1. The thermal decomposition of potassium chlorate can be used to produce oxygen

Question

1. The thermal decomposition of potassium chlorate can be used to produce oxygen in the laboratory: 2 KClO3(s) → 2 KCl(s) + 3 O2(g). What vollume (in L) of O2 gas is produced by the decomposition of 7.5g of KClO3(s) at a temperature of 25 °C and a pressure of 1atm?

2. Which of teh following gases would have the highest average molecular speed at 25 °C?
(a) O2
(b) N2
(c) CO2
(d) CH4
(e) SF6

3. What is the freezing point of a solution prepared by dissolving 11.3g of Ca(NO3)2 in 115g of water? (The molal freezing point depression of constant water is 1.86 °C/m).

4. Both of the molecules n-Pentane and Neopentane have the same molecular formula (C5H12), but n-Pentane has a higher boiling point. Which statement below best describes why n-Pentane has the higher boiling point?
(a) n-Pentane exhibits hydrogen bonding.
(b) Neopentane exhibits hydrogen bonding.
(c) The flatter shape of n-Pentane allows for greater intermolecular contact.
(d) Neopentane molecules have stronger dipole moments than n-Pentane molecules.
(e) London Dispersion Forces on Neopentane are greater than on n-Pentane.

Explanation / Answer

1st part answer is 2.2 L.

2. The average speed of gas molecules depends on the molar mass.

avg speed = SQRT(3RT/M)
where
avg speed is the RMS average speed
SQRT means square root of...
R is the gas constant in J/molK
T is the absolute temperature
M is the molar mass

As you can see, the average speed is inversely proportional to the molar mass. The heavier the molecule, the slower it moves, on average.

Therefore, find the molar mass of the gases in question, the heaviest one (the one with the greatest molar mass) will move the slowest, and the lightest one will have the highest average speed.

So N2 with molecular mass 14 will move faster. so correct is N2

3.
moles Ca(NO3)2 = 11.3 / 164 = 0.0689
i = 3
delta T = 3 x 0.0689 x 1.86 = 0.384
f.p. = - 0.384 ÂÂ °C

4.because n-pentane is a straight chain hydrocarbon meaning it has more surface area to reach the boiling point, neopentane has significantly less surface area thats why it will boil quicker than n-pentane. keep in mind the more branched a molecule is the lower its boiling point will be and the less branched a molecule is the higher its boiling point will be. For combustion energy the opposite holds true, the more branched molecule has a higher energy than an unbranched one!

so correct answer is C)

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