Which of these reactions has Delta S degree > 0? PCl_5(g) rightarrow PCI_3 (g) +

Question

Which of these reactions has Delta S degree > 0? PCl_5(g) rightarrow PCI_3 (g) + CI_2 (g) H_2(g) + O_2(g)rightarrow H_2O_2 (aq) H2O(l) rightarrow H2O(s) S_8(1) rightarrow S8(s) 3H_2(g) + N_2(g) rightarrow 2NH_3 (g) The entropy will usually increase when a reaction results in a decrease in the number of moles of gas. a molecule is broken into two or more smaller molecules. a liquid change to a solid. a gas changes to a solid. None of the above All of the following have a H_r degree value of zero at 25 degree C and 1.0 atm except: Hg(l) All of the following have a G_r degree value of zero at 25 degree C and 1.0 atm except: H_2(g) If Delta H for a reaction is positive, the reaction rate is generally very fast. H degree (products) is smaller than H degree (reactants). the reaction rate is generally very slow. the process is exothermic H degree (reactants) is bigger than H degree (products). If AG degree for a reaction is negative ... the reaction rate is generally very slow. the reaction is not spontaneous G degree (products) is bigger than G degree (reactants). the process is exothermic the reaction is spontaneous N_2(g) Ne(g) FeO(s) Fe(s) hg(l) All of the following have a G_r degree value of zero at 25 degree and 1.0 atm except: H_2(g) Na(s) Fe(s) H_2O(l)

Explanation / Answer

1. deltaS > 0 if the sum of moles of products are greater than moles of reactants. Because while calculating entropy change, we calculate the entropy of products by multiplying the entropy of a given produtct with its coefficients. As a result, higher the coefficient, higher the number of moles, higher the entropy change

Hence in PCl5(g)----> PCl3(g)+ Cl2(g), there is an increase in number of moles due to the reaction. Product moles are greater than reactant moles. Hence entropy change is >0 ( A is correct answer)

2. Entropy change increase when ever the molecules breaks down into two molecules as shown in the above example. ( B is correct). Entropy is degree of disorder and hence entropy decreases during a gas becoming a liquid and liquid becoming solid.

3. All elements in their standard states will have zero Hf. FeO (s) is not an element and hence will have non zerop Hf. ( C is correct)

4. for the same reason mentioned above, Gf for water is not zero.(D is correct)

5.deltaH = enthalpy of products- enthalpy of reactants. Hence +ve enthalpy suggests endothermic reaction. enthalpy of products has to be greater than reactants.

6. deltaG is -ve suggest instantaneous reaction. E is correct.

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