6.3 g of pentaborane, B5H11 is burnt in the presence of O2 to yield H2O(l) and boron oxides. The reaction was performed in an open container and 157.2 kJ of heat was produced at standard conditions.

What is the ΔcombH of pentaborane in kJ/mol to 2 d.p?

Question

6.3 g of pentaborane, B5H11 is burnt in the presence of O2 to yield H2O(l) and boron oxides. The reaction was performed in an open container and 157.2 kJ of heat was produced at standard conditions.

What is the ΔcombH of pentaborane in kJ/mol to 2 d.p?

BlackTom AI · Accepted Answer

To find the standard enthalpy change of combustion (Δ_combH) of pentaborane (B5H11), we need to calculate the heat released per mole of B5H11.

1. **Molar Mass Calculation:**
   - The molar mass of B5H11 is calculated as follows:
     - Boron (B): 5 atoms × 10.81 g/mol = 54.05 g/mol
     - Hydrogen (H): 11 atoms × 1.008 g/mol = 11.088 g/mol
     - Total molar mass of B5H11 = 54.05 g/mol + 11.088 g/mol = 65.138 g/mol

2. **Moles of B5H11 Burnt:**
   - Given mass of B5H11 = 6.3 g
   - Moles of B5H11 = 6.3 g / 65.138 g/mol = 0.0967 mol

3. **Heat Released Per Mole:**
   - Total heat released = 157.2 kJ
   - Heat released per mole of B5H11 = 157.2 kJ / 0.0967 mol = 1625.39 kJ/mol

4. **Result:**
   - The Δ_combH of pentaborane is -1625.39 kJ/mol (negative sign indicates exothermic reaction).

Thus, the Δ_combH of pentaborane is -1625.39 kJ/mol to two decimal places.

6.3 g of pentaborane, B5H11 is burnt in the presence of O2 to yield H2O(l) and boron oxides. The reaction was performed in an open container and 157.2 kJ of heat was produced at standard conditions. What is the ΔcombH of pentaborane in kJ/mol to 2 d.p?简答题

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