calculate the change in energy expected for each of the following processes
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
To calculate the change in energy (ΔE) for each of the given processes, you need to consider the enthalpies of formation and bond energies of the involved molecules and ions.
1. Rb(g) + Br(g) → Rb+(g) + Br-(g)
To calculate the change in energy for this process, you need to find the enthalpies of formation of Rb+ and Br- ions. Look up the values for the enthalpies of formation from a reliable source such as a chemistry textbook or database. The enthalpy change (ΔH) will be the sum of the enthalpies of formation for the products (Rb+ + Br-) minus the sum of the enthalpies of formation for the reactants (Rb + Br).
2. Mg(g) + I(g) → Mg+(g) + I-(g)
Similar to the previous process, you need to find the enthalpies of formation of Mg+ and I- ions. Again, look up the values for the enthalpies of formation. Calculate ΔH by subtracting the sum of the enthalpies of formation of the reactants (Mg + I) from the sum of the enthalpies of formation of the products (Mg+ + I-).
3. Mg+(g) + I(g) → Mg+2(g) + I-(g)
For this reaction, you need to find the enthalpies of formation of Mg+2 and I- ions. Calculate ΔH by subtracting the sum of the enthalpies of formation of the reactants (Mg+ + I) from the sum of the enthalpies of formation of the products (Mg+2 + I-).
4. Mg(g) + 2I(g) → Mg+2(g) + 2I-(g)
Once again, find the enthalpies of formation for Mg+2 and I- ions. Calculate ΔH by subtracting the sum of the enthalpies of formation of the reactants (Mg + 2I) from the sum of the enthalpies of formation of the products (Mg+2 + 2I-).
Remember to multiply the enthalpy values by the appropriate stoichiometric coefficients to account for the balanced equation. The resulting values will be in kilojoules (kJ), as specified in the question.
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.