Standard Enthalpy and Entropy of Reactions - College Chemistry
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Use average bond enthalpies to estimate the enthalpy change, in kilojoules, of the combustion of one mole of hexane 
to form liquid water and carbon dioxide gas.
Type of Bond Average bond enthalpy 
Carbon-hydrogen single bond 414 Carbon-oxygen double bond 736 Oxygen-oxygen double bond 498 Oxygen-hydrogen single bond 464 Carbon-carbon single bond 347
Use average bond enthalpies to estimate the enthalpy change, in kilojoules, of the combustion of one mole of hexane
| Type of Bond | Average bond enthalpy |
|---|---|
| Carbon-hydrogen single bond | 414 |
| Carbon-oxygen double bond | 736 |
| Oxygen-oxygen double bond | 498 |
| Oxygen-hydrogen single bond | 464 |
| Carbon-carbon single bond | 347 |
Start by writing the balanced equation for the combustion of hexane:
Recall the following equation:
Remember that energy is required to break bonds, so 
should be positive. Energy is also released when bonds are made so 
should be negative.
Next, draw out the Lewis structures of each molecule to figure out the number of bonds made or broken.
For the hexane, there are 
bonds that must be broken, and 
bonds that must be broken.
For each oxygen, there is only 1 oxygen double bond to break. However, we will need to multiply this number by its stoichiometric coefficient.
For each carbon dioxide, there are 
double bonds between carbon and oxygen to break. For the given equation, there are 
total of these double bonds because we have 
moles of carbon dioxide.
For each water, there are 
single bonds between hydrogen and oxygen. For the given equation, there are a total of 
of these bonds because we have 
moles of water.
Now, use the given information regarding to average bond enthalpies to find the change in enthalpy for the reaction.
Start by writing the balanced equation for the combustion of hexane:
Recall the following equation:
Remember that energy is required to break bonds, so
Next, draw out the Lewis structures of each molecule to figure out the number of bonds made or broken.
For the hexane, there are
For each oxygen, there is only 1 oxygen double bond to break. However, we will need to multiply this number by its stoichiometric coefficient.
For each carbon dioxide, there are
For each water, there are
Now, use the given information regarding to average bond enthalpies to find the change in enthalpy for the reaction.
Compare your answer with the correct one above