Using data from Appendix 4 calculate ΔH^∘, ΔS^∘, and ΔG^∘ for the reaction N2(g)+O2(g) ⟶2 NO(g).

Using data from Appendix 4 calculate ΔH^∘, ΔS^∘, and ΔG^∘...

Key Concepts

Thermodynamic vs Kinetic Control

This concept differentiates between the conditions that determine the final equilibrium state of a reaction (thermodynamics) and those that affect the rate at which the reaction proceeds (kinetics). Thermodynamics, as described by ?G°, tells us whether a reaction is energetically favorable, while kinetics focuses on the activation energy barrier that must be overcome for the reaction to occur. In scenarios where reactants form products under high-temperature conditions—as in an automobile engine—a reaction can proceed rapidly; however, at lower temperatures, even thermodynamically favorable reactions may be hindered by high activation barriers, making the reverse process slow or negligible.

Standard Enthalpy Change (?H°)

This concept refers to the heat absorbed or released during a chemical reaction under standard conditions (usually 1 bar, 298 K). It is calculated using the standard enthalpies of formation of the reactants and products. A positive ?H° indicates an endothermic reaction (heat absorbed), while a negative ?H° indicates an exothermic reaction (heat released). Understanding ?H° is essential for predicting whether energy is required or released during the transformation of substances in a reaction.

Standard Entropy Change (?S°)

Standard entropy change quantifies the change in disorder or randomness as a reaction progresses under standard conditions. It is determined by the difference between the total standard entropy of the products and that of the reactants. A positive ?S° generally indicates an increase in randomness (for example, an increase in the number of gas molecules), while a negative ?S° suggests a decrease in disorder. This concept helps in understanding how the distribution of energy and particles changes during a chemical reaction.

Standard Gibbs Free Energy Change (?G°)

The standard Gibbs free energy change combines the effects of enthalpy and entropy to determine the overall spontaneity of a reaction under standard conditions. Expressed as ?G° = ?H° - T?S°, it indicates whether a reaction is thermodynamically favorable. A negative ?G° signifies a spontaneous process, while a positive ?G° means the reaction is non-spontaneous under standard conditions. This parameter is crucial for predicting the feasibility of chemical reactions and understanding their equilibrium positions.

Transcript

00:01 Okay, so problem number 48 is asking us to find the change in empathy, entropy, and gibbs free energy for this reaction.

00:12 So anytime we're trying to find delta h, dotag, or delta s for an entire reaction, we want to take the individual, delta h, delta g, and delta s's of formation for each of the elements.

00:29 And then in total limineally, so what we want to do is we want to take our products.

00:35 This one we want to subtract our reactants.

00:39 So it's always products minus reactants.

00:42 So this will be products minus reactants.

00:51 And it doesn't matter what we start with.

00:55 Let's just start with finding the delta age of reaction.

01:02 So it says to use appendix 4.

01:04 So if you look in appendix 4, you'll find the delta -h of formation for each of the individual atoms.

01:10 So what we want to do is we want to take the delta -h of the products.

01:15 So in this case, it's just an no gas, but we have two of them.

01:20 So we're going to have two times, and then we're going to use the delta -h for that.

01:25 And if we look that up, it's just 90 kilojoules per mole.

01:35 And then minus the reactants.

01:40 So let's start with n2.

01:41 We have one, one of those, so just 1 times n2.

01:46 And if you look up the delta h of formation of n2, it's just 0.

01:53 So actually, 0 kittal joules per mole.

01:58 And then the delta h of formation for 02 is also 0.

02:02 So that's really nice.

02:04 In this case, this whole thing cancels out.

02:11 And it's just zero.

02:12 So that means that the delta h of the reaction.

02:17 And this is at standard conditions but the delta h of the entire reaction is just two times that 90 kilojoules per mole which is of course just 180 kilojoules per mole so this will be our delta h now um next we want to find either delta g or delta s of the reaction and that's going to be the same thing.

02:58 We're going to look at the products and we're going to subtract the reactants and we're going to take the individual delta gs of each thing.

03:05 So what we're going to do is we're going to do delta g a reaction next because if we look at the table, we'll find that that delta g is for n2 and o2 or also zero...

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