In which of the following processes would one expect DeltaS to have the value cl
ID: 1000155 • Letter: I
Question
In which of the following processes would one expect DeltaS to have the value closest to zero? [A] CH_3C(O)H(g)+ 5/2 O_2(g) rightarrow 2CO_2(g) + 2H_2O(g) [B] C_2H_4(g) + Br_2(l) rightarrow C_2H_4Br_2(l) [C] 2NO(g) + O_2(g) rightarrow 2NO_2(g) [D] N_2(g) + O_2(g) rightarrow 2NO(g) [E] H_2(g) + I_2(s) rightarrow 2HI(g) 17. Which of the following is true in the sublimation of one mole of dry ice? 1. The entropy decreases. 2. The entropy increases. 3. The enthalpy increases. 4. The enthalpy decreases. [A] 1 only [B] 2 only [C] 1 and 3 only [D] 2 and 3 only [E] 1 and 4 only 18. Which of the following processes involve an increase in entropy? 1. Br_2(l) rightarrow Br_2(g) 2. (NH_4)_2Cr_2O_7(s) rightarrow N_2(g) + 4H_2O(l) + Cr_2O_3(s) 3. 2KClO_3(s) rightarrow 2KCl(s) + 3O_2(g) 4. 2HgO(s) rightarrow 2Hg(l) + O_2(g) [A] 1 only [B] 2 only [C] 3 and 4 only [D] 1, 3, and 4 only [E] 1, 2, 3, and 4 19. What is equal to DeltaH at equilibrium? [A] TDeltaS [B] DeltaH [C] DeltaG [D] DeltaU [E] DeltaS 20. The temperature of water decreases on the dissolution of NH_4NO_3. From this observation we can conclude that the solution process would be best described as [A] exothermic with a negative free energy change. [B] exothermic with a negative entropy change. [C] endothermic with a positive entropy change. [D] endothermic with a negative entropy change. [E] exothermic with a positive entropy change.Explanation / Answer
Solutions:-
(16) theoretically, if the number of gaseous molecules are equal on both sides then delta S is zero.
for reaction D, we have two molecules of gases on both sides so the delta S would be zero. No other equation has equal molecules of gases on both sides. So, the correct choice is (D).
(17) Dry ice is frogen that is solid CO2. in sublimation this solid changes into gas. So, it is an endothermic reaction and entropy increases since its going from solid to gas.
CO2(s) + Heat <----------> CO2(g)
Entropy increases as the gas is more disordered than solid.
There is equilibrium between solid and gas, so, delta H = T x delta S
since delta S is increasing, delta H(enthalpy) will also incraese.
Hence the correct choice is (D) 2 and 3 only.
(18) This is similar to number 16. So, the entropy change would be positive if we have more gases on product side than reactant side.
in all the given reactions we have gases only on the product side, so the entropy is incraesing for all of them.
Correct choice is (E) 1,2,3 and 4.
(19) From Gibb's free energy equation, delta G = delta H - T* delta S
at equilibrium, delta G = 0
So, 0 = H - T*delta S
delta H = T*delta S
so, the correct choice is (A) T*delta S.
(20) Dissolition of NH4NO3 dicreases the water temperature it means the process is endothermic. Dissolution of NH4NO3 takes place means it breaks into its ions. Here the system is going to be more disordered from more ordered so the entropy change would be positive.
So, the correct choice is, (C) endothermic with a positive entropy change.