(1) Use the thermodynamic values to (a) deduce the enthalpy change of each reaction (b)state if the reaction is exothermic,or endothermic,and also how much energy is released or absorbed. For thi reactions; (1) NH4NO3 (s)------>N2 (g) + 2H2O (l) (2) 4Zn (s) + 9HNO3 (aq)------->4Zn(NO3)2 (aq) + NH3 (g) 3H20 (l) (2) Predict the shift in equilibrium,if additional energy is added to the chemical reactions (1) and (2) above separately.
You have a book here.
dHrxn = (n*dHproducts) - (n*dH reactants). You can find dH for substances probably in a table in your text/notes.
If dHrxn is - it is exothermic
If dHrxn is + it is endothermic.
Adding heat to an exothermic rxn shifts it to the products.
To deduce the enthalpy change of each reaction and determine if it is exothermic or endothermic, you need to use the thermodynamic values such as standard enthalpy of formation (ΔHf) and standard enthalpy of reaction (ΔHr).
1a) NH4NO3(s) → N2(g) + 2H2O(l):
To deduce the enthalpy change for this reaction, you need to subtract the sum of the standard enthalpies of formation of the reactants from the sum of the standard enthalpies of formation of the products. The ΔHf values can be found in thermodynamic tables or online sources. The equation becomes:
ΔHr = [ΔHf(N2) + 2ΔHf(H2O)] - ΔHf(NH4NO3)
1b) To determine if the reaction is exothermic or endothermic, you can look at the sign of the enthalpy change (ΔHr).
- If ΔHr is negative (exothermic), it means the reaction releases energy.
- If ΔHr is positive (endothermic), it means the reaction absorbs energy.
2a) 4Zn(s) + 9HNO3(aq) → 4Zn(NO3)2(aq) + NH3(g) + 3H2O(l):
Using the same approach as before, you can calculate the enthalpy change for this reaction by subtracting the sum of the standard enthalpies of formation of the reactants from the sum of the standard enthalpies of formation of the products:
ΔHr = [4ΔHf(Zn(NO3)2) + ΔHf(NH3) + 3ΔHf(H2O)] - [4ΔHf(Zn) + 9ΔHf(HNO3)]
2b) Again, check the sign of ΔHr to determine if the reaction is exothermic or endothermic:
- If ΔHr is negative, the reaction is exothermic.
- If ΔHr is positive, the reaction is endothermic.
Now, let's move on to the second part of your question:
3) To predict the shift in equilibrium if additional energy is added to the reactions separately, we need to consider Le Chatelier's principle.
For reaction (1), if you add energy to the system, the equilibrium will shift towards the products (N2 and H2O) to consume the excess energy. This is because the reaction is endothermic, and by adding energy, you disrupt the balance, promoting the forward reaction.
For reaction (2), if you add energy to the system, the equilibrium will shift towards the reactants (Zn and HNO3) to dissipate the excess energy. This is because the reaction is exothermic, and by adding energy, you create a stress that is relieved by promoting the reverse reaction.
Remember, these predictions are based on the assumption that temperature is the only factor affected by the added energy. In reality, other factors such as pressure and concentration may also play a role in determining the shift in equilibrium.