Use bond energies to predict the molar enthalpy of combustion of acetylene gas.
2C2H2 + 5O2--> 4CO2 + 2H2O
I am confused as to how to do the 2C2H2 in relation to the bonds?
how many c-c bonds would there be, or would they be triple bonds?
The way I read it you break 4 C-H bonds, 1 CtriplebondC bond and 1 O-0 bond (on the reactant side) and form 8 C=O bonds, and 4 O-H bonds on the product side.
To calculate the molar enthalpy of combustion of acetylene gas, you can use the concept of bond energies. Bond energies represent the amount of energy required to break a specific type of bond.
In the case of acetylene (C2H2), each carbon atom is bonded to another carbon atom by a triple bond. So, there are two triple bonds (C≡C) present in acetylene.
To calculate the molar enthalpy of combustion, you need to consider the bonds broken and formed during the reaction. In the balanced equation you provided:
2C2H2 + 5O2 → 4CO2 + 2H2O
The reactants, acetylene (C2H2) and oxygen (O2), are being oxidized to form carbon dioxide (CO2) and water (H2O), respectively.
As you correctly mentioned, there are two triple bonds in acetylene (2C2H2). To break these bonds, you need to supply energy. The average bond energy for a carbon-carbon triple bond is around 825 kJ/mol.
So, to break the two triple bonds in acetylene, you would require a total of 2 * 825 kJ/mol = 1650 kJ/mol.
Once the bonds are broken, new bonds are formed. In the products, you have four carbon dioxide (CO2) molecules, each containing two double bonds (C=O). The average bond energy for a carbon-oxygen double bond is approximately 740 kJ/mol.
Therefore, to form the carbon dioxide molecules, you would release a total of 4 * 2 * 740 kJ/mol = 5920 kJ/mol.
And finally, you have two water (H2O) molecules formed, each with a single oxygen-hydrogen bond (O-H). The average bond energy for an oxygen-hydrogen bond is about 460 kJ/mol.
So, to form the water molecules, you would release a total of 2 * 1 * 460 kJ/mol = 920 kJ/mol.
To calculate the molar enthalpy of combustion, you need to subtract the energy required to break the bonds from the energy released when the new bonds are formed:
Molar enthalpy of combustion = Total bond energy broken - Total bond energy formed
Molar enthalpy of combustion = (1650 kJ/mol) - [(5920 kJ/mol) + (920 kJ/mol)]
Molar enthalpy of combustion = -4350 kJ/mol
Therefore, the molar enthalpy of combustion of acetylene gas is -4350 kJ/mol.
Note: The negative sign indicates that the reaction is exothermic, meaning it releases heat energy.
In acetylene gas (C2H2), each carbon atom is bonded to another carbon atom with a triple bond. Therefore, there are two C-C triple bonds in acetylene.
To determine the molar enthalpy of combustion of acetylene gas using bond energies, you need to analyze the bonds involved in the reaction.
The bond energies (also known as bond dissociation energies) represent the energy required to break a specific type of bond. In this case, you need to refer to the bond energies for all the bonds broken and formed during the combustion reaction.
The bond energies needed for the calculation are as follows:
- C-C triple bond: 839 kJ/mol (energy required to break one C-C triple bond)
- O=O double bond: 497 kJ/mol (energy required to break one O=O double bond)
- C=O double bond: 743 kJ/mol (energy required to break one C=O double bond)
- O-H single bond: 463 kJ/mol (energy required to break one O-H single bond)
For the reaction 2C2H2 + 5O2 → 4CO2 + 2H2O, you can use the bond energies to calculate the enthalpy of combustion.
First, calculate the total energy required to break the bonds in the reactants (2C2H2 and 5O2), and then subtract the total energy released by forming the bonds in the products (4CO2 and 2H2O).
Total energy required to break the bonds in the reactants:
2C2H2 = 2 * (2 C-C triple bonds) = 2 * 2 * 839 kJ/mol
5O2 = 5 * (1 O=O double bond) = 5 * 1 * 497 kJ/mol
Total energy released by forming the bonds in the products:
4CO2 = 4 * (2 C=O double bonds) = 4 * 2 * 743 kJ/mol
2H2O = 2 * (1 O-H single bond) = 2 * 1 * 463 kJ/mol
Now, calculate the total energy change:
Total energy change = (Total energy required to break bonds in reactants) - (Total energy released by forming bonds in products)
Total energy change = (2 * 2 * 839 kJ/mol + 5 * 1 * 497 kJ/mol) - (4 * 2 * 743 kJ/mol + 2 * 1 * 463 kJ/mol)
By calculating the above equation, you will get the molar enthalpy of combustion of acetylene gas.