The Ostwald process for the commercial production of nitric...

The Ostwald process for the commercial production of nitric acid from ammonia and oxygen involves the following steps: $$\begin{array}{c}4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \\3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(i) \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g)\end{array}$$ a. Use the values of $\Delta H_{\mathrm{f}}^{\circ}$ in Appendix 4 to calculate the value of $\Delta H^{\circ}$ for each of the preceding reactions. b. Write the overall equation for the production of nitric acid by the Ostwald process by combining the preceding equations. (Water is also a product.) Is the overall reaction exothermic or endothermic?

The Ostwald process for the commercial production of nitric acid from ammonia and oxygen involves the following steps:
$$\begin{array}{c}4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \\3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(i) \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g)\end{array}$$
a. Use the values of $\Delta H_{\mathrm{f}}^{\circ}$ in Appendix 4 to calculate the value of $\Delta H^{\circ}$ for each of the preceding reactions.
b. Write the overall equation for the production of nitric acid by the Ostwald process by combining the preceding equations. (Water is also a product.) Is the overall reaction exothermic or endothermic?

Key Concepts

Exothermic and Endothermic Reactions

These terms describe the heat exchange in chemical reactions. Exothermic reactions release heat into the surroundings, resulting in a negative enthalpy change, while endothermic reactions absorb heat, resulting in a positive enthalpy change. Determining whether a reaction is exothermic or endothermic is crucial for understanding its energetics and practical implications in industrial processes.

Reaction Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. It is critical for combining individual reactions correctly, ensuring that the number of atoms for each element is conserved and that the overall reaction accurately reflects the process being described.

Industrial Chemical Process

The Ostwald process is an industrial method for producing nitric acid from ammonia and oxygen. It illustrates the application of chemical principles on a large scale, involving sequential reactions, catalysis, and energy management. Understanding such processes is important in both academic and industrial chemistry, emphasizing the translation of laboratory-scale reactions to commercial production.

Standard Enthalpy of Formation

This concept involves the heat change when one mole of a compound is formed from its elements in their standard states. It provides the necessary data points for calculating reaction enthalpies and is essential for determining whether a chemical reaction absorbs or releases heat.

Hess's Law

Hess's Law states that the total enthalpy change of a chemical reaction is independent of the pathway taken, as long as the initial and final conditions are the same. This principle allows for the calculation of overall reaction enthalpies by summing the enthalpy changes of individual steps in multi-step reactions, such as those in the Ostwald process.

Transcript

00:01 So this is one of those questions that is something kind of frustrating to work through, because it's really tedious, but basically what we need to do is we need to write out each equation and then look up the delta h of formation values for each of the reactants.

00:14 And so, for example, i've already done this for all the reactants.

00:18 This is what you'll look up fine if you look up at the table.

00:20 A couple of things to note.

00:22 Oxygen in its normal state.

00:24 It's a gasey state.

00:25 I didn't write the states here because that would have a really long time to do.

00:29 They're almost all gas, but that does matter.

00:33 The delta -age formation is different based on what say it is.

00:36 Anyways, oxygen and its gaseous state here is zero, just like any element.

00:41 It's a common state at 25 degrees celsius, one atmosphere will be zero.

00:47 And so anyways, what we do is to figure out the delta h of this step is we take the products minus the reactants.

00:53 That's a term, like a phrase always remember if you're not short to.

00:57 Products minus reactants so we first take four times 90 .2 four because we have this coefficient here times 90 .2 because you know that's our delta age formation then we have plus six times negative 241 so we have our products here now minus reactants well minus we have four times the negative 46 and then zero and so if you do that delta h will equal negative 908 kilojoules.

01:34 All these were in kilojoules.

01:36 Should have made that clear.

01:38 And so we do the same thing for all of these.

01:40 So delta h for this one is going to be 2 times 33.

01:44 So products minus now react is 2 times 90 .2.

01:49 And this should give us negative 112.

01:56 Something.

01:57 I don't know, just 12 kilojoules.

01:59 Have significant figures.

02:03 And then finally, our last one here, delta h is going to equal 2 times negative 207, from here and here, plus 1 times 90 .2.

02:17 So just 90 .2.

02:19 These are products now minus 3 times 33, and then minus 1 times negative 285.

02:30 You have to be careful, since you're subtracting the reactants, but sometimes they're negative.

02:36 And this, as in this case, you're really adding that value.

02:38 And so there's, you know, you have to be careful with your math.

02:42 You know, remember what you're doing.

02:44 But either way, this is going to come out to a negative 140 kilojoules.

02:47 And so now our next step is to look at all three of these reactions, which i've rewritten, and see how do they come together in terms of making one total reaction.

03:00 Now, well, what's being happened here is, we're producing nitric acid.

03:11 So these equations aren't exactly balanced.

03:17 And so what we want here is we want some of these intermediates to cancel out.

03:22 Specifically, we're told that we have water as a product, so water here.

03:30 And it's going to some of these waters over here are going to cancel it out.

03:34 And we're told that these are our reactants, ammonia and oxygen.

03:37 And so the things that we want to look to cancel out are these interneous.

03:41 We have this nitric oxide that we want to cancel out with this one.

03:47 We have this n -o -2 that we want to cancel out with this n -o -2...

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