Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite.?

Question

Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite.
MgCO3(s) MgO(s) + CO2(g) Hrxn = 117.3 kJ

What is H when 5.30 mol CO2 reacts with excess MgO?
kJ
What is Hrxn when 34.5 g CO2 reacts with excess MgO?
kJ

Answer 1

Standard Enthalpy (H) is defined by the enthalpy change of formation for 1 mole of reactant.

If you use 5.3 moles of CO2 as the limiting reagent, you'll have 5.3 times the change in enthalpy. 5.3 X 117.3 = 621.69 kJ

With 34.5 g of CO2 as the limiting reagent, you need to start by calculating the number of moles of CO2. 1 carbon is 12g/mole. 2 O is 32 g/mol. CO2 is (12+32) 44g/mol. 34.5g divided by 44 g/mol = 0.78 moles. Therefore, you'll have less than the standard enthalpy change. You calculate the enthalpy as you did above multiple 0.78 moles by 117.3 kJ/mol = 91.49 kJ.

Answer 2

Magnesite Formula