Problem: The methane molecule, CH4, has the geometry shown in following figure. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four C–H bonds to infinity. We then have the process CH4(g) → C(g) + 4 H(g).Suppose that 3.45 g CH4(g) reacts with 1.22 g F2(g), forming CF4(g) and HF(g) as sole products. If the reaction occurs at constant pressure, what amount of heat is evolved?

FREE Expert Solution

Balanced reaction: CH4(g) + 4 F2(g) → CF4(g) + 4 HF(g)

ΔH°rxn=ΔH°f, prod-ΔH°f, react

ΔH°rxn=(1 mol CF4)-933.6 kJ1 mol CF4+(4 mol HF)(-273.3 J1 mol HF)           -(1 mol CH4)-74.6 kJ1 mol CH4+0

ΔH˚rxn = –1952.2 kJ/mol


Find the limiting reactant:

HF from CH4:

molar mass CH4 = 16.042 g/mol

moles HF=3.45 g CH4×1 mol CH416.042 g CH4×4 mol HF1 mol CH4

moles HF = 0.860 mol HF


HF from F2:

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Problem Details
The methane molecule, CH4, has the geometry shown in following figure. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four C–H bonds to infinity. We then have the process CH4(g) → C(g) + 4 H(g).

The figure shows a ball-and-stick model and a perspective drawing of CH4.

Suppose that 3.45 g CH4(g) reacts with 1.22 g F2(g), forming CF4(g) and HF(g) as sole products. If the reaction occurs at constant pressure, what amount of heat is evolved?

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