Calculate the delta H for the reaction :
2H3BO3(aq) reacts with B2O3(solid) + 3H2O
To calculate the enthalpy change (ΔH) for the reaction, we need to know the standard enthalpies of formation (ΔHf) for the reactants and products involved in the reaction. However, if we do not have the ΔHf values available, we can use Hess's Law to calculate ΔH using other known reactions.
In this case, we can break down the given reaction into the following steps:
1. Formation of B2O3 from its elements:
3/2 O2(g) + B(s) → B2O3(s)
2. Formation of 2H3BO3 from its elements:
3/2 O2(g) + 3H2(g) + B(s) → 2H3BO3(aq)
3. Formation of 3H2O from its elements:
3/2 O2(g) + 3H2(g) → 3H2O(l)
By using the known ΔHf values for these individual reactions, we can calculate the ΔH for the overall reaction by applying the following steps:
Step 1: Multiply the first reaction by 2 to balance the B atoms:
2(3/2 O2(g) + B(s) → B2O3(s)) → 2B2O3(s)
Step 2: Multiply the second reaction by 2 to balance the B and H3BO3 coefficients:
2(3/2 O2(g) + 3H2(g) + B(s) → 2H3BO3(aq)) → 3H2BO3(aq)
Step 3: Add the reactions together:
2B2O3(s) + 3H2O(l) → 3H2BO3(aq)
Now, we need to consider the ΔH values for each step and apply the appropriate sign changes:
ΔH1 = ΔHf(B2O3) - ΔHf(B) - 3/2 ΔHf(O2)
ΔH2 = 2ΔHf(H3BO3) - 2ΔHf(B) - 3ΔHf(H2) - 3/2 ΔHf(O2)
ΔH3 = 3ΔHf(H2O) - 3/2 ΔHf(O2) - 3ΔHf(H2)
Finally, we can substitute the known ΔHf values and calculate ΔH:
ΔH1 = ΔHf(B2O3) - 0 - (3/2 ΔHf(O2))
ΔH2 = 2ΔHf(H3BO3) - 0 - (3ΔHf(H2) + 3/2 ΔHf(O2))
ΔH3 = 3ΔHf(H2O) - (3/2 ΔHf(O2)) - 3ΔHf(H2)
ΔH overall = ΔH1 + ΔH2 + ΔH3
Please note that ΔH values differ for different materials, and their values cannot be provided without specific information about the materials' enthalpies of formation.
To calculate the enthalpy change (ΔH) for a reaction, you need to use the enthalpy values of the reactants and products. In this case, you will need the enthalpy values for H3BO3 (boric acid), B2O3 (boron trioxide), and H2O (water).
1. Start by writing the balanced chemical equation for the reaction:
2H3BO3(aq) + B2O3(s) + 3H2O(l)
2. Find the ΔH values for the species involved in the reaction. ΔH is typically given in kJ/mol of the substance in question. In this case, you'll need the values for H3BO3, B2O3, and H2O.
3. Add up the ΔH values for the reactants, taking into account their stoichiometric coefficients. Multiply each ΔH value by the corresponding coefficient and sum them up:
ΔH = (2 * ΔH[H3BO3(aq)]) + (1 * ΔH[B2O3(s)]) + (3 * ΔH[H2O(l)])
4. Finally, substitute the values you obtained in step 3 and calculate the overall ΔH for the reaction. Make sure to include the units (kJ):
ΔH = (2 * ΔH[H3BO3(aq)]) + (1 * ΔH[B2O3(s)]) + (3 * ΔH[H2O(l)])
dHrxn = (n*dHf products) - (n*dHf reactants)
Look up delta H formation in tables (usually in the back of your text but also on the web), plug into the above and calculate.