Exercise 10 | Ionic and Covalent Compounds

Calculate the energy of the following reaction:

Ca (g) + O (g) → CaO (g)

Is the formation of CaO exothermic or endothermic?


Data:

I1 (Ca) = 0.980 aJ

I2 (Ca) = 1.90 aJ

EA1 (O) = -0.234 aJ

EA2 (O) = 1.30 aJ

dCa-O = 240 pm

First step:

Ca (g) → Ca+ (g) + 1 e-

Ca+ (g) → Ca2+ (g) + 1 e-

Energy = I1 + I2 = 0.980 + 1.90 = 2.88 aJ


Second step:

O (g) + 1 e- → O- (g)

O- (g) + 1 e- → O2- (g)

Energy = EA1 + EA2 = 1.07 aJ


Third step:

Ca2+ (g) + O2- (g) → CaO (g)

Energy = Ecoulomb = 231 x  = -3.85 aJ


Energy of reaction: E = 2.88 + 1.07 – 3.85 = 0.10 aJ

E > 0 → The formation of CaO is endothermic