Use the given data and calculate the enthalpy change for the following:
a) B2O3(s)+3COCL2(g)--->2BCL3(g)+3CO2(g)
b)Hg(l) +2Ag+(aq)--->Hg2+(aq)+2Ag(s)
compound:
B2O3(s)
COCL2(g)
BCL3(g)
CO2(g)
Ag+ (aq)
Hg2+ (aq)
Delta H (standard circle)f kj/mol
-1272.8
-218.8
-403.8
-393.5
+105.6
+171.1
a) B2O3(s)+3COCL2(g)--->2BCL3(g)+3CO2(g)
DHrxn = (sum DH products) - (sum DH reactants).
DHrxn = [(2*DH BCl3) + (3*DH CO2)] - [(DH B2O3) + (3*DH COCl2)]
To calculate the enthalpy change for the given reactions, you need to use Hess's law, which states that the enthalpy change of a reaction is the same regardless of the number of steps taken to convert the reactants to products.
Hess's law allows us to use known enthalpy changes of other reactions to determine the enthalpy change for a given reaction.
a) B2O3(s) + 3COCl2(g) ---> 2BCl3(g) + 3CO2(g)
Step 1: Decompose B2O3(s) into its elements (B and O) with the known enthalpy change of -1272.8 kJ/mol.
B2O3(s) ---> 2B(s) + 1.5O2(g) ΔH1 = -1272.8 kJ/mol
Step 2: Convert 2B(s) and 1.5O2(g) into 2BCl3(g) with the known enthalpy change of -218.8 kJ/mol.
2B(s) + 3Cl2(g) ---> 2BCl3(g) ΔH2 = -218.8 kJ/mol
Step 3: Convert 3COCl2(g) into 3CO2(g) with the known enthalpy change of -393.5 kJ/mol.
3COCl2(g) ---> 3CO2(g) + 3Cl2(g) ΔH3 = -393.5 kJ/mol
To find the enthalpy change for the overall reaction, we add all the enthalpy changes:
ΔH(total) = ΔH1 + ΔH2 + ΔH3
ΔH(total) = -1272.8 kJ/mol + (-218.8 kJ/mol) + (-393.5 kJ/mol)
b) Hg(l) + 2Ag+(aq) ---> Hg2+(aq) + 2Ag(s)
Step 1: Convert Hg(l) to Hg2+(aq) with the known enthalpy change of +105.6 kJ/mol.
Hg(l) ---> Hg2+(aq) ΔH1 = +105.6 kJ/mol
Step 2: Convert Ag+(aq) to Ag(s) with the known enthalpy change of +171.1 kJ/mol.
2Ag+(aq) + 2e- ---> 2Ag(s) ΔH2 = +171.1 kJ/mol
To find the enthalpy change for the overall reaction, we add both enthalpy changes:
ΔH(total) = ΔH1 + ΔH2
ΔH(total) = +105.6 kJ/mol + (+171.1 kJ/mol)
By summing up the individual enthalpy changes involved in each step of the reactions, you can calculate the enthalpy change for the given reactions using the known enthalpy changes provided.