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4.4 Review Questions 1. Indicate whether each of the following changes is endothermic or exothermic: (a) Barbecuing a steak
(b) Freezing a tray full of water to make ice
(c) Neutralizing an acid spill with baking soda
(d) Making a grilled cheese sandwich
(e) Lighting a barbecue igniter
(f) Condensing water on a mirror
2. Convert the following ∆H notation equations into thermochemical equations using the smallest whole number coefficients possible: (a) ½ C3H8(g) ➝ ½ C3H8(l) ∆H = –175 kJ/mol
(b) Li(s) + ½ CaCl2(aq) ➝ LiCl(aq) + ½ Ca(s) ∆H = –362 kJ/mol
(c) 2 B(s) + 3 H2O(g) ➝ B2H6(g) + 3/2 O2(g)
(d) ½ P4(s) + 3 Cl2(g) ➝ 2 PCl3(s) ∆H = –613 kJ/mol
(e) NH3(g) + 3/2 N2O(g) ➝ 2 N2(g) + 3/2 H2O(l)
(f) ½ Fe3O4(s) + ½ CO(g) ➝ 3/2 FeO(s) + ½ CO2(g) ∆H = 9 kJ/mol
∆H = 762 kJ/mol
∆H = –505 kJ/mol
3. Convert the following thermochemical equations into ∆H notation using the smallest whole number coefficients possible. (a) C(s) + 2 H2(g) + ½ O2(g) ➝ CH3OH(l) + 201 kJ/mol
(b) ½ Cu(s) + ½ H2(g) + ½ O2(g) ➝ ½ Cu(OH)2(s) + 225 kJ/mol
(c) 389 kJ/mol + ½ Sb4O6(s) + 3 C(s) ➝ 2 Sb(s) + 3 CO(g)
(d) 56 kJ/mol + NO2(g) ➝ NO(g) + ½ O2(g)
(e) PCl3(g) + ½ O2 (g) ➝ Cl3PO(g) + 286 kJ/mol
(f) F2(s) + ½ O2(g) ➝ OF2(g) + 22 kJ/mol
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Chapter 4 Expressing and Measuring Chemical Change 195