Consider what happens when a piece Of zinc is added to a solution of nitric acid

Question

Consider what happens when a piece Of zinc is added to a solution of nitric acid reacts with the zinc you see a plume of red smoke. The smoke is produced when the nitrogen monoxide from the first reaction spontaneously reacts with oxygen gas in the air to form the red gas nitrogen dioxide. The reactions for this process are shown below: Reaction 1: 3Zn(s) + 8HNO_3(aq) rightarrow 3Zn(NO_3)_2M(aq) + 2NO(g) + 4H_2O(g) Reaction 2: 2NO(g) + O_2(g) rightarrow 2NO_2(g) (Given that Reaction 1 above is an exothermic reaction, what are the signs of the following thermodynamic parameters for Reaction 1? delta Ssys > 0. delta Ssurr less than 0, delta Sunrv > 0 delta Ssys > 0, delta Ssurr > 0, delta Suniv > 0 delta Ssys less than 0. delta Ssurr less than 0. delta Suniv less than 0 delta Ssys less than 0, delta Ssurr > 0, delta Suniv> 0 delta Ssys > 0, delta Ssurr less than 0, delta Suniv less than 0 Without doing any calculations, predict the signs of AH degree, AS* and AG degree for Reaction 2 above. delta H degree > 0. delta S* greater tahn 0. and delta G degree less than 0 delta H degree > 0. deltaS* less than 0, and delta G degree less than 0 delta H degree less than 0, delta S* less than 0, and delta G degree less than 0 delta H degree less than 0, delta S* less than 0. and delta G degree > 0 delta H degree less than 0. delta S > 0. and delta G degree > 0 Consider the decomposition of hydrogen fluoride: 2HF(g) rightarrow H_2(g) + F_2(g) Given that at 298K, delta G degree = 38.3 kj, (HF) = 0.070 atm, [H_2] = 0.025 atm and [F_2) = 0.0035 atm. which of the following statements about this reaction is correct at 298K? A Under these conditions the reaction will be spontaneous in the forwards direction. Under these condition will be spontaneous in the reverse direction. Under these condition, the system is at equilibrium.

Explanation / Answer

Q22 - Ans is D

explanation: For Exothermic reaction, (H is negative, heat produce) decrease the rondomness in system that means entropy of the system decrease [dS(system) will be -ve]and entropy of the universe increase [dS(univ) will be +ve].

dS(univ) = dS(system) + dS(sarrounding)

From this we can find the entropy of the Surroundings will increase [dS(sarrounding) will be +ve].

Q23. Ans is A

spontataneous reactions means that occurs without a external source of energy. This leads to relesae the energy (exothermic reactions) and according to 3rd law of thermodynamics, dS will increase in the spontanious reactions. If the reaction is exothermic, the products will have the less energy that means during the process the free energy of the molecule minimised. This leads to decrease in the free energy.  

Finally, dG -ve; dH +ve; dS +ve

Q24:

Ans is B

dG =dGo + R T ln Q

if a) dG = dGo i.e. system at equilibrium

b) dG > dGo i.e. system non spontaneous

b) dG < dGo i.e. system spontaneous

dG =dGo + R T ln Q

Q = [H2]*[F2] / [HF]^2 ---> lnQ= -4

dGo = 28 KJ

So dG > dGo i.e. system non spontaneous in forward direction but spontaneous in backword direction

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

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