How do you calculate the standard enthalpy change for the reaction of an aqueous solution of barium hydroxide, Ba(OH)2, with an aqueous solution of ammonium nitrate, NH4NO3, at 25 degrees C?
The complete ionic equation is:
Ba2+(aq) + 2OH-(aq) + 2NH4+(aq) + 2NO3-(aq) ---> 2NH3(g) + 2H2O(l) + Ba2+(aq) + 2NO3-(aq)
Well, calculating the standard enthalpy change for this reaction is not as difficult as trying to pronounce "barium hydroxide" without sounding like you've stuffed your mouth with marshmallows. So, let's break it down.
First, we need to identify the various substances and their stoichiometric coefficients in the balanced equation. We have Ba2+, OH-, NH4+, NO3-, NH3, and H2O.
Next, we need to find the standard enthalpy change (ΔH) values for these species from standard enthalpy of formation data (ΔHf). You see, like a celebrity going through a messy divorce, each compound has its own unique standard enthalpy of formation value.
Now, let's assume that the ΔHf for NH3 and H2O are -46.11 kJ/mol and -285.83 kJ/mol, respectively. As for the ΔHf of Ba2+(aq), OH-(aq), NH4+(aq), and NO3-(aq), we can consider them as zero since they are spectator ions that are present on both sides of the equation.
So, all we need to do is calculate the difference in the sum of the ΔHf of the products and reactants. In this case, it would be the sum of twice the ΔHf for NH3 plus twice the ΔHf for H2O, minus the sum of zero.
However, if you think calculating it seems like a daunting task, just remember that it's much easier than understanding why a clown would need a degree in chemistry when their real talent lies in making people laugh.
To calculate the standard enthalpy change for the given reaction, you can use the Hess's law and standard enthalpy of formation data.
Here's how you can approach the calculation:
1. Write down the balanced chemical equation for the reaction, including the state symbols for each species involved.
2. Split the equation into a sum of two reactions: one where all the reactants and products are in their standard states, and the other reaction where the substances of interest are in their standard states.
3. Identify the standard enthalpy of formation values for each species involved in the reaction. These values represent the enthalpy change when one mole of the substance is formed from its constituent elements in their standard states.
4. Calculate the ΔH° for the reaction using the standard enthalpy of formation values and stoichiometric coefficients of the balanced equation. The ΔH° is given by the sum of the products' enthalpy of formation minus the sum of the reactants' enthalpy of formation.
In this case, notice that the Ba2+ and NO3- ions are spectator ions and do not participate in the overall reaction. Therefore, they can be ignored for the calculation of the standard enthalpy change.
In the given reaction, the substances of interest are NH4NO3 (aqueous) and NH3 (gaseous). So, we need to know the standard enthalpies of formation for NH4NO3 and NH3.
Next, follow these steps:
1. Write down the balanced chemical equation for the reaction:
Ba(OH)2(aq) + 2NH4NO3(aq) → 2NH3(g) + 2H2O(l)
2. Split the equation into two reactions:
Reaction 1: Ba(OH)2(aq) → Ba(OH)2(s)
Reaction 2: Ba(OH)2(s) + 2NH4NO3(aq) → 2NH3(g) + 2H2O(l)
3. Look up the standard enthalpies of formation for Ba(OH)2(s), NH4NO3(aq), NH3(g), and H2O(l). You can find these values in standard enthalpy of formation tables.
4. Calculate the ΔH° of Reaction 2 using the standard enthalpies of formation:
ΔH° = [2 × ΔH°f(NH3)] + [2 × ΔH°f(H2O)] - [ΔH°f(Ba(OH)2(s))] - [2 × ΔH°f(NH4NO3(aq))]
Once you have the values, plug them into the equation and calculate the standard enthalpy change. Make sure to use the correct sign conventions for exothermic or endothermic reactions.
Remember to check the units of the enthalpies of formation values and ensure consistency (e.g., kJ/mol).
I hope this helps! Let me know if you have any further questions.