Answer:
The combustion of diborane (B2H6) is as follows:
2B2H6(g) + 6O2(g) → 4H2O(g) + B4O(g)
The balanced chemical equation shows that 2 moles of B2H6 react with 6 moles of O2 to produce 4 moles of H2O and 1 mole of B4O. We can use this information to calculate the amount of heat released by the combustion of 0.491 g of B2H6:
0.491 g B2H6 × (1 mol B2H6/27.67 g B2H6) × (1 mole B4O/2 moles B2H6) × (-2037 kJ/mol B4O) = -7.89 kJ
The negative sign indicates that the reaction releases heat.
The heat released by the reaction is absorbed by the calorimeter, which causes its temperature to increase. We can use the equation:
q = Ccalorimeter × ΔT
where q is the amount of heat absorbed by the calorimeter, Ccalorimeter is the heat capacity of the calorimeter, and ΔT is the change in temperature of the calorimeter.
Rearranging the equation, we get:
ΔT = q/Ccalorimeter
Substituting the values we obtained, we get:
ΔT = (-7.89 kJ)/(7.854 kJ/°C) = -1.005°C
The negative sign indicates that the temperature of the calorimeter decreases by 1.005°C. Therefore, the final temperature of the calorimeter is:
19.63°C - 1.005°C = 18.625°C
Rounding to the appropriate number of significant figures, the final temperature of the calorimeter is 18.6°C.
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