1.1. The feasibility of a chemical reaction depends on the standard Gibbs free energy change, ΔG^ɵ. This is dependent on the standard enthalpy and entropy changes, and the temperature.

State and explain whether the following processes will lead to an increase or decrease in entropy.

i) the reaction of magnesium with hydrochloric acid entropy

entropy change ....................................

explanation ..............................................

[1]

ii) the dissolving of solid potassium chloride in water

entropy change ....................................

explanation ...........................................

[1]

iii) the condensing of water from steam

entropy change ....................................

explanation .............................................

[1]

1.2. Magnesium carbonate can be decomposed on heating.

MgCO₃ (s) → MgO (s) + CO₂ (g)      ΔH^ɵ = +117 kJ mol^–1

Standard entropies are shown in Table 2.1.

Table 2.1

i) Calculate ΔG^ɵ for this reaction at 298 K.

 Show your working.  

ΔG^ɵ = ............................................. kJ mol^–1 

[3]

ii) Explain why this reaction is feasible only at high temperatures. 

[1]

1.3. Table 2.2 lists values of solubility products, K_sp, of some Group 2 carbonates.

Table 2.2

Deduce the trend in the solubility of the Group 2 carbonates down the group. Justify your answer using the data given.

1.4. i) Write an equation to show the equilibrium for the solubility product of MgCO₃. Include state symbols.

..................................... ⇌ ..................................................

[1]

 ii) With reference to your equation in (d)(i), suggest what is observed when a few cm³ of concentrated Na₂CO₃ (aq) are added to a saturated solution of MgCO₃. Explain your answer. 

[2]

1.5. Use the data in Table 2.2 to calculate the solubility of MgCO₃ in water at 298 K, in g dm^–3.

 Show your working. 

solubility of MgCO₃ = ................................................ g dm^–3

1.6. Describe and explain the variation in the thermal stabilities of the carbonates of the Group 2 elements.