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[匿名]

2011-11-24 3:31 am

Calculate a lattice energy for CaH2(s) in kilojoules per mole using the following information:

Eea for H(g)= -72.8kj/mol,
Eil for Ca(g)=+589.8kj/mol,
Ei2 for Ca(g)=+1145kj/mol,

Heat of sublimation for Ca(s) = +178.2kj/mol,
Bond dissociation energy for H2(g)=+435.9kj/mol,
Net energy change for the formation of CaH2(s) from its elements= -186.2kj/mol

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回答 (1)

fooks

2011-11-24 8:51 am

✔ 最佳答案

Ca^2+(g) + e^-(g) → Ca^+(g) .... ΔH = -(+1145 kJ/mol)
Ca^+(g) + e^-(g) → Ca(g) .... ΔH = -(+589.8 kJ/mol)
Ca(g) → Ca(s).... ΔH = -(+178.2 kJ/mol)
2H^-(g) → 2H(g).... ΔH = -2(-72.8 kJ/mol)
2H(g) → H2(g) .... ΔH = -(+435.9 kJ/mol)
Ca(s) + H2(g) → CaH2(s) .... ΔH = -186.2 kJ/mol

Sum up the above thermochemical equations, and cancel Ca^+(g), Ca(g), Ca(s),2H(g) and H2(g) on the both sides.
Ca^2+(g) + 2H^-(g) → CaH2(s) .... ΔHlatt

Lattice energy for CaH2(s), ΔHlatt
= -1145 - 589.8 - 178.2 + 2(72.8) - 435.9 - 186.2
= -2389.5 kJ/mol

參考: Tsui

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