Using standard enthalpies information, calculate the standard enthalpy change for this reaction:
a) (thermite reaction) 2Al(s) + Fe2O3(s) = Al2O3(s) + 2Fe(s)
b) Mg(OH)2(s) = MgO(s) + H2O(I)
c) N2O4(g) + 4H2(g) = N2(g) + 4H2O(g)
d) SiCl4(I) + 2H2O(I) = SiO2(s) + 4HCI(g)
dHrxn = (n*dHf products) - (n*dHf reactants)
To calculate the standard enthalpy change for a reaction, you can use the standard enthalpies of formation for each substance involved. The standard enthalpy change (ΔH) of a reaction can be determined using the equation:
ΔH = ΣΔHf(products) - ΣΔHf(reactants)
Where:
- ΔH is the standard enthalpy change
- ΣΔHf(products) is the sum of the standard enthalpies of formation of the products
- ΣΔHf(reactants) is the sum of the standard enthalpies of formation of the reactants
Let's calculate the standard enthalpy change for each reaction:
a) (thermite reaction)
2Al(s) + Fe2O3(s) = Al2O3(s) + 2Fe(s)
To calculate ΔH, we need the standard enthalpies of formation (ΔHf) for Al2O3(s), Fe2O3(s), and Fe(s).
ΔH = [ΔHf(Al2O3) + Σ(ΔHf(products))] - [ΔHf(Fe2O3) + Σ(ΔHf(reactants))]
b)
Mg(OH)2(s) = MgO(s) + H2O(I)
To calculate ΔH, we need the standard enthalpies of formation (ΔHf) for MgO(s), Mg(OH)2(s), and H2O(I).
ΔH = [ΔHf(MgO) + Σ(ΔHf(products))] - [ΔHf(Mg(OH)2) + Σ(ΔHf(reactants))]
c)
N2O4(g) + 4H2(g) = N2(g) + 4H2O(g)
To calculate ΔH, we need the standard enthalpies of formation (ΔHf) for N2O4(g), N2(g), H2O(g), and H2(g).
ΔH = [ΔHf(N2) + 4(ΔHf(H2O)) + Σ(ΔHf(products))] - [ΔHf(N2O4) + 4(ΔHf(H2)) + Σ(ΔHf(reactants))]
d)
SiCl4(I) + 2H2O(I) = SiO2(s) + 4HCl(g)
To calculate ΔH, we need the standard enthalpies of formation (ΔHf) for SiO2(s), SiCl4(I), H2O(I), and HCl(g).
ΔH = [ΔHf(SiO2) + 4(ΔHf(HCl)) + Σ(ΔHf(products))] - [ΔHf(SiCl4) + 2(ΔHf(H2O)) + Σ(ΔHf(reactants))]
To calculate ΔH for each reaction, you need to look up the standard enthalpies of formation for the substances involved. These values can be found in reference books or online databases. Once you have the values, substitute them into the corresponding equations above and calculate the ΔH for each reaction.