Considering the definition of enthalpy of a chemical reaction:
(a) the heat is absorbed.
(b) ΔHrxn = -117.3 kJ.
(c) The quantity of heat released when 5.10 mol of CO₂ reacts with excess MgO is 598.23 kJ.
(d) The quantity of heat released when 41 g of CO₂ reacts with excess MgO is 109.3 kJ.
The enthalpy of a chemical reaction is defined as the heat absorbed or released in said chemical reaction when it takes place at constant pressure.
The enthalpy is an extensive property, that is, it depends on the amount of matter present.
A chemical reaction is endothermic when it absorbs energy from the surroundings. In it, the energy or enthalpy of the reactants is less than that of the products, so the enthalpy of reaction is greater than 0 or positive.
An exothermic reaction is one where energy flows out of the system. This energy is released as heat. In this case, the energy or enthalpy of reactants is greater than that of the products, so the enthalpy of reaction is less than 0 or negative.
In this case, the enthalpy of reaction is positive. Then, the heat is absorbed.
The reversed reaction is exothermic. So, the enthalpy of reaction is less than 0 or negative. Then, ΔHrxn = -117.3 kJ.
The balanced reaction is:
MgCO₃ (s) → MgO (s) + CO₂ (g)
This equation indicates that 1 mole of MgCO₃ reacts to form 1 mole of MgO and 1 mole of CO₂ and 117.3 kJ is absorbed.
For the reverse reaction, 1 mole of MgO reacts with 1 mole of CO₂ to form 1 mole of MgCO₃ and 117.3 kJ is released.
Then you can apply the following rule of three: if 1 mole of CO₂ releases 117.3 kJ of heat, 5.10 mol of CO₂ releases how much heat?
[tex]heat=\frac{5.10 moles of CO_{2}x117.3 kJ }{1mole of CO_{2}}[/tex]
heat= 598.23 kJ
Finally, the quantity of heat released when 5.10 mol of CO₂ reacts with excess MgO is 598.23 kJ.
In first place, being 44.01 g/mole the molar mass of CO₂, the amount of moles that contain 41 g is calculated as:
[tex]amount of moles= \frac{mass}{molar mass} = \frac{41 g}{44.01 \frac{g}{mole} }[/tex]
amount of moles= 0.932 moles
Then you can apply the following rule of three: if 1 mole of CO₂ releases 117.3 kJ of heat, 0.932 mol of CO₂ releases how much heat?
[tex]heat=\frac{0.932 moles of CO_{2}x117.3 kJ }{1mole of CO_{2}}[/tex]
heat= 109.3 kJ
Finally, the quantity of heat released when 41 g of CO₂ reacts with excess MgO is 109.3 kJ.
Learn more about enthalpy of a chemical reaction:
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