General Chemist try ll Part 2: Entropy is a focus of Topic 10. Entropy is given

Question

General Chemist try ll Part 2: Entropy is a focus of Topic 10. Entropy is given the symbol "S.The more mixed up things are, the higher the entropy. The more ways for a thing to be considered the same (how many ways can 3 pennies have 1 head and two tails), the higher the entropy. Entropy and disorder are closely related. As disorder increases, entropy increases. For example, consider your sock drawer. If all the socks are paired, the entropy is relatively low, but if the socks are all mixed up, the entropy is much higher. If there are many ways to amange the particles in the system, then there is greater disorder. Systems with greater disorder have greater entropy. Let's try and solve some problems: 1. Consider the following reactions. Use your intuition to complete the table below Does entropy what is the Reaction Does disorder sign of AS? increase or decrease? decrease? K (aq) Br (aq) KBr(s) 2. Lastly, use the table of thermodynamic functions to compute the AH and AS for the reactions in 1. Then using AH and AS and your knowledge of the second law, compute which reactions are spontaneous under standard conditions. Reaction AH AS AS universe Spontaneous 2H2(g) 02(g)- 2H20() CO2(s) co20g) K (aq) Br(aq) KBr(s)

Explanation / Answer

1) 2H2 (g) + O2(g) -----> 2H2O(l)

two gases becoming liquid , so disorder decreses, hence entropy decreses and Delta S is negative

2) CO2(s) ---> CO2(g)

solid becoming gas , disorder increases, entropy increases, delta S is positive.

3) K+(aq) + Br-(aq) ----> KBr(s)

two ions in solution become solid. Disorder decreases and entropy decreases. Thus delta S is negative

Q2) We know for a reaction delta H rxn = sum of deltaH of products - sum of delta H of reactants

similary

delta S rxn = sum of deltaS of products - sum of delta S of reactants

rxn delta H delta S

1) = 2(-285.8) = -571.6 kJ = 2(70) - [ 2(130.7) + 205.2]= - 83.8 J

2) = -393.52 -(-427.4)= 33.88kJ = 213.79 - 51.07 =162.72 J

3) = -393.8 -[-252.1-121] =-20.7 KJ = 95.9 -[101.2+82] =-87.3 J

rxn delta H delta S delta s universe spontaneity

1 - + + spontaneous

2) + + + spontaneous

3) - - - non- spontaneous

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