Gibbs energy change, AG if the enthalpy change is positive and the entropy chang

Question

Gibbs energy change, AG if the enthalpy change is positive and the entropy change is negative, which of the follow ing statements best describes the reaction spontaneity? A) The reaction is always spontaneous. B) The reaction is spontaneous at high T but nonspontaneous at low T C) The reaction is spontaneous at low T but nonspontaneous at high T D) The reaction is never spontaneous E) None of these statements is applicable. 2. Using the data table provided (Page 5), which of these species would rank in order as third with respect to stability to decomposition back to the elements at 25°C and I atm: PbS(s),04g). MgCl4s).C.HJR).NOg). 3. The equilibrium constant for the equation HNo, (aq) + H,0 (l)-11,0. (aq) + No,. (aq) isK. = 5.6×104 M at 25.00. what is the value of 30,-a1250°C when IHO.|slo:1-15x10" M and HNO,1 0.75 M? A)-13.0 KJ mol' B)-16.9 Jmol C)-18.6J-mol D)-315 kJ-mol 4. When metal A is placed in a solution of metal ions B, a reaction occurs between A and B3. and metal ions A appear in the solution. When metal B is placed in acid solution, gas bubbles form on its surface. When metal A is placed in a solution of metal ions C, no reaction occurs. Which of the following reactions would not occur spontaneously? 2H-(aq) HAs) Arap C(s) + B (aq) H(g) + Ba(aq) D) A(s) + C) Bis) + C"(aq) E) Bis) + 2H'(aq) +

Explanation / Answer

1) we know that

DeltaG = DeltaH- TDeltaS

DeltaH = positive

DeltaS = negative

so DeltaG = Positive(always)

The reaction will never be spontaneous.

2) Remember

If DeltaH of formation is high and negative then the compound will be stable to decomposition

If DeltaH of formaiton is low and negative, it will be stable

If deltaH of formation is positive, it will be unstable

PbS = -100.4

O2 = 0

MgCl2 = -641

C2H4 = 52.26

NO= 90.25

So highest to lowest stability order will be

MgCl2 > PbS > O2 > C2H4 > NO

Answer is O2

3) DeltaG = -RTlnK

So DeltaG = -8.314 X 298 X ln (5.6X10^-4) = -12.848 KJ / mole = -13KJ / mole

4) This is based on redox concept

Observations are

1) When A is placed with B+2 gets converted to A+2 (which means that B is a good oxidizing agent)

2) B is placed in acid then gas bubbles out (which must be hydrogen)

B + 2H+ --> B+2 + H2

This means it is good reducing agent then Hydrogen

3) When Metal A is placed in C+2 no reaction means A will not gets oxidized by C+2 , so from 1) B is better oxidizing agent then C or C is a good reducing agent than B. So C may also reduced H+.

The reaction which will not occur spontaneously will be :

C) C+2 + B --> B+2 + C (oxidation of B, not possible)

Related Questions

Navigate

• Browse (All)
• Browse G
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.