Question

Pb.8. Consider the following balanced thermochenmical equation for the decomposition of the mineral magnesite: MgCOs(s) MgO(s)+CO2(g) AHn 117.3 kJ a) Is heat absorbed or released in the reaction? b) What is AHnn for the reverse reaction? c) What is AH when 5.35 mol of CO2 reacts with excess MgO? d) What is AH when 35.5 g of CO2 reacts with excess MgO? Page 3 of 4

Answer 1

8)

a) The reaction is endothermic. This is because ΔH_rxn < 0.

b) The reverse reaction of above equation can be written as

MgO_(s) + CO_2(g) --> MgCO_3(s) ΔH_rxn = -117.3 kJ

Since, ΔH_rxn >0 for this reaction. therefore, this reaction is exothermic.

c) 5.35 mole of CO₂ react with 5.35 mole to form 5.35 mole of MgO.

Therefore, change in enthalpy = ΔH = (No. of moles of CO₂)(ΔH_rxn)

= (5.35 mole)(-117.3 kJ)

= -627.56 kJ

d) 35.5 mole of CO₂ react with 35.5 mole to form 35.5 mole of MgO.

Therefore, change in enthalpy = ΔH = (No. of moles of CO₂)(ΔH_rxn)

= (35.5 mole)(-117.3 kJ)

= -4164.15 kJ