COMBUSTION of PROPANE
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COMBUSTION of PROPANE. 1.What does the reaction involve? (reactants and products). Reaction needs to be balanced. COMBUSTION of PROPANE. 2. Envision the “structural formulas” for the reactants and the products (from your knowledge of Lewis structures). COMBUSTION of PROPANE.

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COMBUSTION of PROPANE

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Combustion of propane

COMBUSTION of PROPANE

1.What does the reaction involve? (reactants and products)

Reaction needs to be balanced


Combustion of propane

COMBUSTION of PROPANE

2.Envision the “structural formulas” for the reactants and the products (from your knowledge of Lewis structures)


Combustion of propane

COMBUSTION of PROPANE

3.List the bonds broken (between which atoms)

bonds within the reactants are expected to be broken

In C3H8 2 x C-C bonds

8 x C-H bonds

In O2 1 x O=O bond


Combustion of propane

COMBUSTION of PROPANE

The numbers and types of bonds within the reactants which are expected to be broken are…

In C3H8 2 x C-C bonds

8 x C-H bonds

In O2 1 x O=O bond

However, we need to check the coefficient in front of each reactant (look at the balanced equation)

There are 5 moles of O2 reacting with each mole of propane

Therefore,

in 5 x O2 5 x O=O bonds


Combustion of propane

COMBUSTION of PROPANE

4.Find the Bond Dissociation Energies (BDE) associated for each bond (from Table 4.4)

BDE’s for

C-C bonds: 356 kJ/mole

C-H bonds: 436 kJ/mole

O=O bonds: 498 kJ/mole


Combustion of propane

COMBUSTION of PROPANE

Remember, there are

2 x C-C bonds

8 x C-H bonds

5 x O=O bonds (after balancing the equation)

Here is the energy required to break all the bonds mentioned above:

2 x 356 kJ/mole = 712 kJ

8 x 436 kJ/mole = 3488 kJ

5 x 498 kJ/mole = 2490 kJ

TOTAL: 6690 kJ


Combustion of propane

COMBUSTION of PROPANE

5.We now need to look at the products and the new bonds formed as a result of the reaction

These are the new bonds which are formed


Combustion of propane

COMBUSTION of PROPANE

new bonds formed within the products

In CO2 2 x C=O bonds

In H2O2 x O-H bonds

However, we need to check the coefficient in front of each reactant (look at the balanced equation)

There are 3 moles of CO2 being formed (for each mole of propane)

and 4 moles of H2O

therefore

In 3 x CO23 x 2 x C=O bonds

In 4 x H2O 4x 2 x O-H bonds


Combustion of propane

COMBUSTION of PROPANE

  • 6.Find the Bond Dissociation Energies (BDE) associated for each bond being formed

  • (from Table 4.4)

  • BDE’s for

    C=O bonds: 803 kJ/mole

    O-H bonds: 467 kJ/mole


    Combustion of propane

    COMBUSTION of PROPANE

    Remember, there are

    3 x 2 x C=O bonds

    4 x 2 x O-H bonds

    being formed (after balancing the equation)

    Here is the energy released when all the bonds mentioned above are formed:

    6 x 803 kJ/mole = 4818 kJ

    8 x 467 kJ/mole = 3736 kJ

    TOTAL: 8554 kJ


    Combustion of propane

    COMBUSTION of PROPANE

    7.Subtract the total energy released from the total energy required to break the bonds to determine the heat of reaction, DH

    DH = 8554 kJ - 6690 kJ

    =1864 kJ

    Let’s focus on the units now:

    This is 1864 kJ per mole of propane, C3H8 undergoing complete combustion


    Combustion of propane

    COMBUSTION of PROPANE

    8.What if we wishto determine the heat of reaction, DH, per gram of propane, C3H8 undergoing complete combustion

    In 1 mole of C3H8 there are 44 g of C3H8

    Therefore, the DH value we calculated previously is associated with 44 g of C3H8

    DH = 1864 kJ per 44 g of propane undergoing complete combustion


    Combustion of propane

    COMBUSTION of PROPANE

    If 44 g of C3H8 releases 1864 kJ of energy,

    then 1.0 g of C3H8 will release 1/44 of that amount

    DH = 1864/44 kJ per 1.0 g of propane = 42.4 kJ/g of propane

    viewing the following units together

    might further clarify the type of calculation involved in converting the amount of energy from per mole to per gram


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