Question

Lab 6 Thermodynamics

1. Write the chemical equation representing the net ionic equation for the precipitation of AgCl resulting from mixing a solution containing Ag⁺ with a solution containing Cl^-.

2. Write the chemical equation corresponding to the formation of 1 mol of AgCl from its element in their standard states. This is the equation for ∆G°_f298 for AgCl. (Refer to your thermochemistry chapter for the topic of formation equations.)

3. How do the two equations (in the two previous questions) differ? Briefly explain the difference in their ∆G° calculation.

4. The value of ∆G°_{f 298} for Mg²⁺ is –454.8 kJ/mol. The value of ∆G°_{f 298} for MgCl₂·6H₂O is -2114.64 kJ/mol.

a. Use these values as well as other thermodynamic data available on the chart supplied in this lab to calculate the free energy change for the reaction under standard conditions, ∆G°_rxn.

b. Calculate the free energy change for the reaction ∆G _rxn when equal volumes of 0.20 M Mg²⁺ and 0.20 M Cl^- are mixed.

c. Based on your calculations, predict whether or not a precipitate will form.

Lab 6 Thermodynamics REPORT SHEETS DATA    Table 1

Salt/ppt equation Sample equation provided for first entry only		∆G°rxn (kJ)	∆Grxn (kJ) (hint: Q ≠ 1)	Predict whether precipitation will occur
AgCl Ag+(aq) + Cl-(aq) → AgCl(s)
AgI
Ag2SO4
BaCl2∙2H2O
Ba(NO3)2
BaSO4
Na2SO4∙10H2O
CaCl2
CaSO4∙2H2O
PbCl2	273K
PbCl2	298K
PbCl2	373K
Ba(NO3)2	273K
Ba(NO3)2	298K
Ba(NO3)2	373K

Answer 1

1. Ag+ (aq)+ Cl- (aq) = AgCl (s)

2. Ag (s) + 1/2 Cl2 (g) = AgCl (s)

The complete Born-Haber cycle is as follows: 3. The first equation corresponds to the lattice energy of AgCl and hydration energy of ions only. But the second one is relatied with more parameters (like fusion enthalpy, ionisation energy, electron affinity ) as the conversion comes from the standard state. So, the the difference is lot from thermodynamic aspects.