Thermodynamics
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Anhydrous magnesium chloride, MgCl2, can absorb water to form the hydrated salt MgCl2.4H2O: MgCl2 (s) + 4H2O (l) → MgCl2.4H2O (s) Suggest one reason why the enthalpy change for this reaction cannot be determined directly by calorimetry
Not possible to prevent some dissolving
A reaction is exothermic and has a negative entropy change. Explain which statement is correct and why A. The reaction is always feasible B. The reaction is feasible above a certain temperature C. The reaction is feasible below a certain temperature D. The reaction is never feasible
• ΔG = ΔH - TΔS • Remember, for reaction to be feasible ΔG must be 0 or negative • ‘Exothermic’ tells us ΔH is negative and ‘negative entropy change’ tells us S is negative, making -TΔS positive • Therefore, T cannot be too large or else it would make -TΔS more positive than ΔH is negative, making ΔG positive which makes it unfeasible. • So, C is the correct option