I missed a day of class and our test is coming up after the weekend. This seems

Question

I missed a day of class and our test is coming up after the weekend. This seems pretty simple, I just can't figure it out by looking at it. Please show steps and explain the answers. Thank you!

Classify the following reactions as either…
- always spontaneous
- never spontaneous
- spontaneity temperature dependent

1. H2O2(g) –> H2O(g) + 1/2O2(g); Hºrxn = -106kJ, Sºrxn = +58kJ

2. N2(g) + 3Cl2(g) –> 2NCl3(g); Hºrxn = +460kJ, Sºrxn = -275 JK-1

3. N2F4(g) –> 2NF2(g); Hºrxn = 85 kJ, Sºrxn = 198 JK-1

4. N2(g) + 3F2(g) –> 2NF3(g)l Hºrxn = -249 kJ, Sºrxn = -287 JK-1

a. Determine the equilibrium temperature for each reaction in part that has a temperature-dependent spontaneity.

b. For each reaction that has a temperature-dependent spontaneity, indicate whether the reaction is spontaneous above or below its equilibrium temperature

Explanation / Answer

Let us begin with entropy (delta So), the disorder of a system. It takes energy to force order on any system. If you have to pump energy in, then the reaction isn't very spontaneous. So, you want a positive entropy, which means that disorder is increasing.

Secondly, enthalpy delta Ho (heat.) If a reaction evolves heat, then it is a favorable reaction. However, if you have to put heat into it for the reaction to go, then it wasn't very spontaneous. Remember that if you have to add heat, the delta H is positive; if heat evolves on its own, the delta H is negative.

So, a reaction with positive S and a negative H is spontaneous.

delta G = delta H - T delta S [delat G always -ve for spontaneous reaction]

So,

1. Is a spontaneous reaction

2. Non-spontaneous reaction.

3. Endothermic reaction. Spontaneous at very low temperature <0.

4. Non-spontaneous reaction.

a. The equilibrium temperature would be when

delta G = 0

So,

1. T = 1.83 K

2. Non-spontaneous

3. T = -0.43 K

4. Non-spontaneous reaction

b. 1. Spontaneous above equilibrium temperature.

2. Non-spontaneous reaction

3. Spontaneous below equilibrium temperature

4. Non-spontaneous reaction

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