How Do You Calculate Activation Energy and Heat of Reaction?

[ChemRookie]

For the reaction

CO + NO2 ----> CO2 + NO the activation energy for the forward reaction is 135kj/mol of CO reacted.

a) determine the heat of reaction
b) from the data given, and the deltaHr for the reaction, determine the activation energy for the reverse reaction
c) draw and label a potential energy diagram

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to do this question, someone said I need the standard enthalpy of formations but I can't find it anywhere in my book. Does anyone have a chart of it?

Thanks

 

[GCT]

I've seen this question one too many times at PF

You won't find the particular standard enthalpy of formation for the reaction, you'll have to deduce it. Should be supereasy. You'll need it for part a).

also activation forward-dH=activation reverse

Your text should explain how to do part c)

 

[thepatientmental]

for your question! The standard enthalpy of formation for CO, CO2, and NO2 can be found in various sources, including chemistry textbooks and online databases. Here is a table with the standard enthalpies of formation for these compounds:

Compound | Standard Enthalpy of Formation (kJ/mol)
CO | -110.5
CO2 | -393.5
NO2 | +33.2

a) To determine the heat of reaction, we first need to calculate the change in enthalpy for the reaction. This can be done by subtracting the sum of the standard enthalpies of formation for the products from the sum of the standard enthalpies of formation for the reactants. In this case, the heat of reaction would be:

ΔHrxn = [(-110.5 kJ/mol) + (+33.2 kJ/mol)] - [(-393.5 kJ/mol) + (0 kJ/mol)]
= -470.8 kJ/mol

b) To determine the activation energy for the reverse reaction, we can use the relationship between activation energy and the change in enthalpy (ΔHrxn). The activation energy for the reverse reaction would be equal to the activation energy for the forward reaction (135 kJ/mol) plus the change in enthalpy (-470.8 kJ/mol). Therefore, the activation energy for the reverse reaction would be:

Ea(reverse) = 135 kJ/mol + (-470.8 kJ/mol)
= -335.8 kJ/mol

c) A potential energy diagram shows the energy changes that occur during a chemical reaction. The x-axis represents the progress of the reaction, while the y-axis represents the potential energy of the system. The diagram would look something like this:


Potential Energy
|
|
|
|
|
|___________ Progress of Reaction
Reactants Products

The activation energy for the forward reaction (135 kJ/mol) would be shown as a peak on the energy curve, while the activation energy for the reverse reaction (-335.8 kJ/mol) would be shown as a dip. The overall change in enthalpy for the reaction (-470.8 kJ/mol) would be represented by the difference in energy between the reactants and products. The standard enthalpy of formation for each compound can also be shown on the energy