Calculating ΔH Using Hess's Law for FeO(s)CO(g) Reaction

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In summary, Hess's Law can be used to calculate the change in enthalpy (ΔH) for the reaction between solid FeO and gaseous CO. This involves breaking down the overall reaction into a series of smaller reactions, for which the enthalpy changes can be measured or calculated. The overall ΔH can then be determined by adding the individual ΔH values of the smaller reactions together. This method is useful for predicting the energy changes in complex reactions and can be applied to various chemical systems.
  • #1
Specter

Homework Statement


Using Hess's law, calculate the ΔH value for the following reaction:
FeO(s)CO(g)→Fe(s)+CO2(g)

Use these three reactions:
1. Fe2O3(s)+3CO(g)→2Fe3O4(s)+CO2(g) ΔH= -25.0 kJ

2. 3Fe2O3(s)+CO(g)→2Fe3O4(s)+CO2(g) ΔH= -47.0 kJ

3. Fe3O4(s)+CO(g)→3FeO(s)+CO2
ΔH= +38.0 kJ

Homework Equations

The Attempt at a Solution



This is what I have done so far:

Reversed reaction 3
3FeO(s)+CO2→Fe3O4(s)+CO(g) ΔH = -38.0 kJ

I've tried some other things but each time I get the incorrect answer. The examples that I was shown were way easier than this.

I'm not really sure what to do next. I reversed reaction 3 to get FeO on the left side. Any help on the steps I should take to complete this would be great... I find this question very confusing.
 
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  • #2
Your first step is definitely a correct one.

Hard to comment on your attempts (and why they yielded incorrect answers) not seeing them.

As there is an obvious mistake in the problem wording (first equation is not balanced, neither of the 1st and 2nd equation contains FeO(s), and there is no Fe(s) present anywhere) it is also impossible to point you in the right direction.

Note: state symbols (s), (aq), (g) and (l) should be not written as subscripts. It is a common error, present even in textbooks, but IUPAC defined them to be written with normal characters.
 
  • #3
Hi,

If I were you, I would try the following:

Call ΔΗformation of each substance x (ΔΗf, Fe3O4), y (ΔΗf, CO2), z (ΔΗf,Fe2O3), v (ΔΗf, CO), k (ΔΗf, FeO). Then I would form 3 equations with 5 unknown variables.

In order to find the unknown ΔΗ, I would search to find the value of (y-k-v). Perhaps, this is not impossible, since you relate the 3 unknown variables in a 3x5 system.Then, ΔΗunknown=y+ΔΗFe-k-v (ΔΗFe is considered given data-you can find it from the web).

This way, I would transform the chemical problem into a mathematical problem, but still I don't know if it is possible/easy/difficult to find the value of (y-k-v).

Edit Note : I agree with Post #2. There are problems with the equations that will make it impossible to solve the problem.
 
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  • #4
Borek said:
Your first step is definitely a correct one.

Hard to comment on your attempts (and why they yielded incorrect answers) not seeing them.

As there is an obvious mistake in the problem wording (first equation is not balanced, neither of the 1st and 2nd equation contains FeO(s), and there is no Fe(s) present anywhere) it is also impossible to point you in the right direction.

Note: state symbols (s), (aq), (g) and (l) should be not written as subscripts. It is a common error, present even in textbooks, but IUPAC defined them to be written with normal characters.

I did write it wrong, sorry about that. Is there any way I can have this thread deleted so that I can create a new one with the correct information? Also, thanks for letting me know about state symbols, in my lesson they are written as subscripts but I will write them as normal characters from now on.
 
  • #5
Specter said:
Is there any way I can have this thread deleted so that I can create a new one with the correct information?

Post the correct information and we will edit the original post, marking things that were modified.
 

1. How is ΔH calculated using Hess's Law for the FeO(s)CO(g) reaction?

The enthalpy change (ΔH) for the FeO(s)CO(g) reaction can be calculated by using the enthalpy changes of the individual steps involved in the reaction, as described by Hess's Law. This means taking into account the enthalpy changes of any intermediates or reactions that occur before the final reaction. The sum of these enthalpy changes will give the overall ΔH for the FeO(s)CO(g) reaction.

2. What is Hess's Law and how does it relate to calculating ΔH?

Hess's Law states that the enthalpy change of a reaction is independent of the pathway taken from reactants to products. This means that if a reaction can be broken down into smaller steps, the overall enthalpy change will be the sum of the enthalpy changes for each individual step. This is useful for calculating ΔH for reactions that cannot be directly measured in a laboratory.

3. Can Hess's Law be used for any reaction?

Hess's Law can be used for any reaction as long as the steps involved can be accurately measured or calculated. However, it is most useful for reactions that involve multiple steps or intermediates that cannot be directly measured.

4. How does the state of a substance affect its enthalpy change in the FeO(s)CO(g) reaction?

The state of a substance, such as solid, liquid, or gas, can affect its enthalpy change in the FeO(s)CO(g) reaction. This is because different states have different enthalpies of formation, which is the enthalpy change that occurs when one mole of a substance is formed from its elements in their standard states. Therefore, the enthalpy change for a reaction may vary depending on the state of the substances involved.

5. Can Hess's Law be used to predict the feasibility of a reaction?

No, Hess's Law cannot be used to predict the feasibility of a reaction. It only helps in calculating the enthalpy change for a reaction, but does not provide information about the rate or extent of the reaction. Other factors, such as the activation energy and equilibrium constant, must be considered to determine the feasibility of a reaction.

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