ap chem nti ii key - jessamine.k12.ky.us

APChemNTIIIKEYCurrently,thereisamassivenaturalgasleakattheAlisoCanyonstoragefacilityinPorterRanch,CalifornianearLosAngeles.Gasisstoredbyinjectingitdeepundergroundintodepletedgaswells.Initiallythewellwasleakingover44,000kilogramsofnaturalgasanhour!

Thestoragefacilitycontainsapproximately22billioncubicfeet(6.3x1011L)ofgas.Atthedepthwherethegasisconfinedpressuresare20atmandatemperatureof147oC.Ifthegasfacilityweretocompletelyleaktothesurface,findwhatvolumethegaswouldhaveatnormalpressuresandtemperatures(1atmand25oC).

UseCombinedGasLaw!!!!

!! = !!!!

!!

20 𝑎𝑡𝑚 ∙ 6.3 ∙ 10!!𝐿(147+ 273)𝐾 =

1 𝑎𝑡𝑚 ∙ 𝑉!25+ 273 𝐾 ∴ 𝑉! = 8.9 ∙ 10!"𝐿

Naturalgasispredominatelymethane(CH4).Methaneis25timesmorepotentasagreenhousegasthancarbondioxide.Usingthecombustionofoctaneasamodelforgasoline,findthelitersofgasolinethatwouldneedtobeburnttoproducecarbondioxideofequivalentgreenhousegaseffecttovolumeofmethanereleasedifthestoragefacilitycompletelyemptied.Use1atmand25oC.Thedensityofgasolineis770g/L.

Combustionofoctane

2 C8H18 + 25O2 ! 18 H2O + 16 CO2

Use PV = nRT to find moles of Methane

1 𝑎𝑡𝑚 ∙ 8.9 ∙ 10!"𝐿 = 𝑛 ∙ 0.0821!"#∙!!"#∙!

∙ 298𝐾 ∴ 𝑛 = 3.6 ∙ 10!!

Multiple moles of metane by 25 because 1 mole CH4 = 25 mole CO2

𝑚𝑜𝑙𝑒𝑠 𝐶𝑂! = 9.0 ∙ 10!"

Use stoichiometry to convert moles CO2 to L of gasoline (octane) 9.0 ∙ 10!" 𝑚𝑜𝑙 𝐶𝑂!

∙2 𝑚𝑜𝑙 𝐶!𝐻!"16 𝑚𝑜𝑙 𝐶𝑂!

∙114.26 𝑔1 𝑚𝑜𝑙 ∙

1 𝐿770 𝑔 = 1.7 ∙ 10!!𝐿

(Incidentally, this is enough for me to drive my car the distance to the moon and back 3,800 times!)

A 2L tank contains 10g of each of these gasses at 400oC: Methanol (CH3OH), Carbon monoxide (CO), and Hydrogen (H2). Find the total pressure in the tank. Find total moles

10𝑔 𝐶𝐻!𝑂𝐻32.05 𝑔 ∙𝑚𝑜𝑙!! +

10𝑔 𝐶𝑂28.01 𝑔 ∙𝑚𝑜𝑙!! +

10𝑔 𝐻!2.02 𝑔 ∙𝑚𝑜𝑙!! = 5.6 𝑚𝑜𝑙

Use total moles in PV = nRT 𝑃!"! ∙ 2𝐿 = 5.6𝑚𝑜𝑙 ∙ 0.0821!"#∙!

!"#∙!∙ 400+ 273 𝐾 ∴ 𝑃!"! = 160 𝑎𝑡𝑚

Find the partial pressure of each gas.

Use Law of Partial Pressures 𝑃!𝑃!"!

=𝑉!𝑉!"!

=𝑛!𝑛!"!

Methanol 𝑃!!!!"160 𝑎𝑡𝑚 =

. 31 𝑚𝑜𝑙5.6 𝑚𝑜𝑙 ∴ 𝑃!!!!" = 8.9 𝑎𝑡𝑚

Carbon Monoxide 𝑃!"

160 𝑎𝑡𝑚 =. 36 𝑚𝑜𝑙5.6 𝑚𝑜𝑙 ∴ 𝑃!! = 10.3 𝑎𝑡𝑚

Hydrogen 𝑃!!

160 𝑎𝑡𝑚 =5.0 𝑚𝑜𝑙5.6 𝑚𝑜𝑙 ∴ 𝑃!! = 140 𝑎𝑡𝑚

How do the average kinetic energies of each gas compare. Explain.

The average kinetic energies are all equal because all three gasses are at the same temperature.

How do the average molecular speeds of each gas compare. Explain.

KE = 1/2mv2, so at a given temperature, the lightest gases will be moving the fastest. Hydrogen will have the highest average velocity followed by carbon monoxide followed by methanol.

The temperature was lowered to below the boiling point of methanol. Small amounts of H2 gas and CO gas were found to be dissolved in the liquid. Which of the two gases would you expect to be more soluble in liquid methanol?

The forces between hydrogen gas and methanol would be weak London dispersion forces because hydrogen is a nonpolar molecule. The London dispersion forces between carbon monoxide and methanol would be stronger because carbon monoxide has more electrons (more polarizable). Additionally, both carbon monoxide and methanol are polar molecules so dipole-dipole interactions could form. With stronger intermolecular forces between carbon monoxide and methanol, more carbon monoxide would be expected to dissolve than hydrogen

C2H4(g) in a tank is heated from 300 to 450K and the pressure is observed to increase. Describe at the molecular level why this occurs.

Pressure is force per unit area. Force is created when gas molecules collide with the walls of a container. As the temperature increases, the average velocity of the molecules will increase. This will increase the frequencies the molecules collide with the walls of the tank. The increased average velocity will also increase the average kinetic energy of the molecules. When they strike the walls of the tank, they will do so with more force.

Once the tank is at 450K, HCl(g) is injected into the tank. This reaction occurs:

C2H4(g) + HCl(g) ! C2H5Cl(g)

The pressure on the tank initially increases, but as the reaction occurs, the pressure decreases. Describe at the molecular level why this occurs.

Initially, the additional gas molecules from the added HCl will create additional collisions and therefore more pressure in the container. However, as the reaction proceeds, 2 gas molecules are consumed (1C2H4 and 1 HCl) but only one is produced (1 C2H5Cl), which reduced the number of molecules of gas and therefore the pressure.