Ex 2 Sp05 hints - Hints on Solving Q's for CHM 2046 Exam 2,...

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Hints on Solving Q’s for CHM 2046 Exam 2, Mar. 9, 2005. (This is keyed to Form Code A.) 1. Do you know what “ ) G f o ” means? Do you know the formula for iron(II) sulfate? Do you know that elemental sulfur is S 8 ? 2. “Least stable” means greatest tendency to change - as in dissolving readily or con- verting to a different substance. Thus, of the given choices, since CaCO 3 is much more stable than CaSO 4 •2H 2 O so long as the system is not acidic, 1 M NH 4 HCO 3 , which is mildly basic, offers the opportunity for CaSO 4 •2H 2 O to readily convert to CaCO 3 . If necessary, consider K for this conversion ( K = K sp CaSO 4 •2H 2 O/ K sp CaCO 3 = ~ 2000) to convince yourself. 3. For: H 2 O(s) H 2 O(l) at 25 o C, @ 1 atm (or 1 bar), it should be obvious that ) H r and ) S r are each “+” because, for this process “as written”, bonds are weakened (thus ) H r is endo) and “randomness” increases on conversion of (s) to (l) for any given material. And each of the following thermodynamic conditions also apply: (i) VP H 2 O(s) = VP H 2 O(l); (ii) ) G f o H 2 O(s) = ) G f o H 2 O(l); (iii) ) G r o = ) G r = 0; (iv) ) H f o H 2 O(s) is more exo than ) H f o H 2 O(l); (v) S o H 2 O(s) is “less +” than S o H 2 O(l). 4.
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Ex 2 Sp05 hints - Hints on Solving Q's for CHM 2046 Exam 2,...

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