Calculate the energy change for the formation of CaF₂(s) from its elements in their standard states and the following information: Ca(s) + F₂(g) → CaF₂(s) ?
Ca(s) → Ca(g) +179.3 kJ/mol
Ca(g) → Ca⁺(g) + e^- +589.9 kJ/mol
Ca⁺(g) → Ca²⁺(g) + e^- +1145 kJ/mol
1/2 F₂(g) → F(g) +79.0 kJ/mol
F(g) + e^- → F^-(g) -328.0 kJ/mol
CaF₂(s) → Ca²⁺(g) + 2 F^-(g) +2630 kJ/mol

Question

Quizplus · Accepted Answer

- First, we need to calculate the energy change for forming CaS1U1P12 from Ca(s) and S1U1B0(g): 
Ca(s) → Ca(g) +179.3 kJ/mol (reverse) 
Ca(g) → CaS1U1P1+S1S1P0(g)+ eS1U1P1-S1S1P0 +589.9 kJ/mol 
S1U1B0(g) + eS1U1P1-S1S1P0 → S1U1P1-S1S1P0(g) +328.0 kJ/mol (reverse) 
Adding the above equations, we get: 
Ca(s) + S1U1B0(g) → CaS1U1P12 +328.0 kJ/mol 
- Next, we need to calculate the energy change for forming FS1U1B12S1U1B0 from CaS1U1P12 and F(g): 
1/2 FS1U1B12S1U1B0(g)→ F(g)+79.0 kJ/mol 
F(g)+ eS1U1P1-S1S1P0 → FS1U1P1-S1S1P0(g) -328.0 kJ/mol 
CaS1U1P12 + 2 FS1U1P1-S1S1P0(g) → CaFS1U1B12S1U1B0(s) -2630 kJ/mol (reverse) 
Adding the above equations, we get: 
CaS1U1P12 + 1/2 FS1U1B12S1U1B0(g) → CaFS1U1B12S1U1B0(s) -1214 kJ/mol 
Therefore, the energy change for the formation of CaFS1U1B12S1U1B0(s) from its elements in their standard states is -1214 kJ/mol, which is option C.

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