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### At the end of $2012,$ global population was about…

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Manhattan College

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Problem 96

It is interesting to compare the "fuel value" of a hydro- carbon in a hypothetical world where oxygen is not the combustion agent. The enthalpy of formation of $\mathrm{CF}_{4}(g)$ is $-679.9 \mathrm{kJ} / \mathrm{mol} .$ Which of the following two reactions is the more exothermic?
$$\begin{array}{l}{\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)} \\ {\mathrm{CH}_{4}(g)+4 \mathrm{F}_{2}(g) \longrightarrow \mathrm{CF}_{4}(g)+4 \mathrm{HF}(g)}\end{array}$$

The reaction with fluorine as the combustion agent is almost twice as exothermic as the reaction with oxygen.

## Discussion

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## Video Transcript

All right, So this is problem ninety six of twenty five in chemistry. The central science. They want to know which of these two reactions is more esoteric. So we're going to use Hess's law. Oh, to figure out which is more, more ex atomic number has his law reaction is equal. Delta agent the product money sell th of the reactors since. So there's going to be the first equation agent two times. They're two orders to forty one point two two plus two so minus three ninety three point five minus. There's thie. It is minus native, said the four point eight. Remember, we don't need the the number for the Day of the age for information for F to know, too, are zero, because that's an element into standard state Great eight. So we have. So this one is going to be negative. Eight point two dory for killing joules per mall. Half of the bottom one, four times Positive Negative. Two sixty eight with sixty one on minus and it's six seventy nine Fine. Yeah, point nine, Master. Minus this, they get seventy four point eight and this is going to be minus sixteen. Seventy nine nine point five four kilograms per mole. So that means that the interaction of methane with with floor with Diana flooring is actually more except thermic. Then then then the combustion of men. Methe name of oxygen unction with flooring producing negative of sixteen seventy nine. Well, option producing minus eight. Oh two. This is most likely due to the fact that when floor that CF four is going to be more stable is going to be more stable than us. See, then go to because the bonding is stronger. Flooring is more Electra negative than oxygen after Jin. So you're goingto have a lower energy in your bond, so you're bonding is going to be lower energy.