Problem

Write an equation for the formation of each compo…

02:13

Problem 81 Hard Difficulty

Write an equation for the formation of each compound from its elements in their standard states, and find Hf for each from Appendix IIB.
a. NH3(g)
b. CO2(g)
c. Fe2O3(s)
d. CH4(g)

Answer

d.
$$
\Delta H_{r \times n}=-74.6 \mathrm{kJ} / \mathrm{mol}
$$

Allea C.

University of Maryland - University College

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Video Transcript

alright for this problem, we need to find the Standard Heat of formation for four different compounds. And we also need to write out an equation for the formation of each of these from their elements in standard States. So the first one is NH three. In order to make NH three, I am going to combine nitrogen gas. Remember that's diatonic plus hydrogen gas, Which is H two And that will give us an H3. Also in get the gas form. Just a quick balance of this. I have three hydrogen and two hydrogen. So we're going to get them to look alike by making them six. And that actually fixes the nitrogen as well. Now, when you hear Standard States and thermo chemistry, your delta H in your delta G should be zero for these guys. So the nitrogen and the hydrogen are going to be zero. I'm going to have a value for NH three. Remember when I find this, I'm really doing the some of the number of moles times my delta H of formation for my products minus the sum of the number of moles times the delta H of formation of my reactant. Now my reactant should be zero on all of these because they're in standard states. So all I really I'm doing is multiplying the number that I find for my product. But whatever coefficient is in front of it for NH three, we have to do two times -45.9, which is what I find at my table For the Delta H of NH three. This is going to give me a negative 91.8 killer jewels. In the 2nd 1. I'm making co two. So we're gonna go with carbon solid in its graphite form because that's the one that zero Plus 02. Which is gas Gives Me Co two. Also a gas. This is already balanced. So when I look up the number for CO two, that's going to be my answer, I get negative 3 93.51 Killer jewels. You have to do anything else to that one. For the third problem, we are making F. E. 203 to do that. I need solid iron plus oxygen gas. Make sure that you balance this Right now. Everything's messed up. So we're gonna look at the oxygen's of three and 2 which means I'm gonna have to get them to six. So I'll put it to there and a three here, that gives me four irons. Someone to put a four there again. Iron and oxygen or in standard states. So there's zero. I'm going to do two times negative 8 24 0.2 Which gives me a negative 1648 .4 Killer Jewels. The last one I am making CH four. So I need my carbon again. This is solid graphite plus hydrogen gas. That's going to give me CH four which is also a gas. The only thing I need to do to balance this is to put it to in front of H. two. When I look up the value for Ch four, that's gonna be my answer. That value is negative 74.6 killer jewels. Yeah.

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