Calculating the Heat of Combustion for C2H6 Using Hess's Law

In summary, to calculate the heat of combustion for C2H6, you can use Hess's law and manipulate the given equations to create the desired equation. However, there may be a typo in the given equation and it is important to double check for accuracy.
  • #1
123456
Calculate the heat of combustion for C2H6 from the following information:
C2H4 + 3 CO2 --> 2 CO2 + 2 H2O /\H f -1409.5 kJ
C2H4 + H2 --> C2H2 /\H f - 136.7 kJ
H2 + 1/2 O2 --> H2O /\H f - 285.5 kJ


i saw someone else ask this question and they were referred to look at Hess's law.. i have done that but i am still unable to solve this i am so stuck.
could someone walk through the steps please?
 
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  • #2
C2H4 + H2 --> C2H2 /\H f - 136.7 kJ
C2H4 + 3 CO2 --> 2 CO2 + 2 H2O /\H f -1409.5 kJ

these makes no sense(they are not balanced eqs)...did you mean for the product to be C2H6 in the 2nd eq.?
 
  • #3
hmm

no, what i wrote was exactly how its written in the book... is it not able to be solved, possibly they made a typo in the book?
 
  • #4
This C2H4 + H2 --> C2H2 does not make sense.

Try C2H4 + H2 --> C2H6 perhaps. If this is in the book, there is a probably a typo.
 
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  • #5
I see, must be a typo...

Ohhh I see what you mean now, when you said it doesn't balance. It must be a typo then. Is there a formula or anything you use to calculate heat of combustion.. or is it just knowledge...?
 
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  • #6
play around w/ the equations like a puzzle and treat them like math equations. if two of the same things appear on the left and right side of the arrow you can cancel them out. use those equations to come up w/ the equation for C6H6+O2-->CO2 +O2 (i'm too lazy to balance). Remember, if you flip an equation around you change teh sign of the Enthalpy of the rxn...
 

FAQ: Calculating the Heat of Combustion for C2H6 Using Hess's Law

What is Hess's Law?

Hess's Law states that the total enthalpy change of a chemical reaction is independent of the pathway taken to get from reactants to products.

How is Hess's Law used to calculate the heat of combustion for C2H6?

Hess's Law is used by breaking down the overall reaction into a series of smaller reactions that have known enthalpy values. These smaller reactions are then combined to give the overall reaction and the corresponding enthalpy change.

What are the steps for calculating the heat of combustion for C2H6 using Hess's Law?

The steps for calculating the heat of combustion for C2H6 using Hess's Law are as follows:
1. Write out the balanced chemical equation for the combustion of C2H6.
2. Break down the overall reaction into smaller reactions that have known enthalpy values.
3. Combine the smaller reactions to give the overall reaction and the corresponding enthalpy change.
4. Use the equation Q = mcΔT to calculate the heat released during the reaction, where Q is the heat released, m is the mass of C2H6, and ΔT is the change in temperature.
5. Convert the heat released to kJ/mol by dividing by the number of moles of C2H6 in the reaction.

What are the units for the heat of combustion of C2H6?

The units for the heat of combustion of C2H6 are kJ/mol.

Why is it important to calculate the heat of combustion for C2H6?

Calculating the heat of combustion for C2H6 is important because it gives us information about the energy released when C2H6 is burned. This information is useful in understanding the thermodynamics of the reaction and can also be used for practical applications such as determining the efficiency of fuel sources.

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