calculate the change in energy expected for each of the following processes

Question

1. Rb(g) + Br(g) --> Rb+ (g) + Br- (g)

2. Mg(g) + I(g) --> Mg+ (g) + I- (g)

3. Mg+ (g) + I(g) -> Mg+2 (g) + I- (g)

4. Mg(g) + 2I (g) -> Mg+2 (g) + 2I- (g)

in kJ

Answer 1

For #1, you want the to add the two following:
Rb(g) ==> Rb^+(gas) + e I.P. (Ionization potential). This will be a positive number.
Br(g)+ e =>Br^-(g) +E.A. (electron affinity) This will be a negative number.

The others are done the same way. In the case of #2, you are removing only 1 electron from Mg(g); therefore, you want only I.P. #1 and not #2.