To calculate:
The enthalpy changes of the following reactions under standard conditions using average bond energies.
a)
b)
c)
The heat of sublimation of graphite
Answer to Problem 9.92QA
Solution:
a)
b)
c)
Explanation of Solution
1) Concept:
Bond energy is the amount of energy required when one mole of bonds in the gas phase is broken. This can be used to calculate the heat of reaction (enthalpy change) by combining the
2) Formula:
3) Given:
The heat of sublimation of graphite
Bond energies from Appendix 4: Table A4.1
Bonds | Bond energy ( |
4) Calculation:
a)
Bonds | Number of bonds (mol) | Bond energy (kJ/mol) | |
|
Bonds broken | 2 | |||
1 | ||||
Bonds formed | 2 | |||
1 |
b)
Bonds | Number of bonds (mol) | Bond energy (kJ/mol) | |
|
Bonds broken | 1 | |||
1 | ||||
Bonds formed | 2 |
c)
Bonds | Number of bonds (mol) | Bond energy (kJ/mol) | |
|
Bonds broken | 2 | |||
Bonds formed | 2 |
Here, solid carbon is converted to gaseous form. Therefore, the heat of sublimation also need to be taken into consideration.
Conclusion:
The enthalpy change is the difference between the
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