Calculate the heat of combustion:
1.C2H4(g)+3O2(g)===>2CO2(g)+2h20(L)
_____kJ/mol
2.2H2S(g)+3O2(g)===>2H2O(L)+2SO2(g)
_____kJ/mol
Look up delta Hof for CO2 and H2O (and multily each by 2).
delta H rxn = (sum products)-(sum reactants).
To calculate the heat of combustion for each reaction, we need to use the bond dissociation energies (BDE) of the bonds involved. Here are the calculations for each reaction:
1. C2H4(g) + 3O2(g) => 2CO2(g) + 2H2O(L)
First, let's calculate the bonds broken:
- In C2H4, there are 5 C-H bonds. The average BDE for a C-H bond is approximately 413 kJ/mol, so the energy required to break the C-H bonds is 5 * 413 = 2065 kJ/mol.
- In O2, there are 3 O=O bonds. The BDE for an O=O bond is approximately 496 kJ/mol, so the energy required to break the O=O bonds is 3 * 496 = 1488 kJ/mol.
Next, let's calculate the bonds formed:
- In CO2, there are 4 C=O bonds. The average BDE for a C=O bond is approximately 799 kJ/mol, so the energy released in forming the C=O bonds is 4 * 799 = 3196 kJ/mol.
- In H2O, there are 2 O-H bonds. The average BDE for an O-H bond is approximately 464 kJ/mol, so the energy released in forming the O-H bonds is 2 * 464 = 928 kJ/mol.
Now, let's calculate the net energy change:
Net energy change = (energy required to break bonds) - (energy released in forming bonds)
= (2065 kJ/mol + 1488 kJ/mol) - (3196 kJ/mol + 928 kJ/mol)
= -571 kJ/mol
Therefore, the heat of combustion for the reaction C2H4(g) + 3O2(g) => 2CO2(g) + 2H2O(L) is -571 kJ/mol.
2. 2H2S(g) + 3O2(g) => 2H2O(L) + 2SO2(g)
Similarly, let's calculate the bonds broken:
- In H2S, there are 4 H-S bonds. The average BDE for an H-S bond is approximately 339 kJ/mol, so the energy required to break the H-S bonds is 4 * 339 = 1356 kJ/mol.
- In O2, there are 3 O=O bonds. The BDE for an O=O bond is approximately 496 kJ/mol, so the energy required to break the O=O bonds is 3 * 496 = 1488 kJ/mol.
Next, let's calculate the bonds formed:
- In H2O, there are 2 O-H bonds. The average BDE for an O-H bond is approximately 464 kJ/mol, so the energy released in forming the O-H bonds is 2 * 464 = 928 kJ/mol.
- In SO2, there are 2 S=O double bonds. The average BDE for an S=O double bond is approximately 525 kJ/mol, so the energy released in forming the S=O bonds is 2 * 525 = 1050 kJ/mol.
Now, let's calculate the net energy change:
Net energy change = (energy required to break bonds) - (energy released in forming bonds)
= (1356 kJ/mol + 1488 kJ/mol) - (928 kJ/mol + 1050 kJ/mol)
= 866 kJ/mol
Therefore, the heat of combustion for the reaction 2H2S(g) + 3O2(g) => 2H2O(L) + 2SO2(g) is 866 kJ/mol.
To calculate the heat of combustion for each reaction, you need to use bond energies and enthalpy of formation values. Here's how to do it step by step:
1. C2H4(g) + 3O2(g) ==> 2CO2(g) + 2H2O(L)
a) Determine the bonds broken in the reactants:
- In C2H4, there are 5 C-H bonds (5 x bond energy of C-H)
- In O2, there is a double bond (1 x bond energy of O=O)
- Therefore, the total energy required to break the bonds in the reactants is equal to (5 x bond energy of C-H) + (1 x bond energy of O=O).
b) Determine the bonds formed in the products:
- In CO2, there are 4 C=O bonds (4 x bond energy of C=O)
- In H2O, there are 2 O-H bonds (2 x bond energy of O-H)
- Therefore, the total energy released when forming the bonds in the products is equal to (4 x bond energy of C=O) + (2 x bond energy of O-H).
c) Calculate the overall energy change:
- The heat of combustion is the difference between the energy required to break the bonds in the reactants and the energy released when forming the bonds in the products.
- So, calculate the difference: (Total energy required to break bonds) - (Total energy released when forming bonds).
2. 2H2S(g) + 3O2(g) ==> 2H2O(L) + 2SO2(g)
a) Determine the bonds broken in the reactants:
- In H2S, there are 2 H-S bonds (2 x bond energy of H-S)
- In O2, there is a double bond (1 x bond energy of O=O)
- Therefore, the total energy required to break the bonds in the reactants is equal to (2 x bond energy of H-S) + (1 x bond energy of O=O).
b) Determine the bonds formed in the products:
- In H2O, there are 2 O-H bonds (2 x bond energy of O-H)
- In SO2, there is a double bond and a single bond (1 x bond energy of S=O + 1 x bond energy of O-S)
- Therefore, the total energy released when forming the bonds in the products is equal to (2 x bond energy of O-H) + (1 x bond energy of S=O) + (1 x bond energy of O-S).
c) Calculate the overall energy change:
- The heat of combustion is the difference between the energy required to break the bonds in the reactants and the energy released when forming the bonds in the products.
- So, calculate the difference: (Total energy required to break bonds) - (Total energy released when forming bonds).
Note: You will need to use bond energy values and enthalpy of formation values, which can be found in reference books or online databases.