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

Gibbs Free Energy (?G°)

Gibbs free energy combines enthalpy and entropy changes to predict the spontaneity of a reaction at constant temperature and pressure. Calculated using the relation ?G° = ?H° - T?S°, it determines whether a process can occur without external intervention. A negative ?G° indicates a thermodynamically favorable (spontaneous) reaction, whereas a positive value signals non-spontaneity under standard conditions.

Standard Enthalpy Change (?H°)

Standard enthalpy change represents the amount of heat absorbed or released during a reaction under standard conditions. It is a fundamental thermodynamic property calculated using the standard enthalpies of formation for reactants and products, offering insight into whether a reaction is exothermic or endothermic. This concept is crucial for understanding energy changes in chemical reactions and for predicting reaction behavior in various temperature regimes.

Standard Entropy Change (?S°)

Standard entropy change refers to the change in disorder or randomness associated with a reaction at standard conditions. It is determined by comparing the standard molar entropies of the products and reactants, and it is essential in evaluating the overall change in system disorder during a chemical transformation. This concept is critical for analyzing how the distribution of energy among particles shifts as a reaction progresses.

Reaction Kinetics and Activation Energy

Reaction kinetics focuses on the rate at which a chemical reaction proceeds and the factors that influence this rate, such as activation energy. Even if a reaction is thermodynamically favorable (negative ?G°), a high activation energy can create a kinetic barrier that prevents the reaction from occurring rapidly. This distinction explains why certain reactions, like the decomposition of NO in the atmosphere, do not proceed spontaneously despite being thermodynamically viable.

Thermodynamic versus Kinetic Control

Thermodynamic control deals with the overall energy change (stability) of a reaction, while kinetic control is concerned with the rate at which the reaction approaches equilibrium. A process may be thermodynamically spontaneous but still be kinetically inhibited by a high activation energy barrier, leading to slow reaction rates. This principle helps in understanding why some products, once formed, remain stable in environments where the reverse reaction is possible but kinetically hindered.

Transcript

00:01 Okay, so we have the following equation right here, n2 gas plus o2 gas yields 2 and o gas.

00:12 So they want us to determine the delta h, the delta s, and the delta g.

00:17 So in order to calculate all three of these, all you need to do is take the, so let's just do delta h first, actually.

00:24 So the delta h of the reaction is equal to the sum of the delta h on the product side.

00:34 Minus the sum of the delta h on the reactant side.

00:41 So let's start with the product side.

00:45 So delta h of the reaction, we have two moles of no, and the delta h of no is 90 kilo per mole.

00:55 Now minus, so we have one mole of n2 and the delta h is 0, plus one mole of oxygen and the delta h is 0.

01:05 So we don't even need to plug this in the calculator because 2 times 90 ,000.

01:08 Is 180 and 180 minus 0 is 0 so it's 180 kilojoules now for the next part we have delta s so delta s is the same thing is pretty much the sum of the delta s on the product side minus the sum of the delta s on the reacting side so let's start with the product side so we have two moles of n o the delta s of n o is 2 11 jou so minus 1 mole of n2 delta s is 192 plus one mole of 02, delta s is 205.

01:51 Right, we plug this in the calculator and we should get 25 joules.

01:57 Now for the delta g, delta g is also the same thing as the sum of delta g on the product side minus the sum of delta g on the reacting side...

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