### Use standard free energies of formation to calcul…

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Problem 62

For each reaction, calculate $\Delta H_{\mathrm{rxn}}^{\mathrm{o}}, \Delta S_{\mathrm{rm}}^{\circ}$ and $\Delta G_{\mathrm{rxn}}^{\circ}$ at $25^{\circ} \mathrm{C}$ and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from $25^{\circ} \mathrm{C} ?$
\begin{equation}\begin{array}{l}{\text { a. } 2 \mathrm\ {CH}_{4}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2}(g)} \\ {\text { b. } 2 \mathrm\ {NH}_{3}(g) \longrightarrow \mathrm{N}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g)} \\ {\text { c. } \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm\ {NO}(g)} \\ {\text { d. } 2 \mathrm\ {KClO}_{3}(s) \longrightarrow 2 \mathrm\ {KCl}(s)+3 \mathrm{O}_{2}(g)}\end{array}\end{equation}

PART $\mathrm{A} : \Delta H^{\circ}=64.5 \mathrm{kJ}, \Delta G^{\circ}=69.0 \mathrm{kJ}, \Delta S^{\circ}=-12.7 \mathrm{J} / \mathrm{K},$ and nonspontaneous
at all temperatures.
PART $\mathrm{B} : \Delta H^{\circ}=187.2 \mathrm{kJ}, \Delta G^{\circ}=192.2 \mathrm{kJ}, \Delta S^{\circ}=-16.4 \mathrm{J} / \mathrm{K},$ and
nonspontaneous at all temperatures.
PART $\mathrm{C} : \Delta H^{\circ}=182.6 \mathrm{kJ}, \Delta G^{\circ}=175.2 \mathrm{kJ}, \Delta S^{\circ}=24.8 \mathrm{J} / \mathrm{K},$ nonspontaneous,
and raise temperature.
PART $\mathrm{D} : \Delta H^{\circ}=-77.6 \mathrm{kJ}, \Delta G^{\circ}=-224.4 \mathrm{kJ}, \Delta S^{\circ}=494.6 \mathrm{J} / \mathrm{K},$ and
spontaneous.

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## Video Transcript

So this question is multiple parts of Mrs Devine Don't that each night Dr s Not and of Jean Operation Thes Reactions listed also wants us to say if direction is spontaneous or not. And if the temperature change would help make it spontaneous if it's known spontaneous so the band. So let's just start with a You have methane going to see to age six because age to gas, find out h not bye. Doing h of formation of products, madness, H information, reactions. And then you also see the account for the mole coefficient. So her reactions you want to buy back to really nothing said What it looks like is you find the tables in the back of your book and you look the numbers in. So you have 84.68 plus zero for hydrogen gas minus two. Counting front to here times negative. 74.6. And that gives us 64. 25 killed. Jules, you do the same thing heard at the S. It's 2 29 plus 1 30 0.7 minus two times 1 86.3 And that gives us named 12.7 jewels for Kelvin or negative 0.127 killed Jules Kelvin. And there is under that. It's because of the Asian eyes and killed Jules. So now I find the Gino. I'm doing that the age minus Tito the s. So we'll do. 64 45 minus 2 98 Kelvin, which is 25 degrees c times that the s not which is tango zero. Wait. 012127 And that gives us 68.3. Killer. Jules, this reaction is known spontaneous because the sinus positive and so we need to think of temperature would help make this direction spontaneous. But since both don't the h is positive and Delta s is positive or don't test is negative. So this overall values positive and tea is always positive. You can't make tea negative, even though you can decrease temperature so you can never make this value. No, I'm positive. So temperature has no effect in making this spontaneous, so no. Okay, so for B. Yeah, two at age three, going thio into age four plus age too. So I'm not gonna go through the whole process again for what you get. Is that h not equals 1 87 You'd do the same thing we did in part a, um the other s night cools negative. Zero point 164 And don't g equals 1 92 killed, Jules. And again, they'll take just positive. Delta s is negative centers. It's not both non spontaneous and no, you can't change temperature to extraction. Spontaneous. See, you have a connection. Gas those oxygen gas going to and make sure your accounting for the two on this one it's end of the age equals 1 82 killer. Jules, the s equals 0.435 killed Jules for Calvin and Delta G not equals 52.9 killed. Jules. So this stone on spontaneous. But since Delta H is positive and that s not as positive, we want to increase. Delta s not overcome. Dealt agent. Not so increased temperature to make spontaneous Get this panties were negative. Delta G value. So for D to k c l o R. Three going to K c l 1st 3 18 to make sure you account for all the co visions in this reaction, um, that the age not equals negative. 77.6 killed Jules, don't it? That's not equals. 0.4 94 killed Jules for Calvin and then go to Gina. So I wrote that equals named of 2 24 0.9 Killer. Jules. So this is negatives of this direction spontaneous.