Question

Be sure to answer all parts.
Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite:

MgCO3(s) → MgO(s) + CO2(g)

Δ Hrxn = 117.3 kJ

(c) What is ΔH when 3.40 mol of CO₂ reacts with excess MgO? (kJ)

(d) What is ΔH when 31.0 g of CO₂ reacts with excess MgO? (kJ)

Answer 1

Reaction is:

MgCO₃ (s) MgO (s) + CO₂(g) H_rxn = 117.3 kJ

so, MgO (s) + CO₂(g) MgCO₃ (s) H_rxn = -117.3 kJ

(c) From reaction, 1 mol of CO₂ reacts to produce 117.3 kJ of energy

So, 3.4 mol fo CO₂ reacts to produce 398.82 kJ of energy

Thus, H_rxn = -398.82 kJ

(d) Mass of CO₂ = 31.0 g

Molar Mass of CO₂ = 44 g/mol

Moles of CO₂ =Mass of CO₂ / Molar Mass of CO₂ = 31g /(44g/mol) = 0.705 mol

So, 0.705 mol of CO₂ reacts to produce 117.3 * 0.705 mol/1 mol = 82.64 kJ of energy

Thus, H_rxn = -82.64 kJ