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Exam 4 fall 2004 ANSWERS UPdated

# Exam 4 fall 2004 ANSWERS UPdated - Chemistry 105 Exam IV...

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Chemistry 105 Exam IV Fall 2004 Name: ______________________________ 1) Write a balanced chemical equation for the following reaction in basic solution: (5 points) CrO 4 -2 (aq) + SO 3 -2 (aq) Cr(OH) 3 (s) + SO 4 -2 (aq) (3e - + 5H + + CrO 4 -2 Cr(OH) 3 + H 2 O) x 2 (H 2 O + SO 3 -2 SO 4 -2 + 2H + + 2e - ) x 3 6e - + 10H + + 2CrO 4 -2 + 3H 2 O + 3SO 3 -2 2Cr(OH) 3 + 2H 2 O + 3SO 4 -2 + 6H + + 6e - 4H + + 2CrO 4 -2 + H 2 O + 3SO 3 -2 2Cr(OH) 3 + 3SO 4 -2 IN BASE 5H 2 O + 2CrO 4 -2 + 3SO 3 -2 2Cr(OH) 3 + 3SO 4 -2 + 4OH - 2) Write a balanced chemical reaction whose ΔH° is the ΔH f ° for liquid water. (5 pts) H 2 (g) + 1/2O 2 (g) H 2 O(l) 1

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3) For the combustion of glucose (C 6 H 12 O 6 ) the ΔH° = -2803 kJ/mol glucose. Given ΔH f ° for glucose is -1274 kJ/mol and that for CO 2 (g) is -393.505kJ/mol, determine the ΔH f ° of liquid water. (15 pts) C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(l) ΔH° = -2803 = 6(-393.505) + 6x – (-1274) = 6x – 1087.03 x = -286 kJ/mol 4) Assuming that the dissolving of sodium chloride in water is NEITHER exothermic nor endothermic and that the equilibrium constant for dissolving salt in water is 2.1x10 23 at
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