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Chemistry 1302A/B Lecture Notes - Lecture 6: Spontaneous Process, Randomness, Reversible Reaction

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School
Western University
Department
Chemistry
Course
Chemistry 1302A/B
Professor
Felix Lee

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Document Summary

Free energy your system and your surroundings together must increase the entropy of the universe. However, we are usually interested in the system itself, not the universe. Free energy examines the spontaneity of the system specifically and does so in a way that automatically takes in the energy change of the surroundings. Hsystem ideally, this is negative and the reaction gives off heat (if you have a reaction that breaks a lot of bonds you have to put in energy therefore in order to achieve and exothermic, bonds are breaking) Ssys ideally, this is positive and the order is random thus, lets try to relate these two conditions in a way that will be able to predict spontaneity. Combining the equations for a spontaneous process ( s equations and h equations) we get. Hsystem - t ssystem <0 for a spontaneous process. H - t s <0 this must hold true.

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Related Questions

Can anyone please explain why ∆S(surroundings) is < 0 ???

What do they mean ∆H (system) > 0? How/why did the system provide heat to dissolve the barium sulfate???

What equation are they drawing from? The only equation I can think of to relate this situation is ∆S(universe) = ∆S(system) + ∆S(surroundings) > 0 (if the process is spontaneous).Does it mean it's not spontaneous if the system provided heat? Maybe this has to do with lattices and hydration - I don't know.

apparently, ∆G for the dissolution of barium sulfate in water is positive.. is dissolution of a sparingly soluble salt always a non-spontaneous process? Thank you!

Please help me - thanks!

Model 1 – Spontaneous Processes Process Description Change in Enthalpy (∆H) Change in Entropy (∆S) Spontaneous? A Two pure → Homogeneous substances mixture ~ 0 Increasing Yes B Solute on Solute on one side of → both sides of membrane membrane ~ 0 Increasing Yes C Polypeptide → Individual chain amino acids Exothermic (negative) Increasing (positive) Yes D C3 H8 + 5O2 → 3CO2 + 4H2 O Exothermic Increasing Yes E 6CO2 + 6H2 O → C6 H12O6 + 6O2 Endothermic Decreasing No F Glucose → Starch Endothermic Decreasing No G Water → Ice Exothermic Decreasing Below 0 °C, yes Above 0 °C, no H Cold water (25 °C) → Hot water (60 °C) Endothermic Increasing Below 60 °C, no Above 60 °C, yes

Some of the processes in Model 1 are spontaneous—that is, they will occur without any additional work being done on the system. For example, a solute will diffuse across a membrane until the concentrations of both sides are equal. However, glucose will not spontaneously form from carbon dioxide and water in the atmosphere. The Second Law of Thermodynamics states that a process will be spontaneous when it results in an increase of total entropy in the universe. In other words, either the system or the surroundings must have an increase in entropy, or both. (Please note that the term “spontaneous” does not imply that the change will happen quickly. Rusting is spontaneous under the right conditions, but it can still occur very slowly.)

13. Predict the change in entropy of the surroundings for an endothermic reaction.

please help and explain... I am beyond lost on this assignment

1. A certain process has ∆H◦>0 and ∆S◦<0. Which of the following is a correct conclusion about this process

Non spontaneous at all T.

Spontaneous at high T / Spontaneous at low T / Spontaneous at all T / None of the above­­­­­­­­­­­­­­­­­­­

2. the formation constant for the reaction Ag+(aq)+2NH3(aq) ß-à Ag(NH3)2+(aq) is K=1.7x10^7 at 25 deg C. what is ∆G◦ (kJ/mol) at this temp

-23 / -18 / -3.5 / -1.5 / -41

3. Nitric oxide reacts with chlorine to form NOCL. What is the free energy (kJ) of the reaction at 277 dec C.

2NO(g) + Cl2(g) Ã 2NOCl(g)

+144 / -41.0 / -10.3 / -22.2 / +41.0

4. How much free energy is released or absorbed(kJ) when 95.0 g of ozone is produced.

3 O2(g)à 2 O3(g) ∆G◦ = +326 kJ

+645 / -323 / +95 / +323 / -645

5. Estimate the boiling point (deg C) of phosphoric acid? H3PO4(s)ßà H3PO4(l)

42 / 181 / 315 / -92 / 305

6. Calculate the ∆S◦ (J/K) for the reaction, SiCl4(g)+2Mg(s)à 2MgCl2(s)+Si(s)

+198 / -198 / +255 / -255 / +472

7. Calculate the equilibrium constant, K, for the following reaction at 25 deg C: CH4(g)+2H2O(g)ßà CO2(g) ∆G◦ =-113.6kJ

Which of the following results in a decrease in the entropy of the system

O2(g),300KÃ O2(g), 400K / H2O(s)Ã H3O(l) / N2(g)Ã N2(aq) / NH3(l)Ã NH3(g) / 2H2O2(g)Ã 2H2O(g)+O2(g)

8. Identify the incorrect statemtent?

When ∆G◦ >0, energy can be added to force a non-spontaneous to proceed.

When K>1, ∆G◦ <0.

Enthalpy is a good predictor of free energy.

Entropy of the universe increases in a spontaneous reaction

All of the above