaction.
2)Explain the following observations:
a)The boiling point of dimethyl ether is less than that of ethanol.
b)At high densities, gases do not obey the ideal gas law
c)KF is much more soluble in water than CaO
3)Explain each of the following facts:
a)Water has a boiling point about 200 degrees greater than would be expected in comparison with the boiling points of H2S,H2Se, and H2Te
b)Water has its maximum density at 3.98 degrees celcius.
c)Methanol is soluble with water, while hexane is not.
d)Na2O is readily soluble in water, while MgO is not.
e)The freezing point of 0.1M BaCl2 is lower than that of 0.1M NaI and both are lower than that or pure water.

I know its alot, but all the help is really appreciated! Thanks in advance :)

Answer 1

1. The first order reaction is
R = Ro exp(-kt) where Ro is the initial conc of reagent, R is conc of reagent at time t, and k is the first order constant. For your data:
(R/Ro) = 0.615 = exp(- 480k)
You can grind out the math, k=0.0014 roughly.

2. Without a long-winded explanation of each
a. Ethanol, with an -OH group is more polar than ether with -O- bonding
b. The assumption of the ideal gas laws involve no interaction between molecules (or atoms) in the gas. At high pressure or low temperature, this assumption is not obeyed.
c. Group I metal ions are more easily accomodated in the water matric than a Group II metal ion.

3 a. This is due to the weak hydrogen bond attraction between the hydrogens on one molecule and the highly polar oxygen atom on a nearby molecule.
b. Water is an "ordered" liquid due to the weak hydrogen bonds discussed above. As water cools to 4 deg C, it becomes denser. Below that temperature, it is believed that small clusters of "ice", where the water molecules are lining up as if they were in a crystal, form. Since the "ice" is lighter than water, their presence overcomes the tendency for the water to continue becoming more dense.
c. CH3OH is similar enough to water so that there is appreciable weak-H bonding. Hexane is non-polar,so it doesn't disperse in the polar water to become a solution to an appreciable extent.
d. See 2(c)
e. 0.1 molar BaCl2 forms 3 ions while 0.1 molar NaCl only forms 2. Freezing point depression is a collagitive property, depending on the number of ions.

Answer 2

2)
A) no hydrogen bonding in dimethyl ether
B) molecules take up more space and are not point masses.
C) KF dissociates in H2O

3)
a)hydrogen bonding
b) bending and stretching of the molecule. as water freezes the molecule stretches. As it heats up it expands because the molecules get further apart..
c) Methanol has an hydroxl group (OH) that can take part in hydrogen bonding,
d) it dissociates.
E) molality.

I don't have enought time to do the rest. Do your own homework.

Answer 3

they are going to look at your overall grade undemanding (in a % sort). the element is, they'll require you have a definite grade in some training to be admitted. In BC, you pick a C+ or extra suitable in Math 11 to attend the college of British Columbia or Simon Fraser college (the two greatest).