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Published byMichael Nute Modified over 2 years ago

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Hess’ Law Extra Practice Problems

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1.From the following enthalpy changes, S (s) + 3 / 2 O 2 (g) SO 3 (g) H = 395.2 kJ 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) H = 198.2 kJ calculate the value of H for the reaction S (s) + O 2 (g) SO 2 (g) flip same S (s) + 3 / 2 O 2 (g) SO 3 (g) H = 395.2 kJ 2 SO 3 (g) 2 S (s) 2 3 2 SO 2 (g) + O 2 (g) H = +198.2 kJ 2 2( ) 2 +2 O 2 (g) 2 SO 2 (g) H = 592.2 kJ 2 = 296.1 kJ

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2.From the following enthalpy changes, H 2 (g) + ½ O 2 (g) H 2 O (ℓ) H = 285.8 kJ N 2 O 5 (g) + H 2 O (ℓ) 2 HNO 3 (aq) H = 76.6 kJ ½ N 2 (g) + 3 / 2 O 2 (g) + ½ H 2 (g) HNO 3 (aq) H = 174.1 kJ calculate the value of H for the reaction 2 N 2 (g) + 5 O 2 (g) 2 N 2 O 5 (g) flip same ½ N 2 (g)+ 3 / 2 O 2 (g)+ ½ H 2 (g) HNO 3 (aq) H = 174.1 kJ 2 HNO 3 (aq) N 2 O 5 (g) + H 2 O (ℓ) H = +285.8 kJ H = +76.6 kJ H 2 (g) + ½ O 2 (g)H 2 O (ℓ) flip 12.5 1 22( ) 3 N 2 (g) + 2.5 O 2 (g) N 2 O 5 (g) H = 14.2 kJ 2 5 2 2( ) = 28.4 kJ

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3.From the following enthalpy changes, C (s) + O 2 (g) CO 2 (g) H = 393.5 kJ H 2 (g) + ½ O 2 (g) H 2 O (l) H = 285.8 kJ C 5 H 12 (g) + 8 O 2 (g) 5 CO 2 (g) + 6 H 2 O (l) H = 3536 kJ calculate the value of H for the reaction 5 C (s) + 6 H 2 (g) C 5 H 12 (g). same flip C (s) + O 2 (g) CO 2 (g) H = 393.5 kJ same H 2 (g) + ½ O 2 (g) H 2 O (l) H = 285.8 kJ C 5 H 12 (g) + 8 O 2 (g) H = 5 CO 2 (g) + 6 H 2 O (l)+3536 kJ 5 5 5 5( ) 6 3 66( ) 5 C (s)+6 H 2 (g) C 5 H 12 (g) H = 146.3 kJ

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4.From the following enthalpy changes, CO (g) + SiO 2 (s) SiO (g) + CO 2 (g) H = +520.9 kJ 3 SiO 2 (s) + 2 N 2 O (g) + 8 CO (g) 8 CO 2 (g) + Si 3 N 4 (s) H = 461.1 kJ calculate the value of H for the reaction 5 CO 2 (g) + Si 3 N 4 (s) 3 SiO (g) + 2 N 2 O (g) + 5 CO (g) flip same CO (g) + SiO 2 (s) SiO (g) + CO 2 (g) H = +520.9 kJ 8 CO 2 (g) + Si 3 N 4 (s) 5 CO 2 (g) 33 3 SiO 2 (s) + 2 N 2 O (g) + 8 CO (g) H = +461.1 kJ 3 3( ) +Si 3 N 4 (s) 3 SiO (g) H = +2023.8 kJ 3 5 5 2 N 2 O (g) 5 CO (g) + +

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5. From the following enthalpy changes, H 2 (g) + ½ O 2 (g) H 2 O (l) H = 285.8 kJ SO 3 (g) + H 2 O (l) H 2 SO 4 (l) H = 132.5 kJ H 2 SO 4 (l) + Ca (s) CaSO 4 (s) + H 2 (g) H = 602.5 kJ Ca (s) + ½ O 2 (g) CaO (s) H = 634.9 kJ calculate the value of H for the reaction CaO (s) + SO 3 (g) CaSO 4 (s). same flip same SO 3 (g) + H 2 O (l) H 2 SO 4 (l) H = 132.5 kJ H 2 (g) + ½ O 2 (g) H 2 O (l) H = 285.8 kJ H 2 SO 4 (l) + Ca (s) CaSO 4 (s) + H 2 (g) H = 602.5 kJ CaO (s) H = Ca (s) + ½ O 2 (g) +634.9 kJ same SO 3 (g)+CaO (s) CaSO 4 (s) H = 385.9 kJ

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