NESA Chemistry Problem Solving

Carbon
$n(C) = n(CO_2) = 1.320/44.01 = 0.02999$ mol
$m(C) = 0.02299 \times 12.01 = 0.3602$ g

Chlorine
$n(Cl) = n(HCl) = n(NH_3) = 1.050 \times 0.08570 = 0.08999$ mol
$m(Cl) = 0.08999 \times 35.45 = 3.1900$ g

Fluorine
$m(F) = 4.121 - (0.3602 + 3.1900) = 0.5708$ g
$n(F) = 0.5708 / 19.00 = 0.03004$ mol

Mole Ratio
C: 0.02999
Cl: 0.08999
F: 0.03004

Simplify
Divide by 0.02999
C: 1
Cl: 3.00
F: 1.002

Empirical Formula
$CCl_3F$

Molecular Formula
Empirical formula mass (EFM) = 137.36 amu/g mol$^{-1}$
$n = PV/RT = (120.0 \times 0.6068)/(8.314 \times 323.75) = 0.027052476$ mol
Molecular formula mass (MFM) = $m/n = 3.721/0.0276503204 = 137.54$ g mol$^{-1}$
Molecular formula = MFM/EFM $\times$ Empirical formula = $137.54/137.36 \times CCl_3F = 1.0013 \times CCl_3F$

Molecular formula = Empirical formula = $CCl_3F$

2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(l) or
CH4(g) + 1.5O2(g) → CO(g) + 2H2O(l)

$n(\text{CH}_4) = 20.0 / 16.0 = 1.25 \text{ mol} *$
$\text{Pressure}(\text{CH}_4) = nRT / V = 1.25 \times 8.31 \times 298 / 5.0 = 6.2 \times 10^2 \text{ kPa} *$

$\text{Energy from CH}_4 = 0.485 \text{ g} \times 55.6 \text{ kJ g}^{-1} = 27.0 \text{ kJ}$

$\text{Energy absorbed by water} = 4.18 \text{ J g}^{-1} \text{ K}^{-1} \times 350.0 \times (32.3 - 20.0)$
$= 1.80 \times 10^4 \text{ J}$
$= 18.0 \text{ kJ}$

$\text{Energy lost to environment} = 27.0 - 18.0 = 9.0 \text{ kJ}$

$\% \text{ energy lost} = (9.0 / 27.0) \times 100 = 33.3 \%$

Similarity – methane from both sources

• Both produce atmospheric carbon dioxide through combustion.
• Methane from both sources contains small amounts of nitrogen and sulfur; combustion of natural gas leads to the formation of acidic oxides such as SOx and NOx.

Difference – landfill versus natural gas

• Methane from landfill can be produced renewably, whereas methane from natural gas releases stored carbon.
• Methane from landfill is more carbon neutral, methane from natural gas increases atmospheric CO2 levels.
• Obtaining methane from natural gas via fracking causes additional significant environmental damage, whereas when obtaining methane from a landfill the damage has already been done in the formation of the landfill.
• Landfill gases contain less methane and release more CO2 (for the same amount of energy generated), natural gas contains more methane and releases comparatively less CO2.
• Methane captured from landfill and used as a source on energy may have a positive impact as it is a more potent greenhouse gas than CO2.
• CH4 from landfill is more easily collected compared to fracking/sourcing methane from fossil fuels.