ammonium nitrate decomposes to N2O and water at temperatures between 250 C and 300 C. Write a balanced chemical reaction describing the decomposition of ammonium nitrate, and calculate the standard heat of reaction using the appropriate enthalpies of formation. Please include phases. Include the steps that you took
To write a balanced chemical reaction for the decomposition of ammonium nitrate (NH4NO3), we need to consider the products formed, which are nitrogen dioxide (N2O) and water (H2O). The balanced chemical reaction can be represented as follows:
NH4NO3 (s) → N2O (g) + 2 H2O (g)
In this reaction, one mole of ammonium nitrate decomposes to yield one mole of nitrogen dioxide gas and two moles of water vapor.
To calculate the standard heat of reaction (∆H°) using the appropriate enthalpies of formation (∆H°f), we can use the following expression:
∆H° = Σ∆H°f(products) - Σ∆H°f(reactants)
Now, let's calculate the standard heat of reaction by determining the enthalpies of formation of the products and reactants involved in the balanced equation.
The enthalpies of formation (∆H°f) for the given compounds are as follows:
- ∆H°f(N2O) = 81 kJ/mol
- ∆H°f(H2O, g) = -241.8 kJ/mol
- ∆H°f(NH4NO3) = -365.6 kJ/mol
Using these values, let's calculate the standard heat of reaction:
∆H° = [ (∆H°f(N2O)) + 2(∆H°f(H2O, g)) ] - (∆H°f(NH4NO3))
= [ 81 kJ/mol + 2(-241.8 kJ/mol) ] - (-365.6 kJ/mol)
= 81 kJ/mol - 483.6 kJ/mol + 365.6 kJ/mol
= -38 kJ/mol
Therefore, the standard heat of reaction (∆H°) for the decomposition of ammonium nitrate is -38 kJ/mol.
Note: The negative sign indicates that the reaction is exothermic, meaning it releases heat energy.
When writing the equation, pay special attention to what form water takes between those temperatures.
Ammonium Nitrate is
NH₄NO₃ = -365.6 kJ/mol
N20 = +81.6 kJ/mol
H20 = -241.8 kJ/mol
Must balance decomposition equation.
Then it's products - reactants.
(Answer hint: somewhere in the ballpark of -35 kJ/mol)
Aaaahh! Don't heat it to 250C. It will explode. You will form N2O slowly heating to 170C.
NH4NO3 ==>N2O + 2H2O
dHrxn = (n*dHf products) - (n*dHf reactants)