Enthelpy changes Using Hess' law

  • Thread starter Andy21
  • Start date
  • Tags
    Law
This is because the net change in enthalpy remains the same regardless of the number of moles involved in the reaction. In summary, according to Hess's law, the enthalpy change is a state function and is not affected by the number of moles in a reaction, therefore the enthalpy change of reaction 1 does not have to be doubled when calculating the enthalpy change for the reaction of 2 moles of NaHCO3 with H2SO4.
  • #1
Andy21
20
0

Homework Statement


When using Hess' law to calculate the enthalpy change for the thermal decomposition of sodium hydrogen carbonate, why doesn't the enthalpy change of the reaction of one mole of NaHCO3 with H2SO4 (reaction 1) have to be doubled when you calculate the reaction of 2 moles of NaHCO3 with H2SO4 to produce Na2SO4 + 2CO2 + 2H2O.


Homework Equations


Reaction of the thermal decomposition-2NaHCO3->Na2CO3 + CO2 + H20
Reaction 1- 2NaHCO3 + H2SO4->Na2SO4 + 2CO2 + 2H2O


The Attempt at a Solution

 
Physics news on Phys.org
  • #2
Hess's law states that the enthalpy change of a reaction is independent of the route by which it takes place. Therefore, the enthalpy change for reaction 1 does not have to be doubled in order to calculate the enthalpy change of the reaction of 2 moles of NaHCO3 with H2SO4.
 

1. What is Hess' law and how is it used to calculate enthalpy changes?

Hess' law is a thermodynamic principle that states the overall enthalpy change of a chemical reaction is independent of the pathway taken. This means that the initial and final states of a reaction will have the same enthalpy change, regardless of the intermediate steps. This law is used to calculate enthalpy changes by breaking down a reaction into smaller, known reactions and then adding or subtracting their enthalpy changes to find the overall change.

2. Can Hess' law be applied to both exothermic and endothermic reactions?

Yes, Hess' law can be applied to both exothermic and endothermic reactions. This is because the law is based on the principle of energy conservation, which states that energy cannot be created or destroyed, only transferred. Therefore, the total energy change of a reaction will remain the same regardless of the direction of the reaction.

3. How do you determine the enthalpy change of a reaction using Hess' law?

To determine the enthalpy change of a reaction using Hess' law, you need to first identify and write out the known reactions that can be used to create the overall reaction. Then, you need to calculate the enthalpy change of each of these known reactions and use them to find the overall enthalpy change by adding or subtracting them according to the stoichiometric coefficients in the overall reaction.

4. Is Hess' law always accurate in predicting enthalpy changes?

Hess' law is based on the assumption that the enthalpy change of a reaction is independent of the pathway taken. While this is mostly true, there can be small variations due to factors such as temperature, pressure, and concentration. Therefore, Hess' law may not always be 100% accurate in predicting enthalpy changes, but it is a reliable method for calculating approximate values.

5. What are some limitations of using Hess' law to calculate enthalpy changes?

One limitation of using Hess' law is that it requires knowing the enthalpy changes of the individual reactions used in the calculation. These values may not always be readily available or may be difficult to determine experimentally. Another limitation is that Hess' law assumes ideal conditions and does not take into account factors such as changes in temperature or pressure, which can affect the enthalpy change of a reaction.

Similar threads

Chemistry Valence Bond Theory: Energy of a system with H and Cl atoms
    • Biology and Chemistry Homework Help
Replies
6
Views
2K
Does sodium bicarbonate solution release CO2 when heated?
    • Biology and Chemistry Homework Help
Replies
2
Views
3K
Double titration and law of equivalence
    • Biology and Chemistry Homework Help
Replies
10
Views
2K
Is this correct Hess' law, thermodynamics
    • Biology and Chemistry Homework Help
Replies
22
Views
3K
Help with enthelpy change and Hess's Law
    • Biology and Chemistry Homework Help
Replies
1
Views
4K
Calculating Molar Enthalpy of C2H4 Combustion w/ Hess's Law
    • Biology and Chemistry Homework Help
Replies
3
Views
9K
Hess's Law Explained | Simple Explanation for Enthalpy Change
    • Biology and Chemistry Homework Help
Replies
2
Views
2K
Enthelpy change of a neutralisation reaction
    • Biology and Chemistry Homework Help
Replies
3
Views
2K
Calculating ΔH Using Hess's Law for FeO(s)CO(g) Reaction
    • Biology and Chemistry Homework Help
Replies
4
Views
2K
Calculating Energy Released by Sodium Reacting with Water
    • Chemistry
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top