Question

the combustion of 3.00 grams of octane, c₈h₁₈, in a bomb calorimeter resulted in a temperature increase of 51.2 °c. c₈h₁₈ + \\(\frac{5}{2}\\)o₂ → 8co₂ + 9h₂o δh₍comb₎ = −5461 kj/mol what is the heat of reaction when 3.00 g c₈h₁₈ burns? q₍comb₎ = ? kj enter either a + or - sign and the magnitude. do not round until the end. use significant figures.

Explanation:

Step1: Calculate molar mass of \( C_8H_{18} \)

Molar mass of \( C \) is \( 12.01 \, g/mol \), \( H \) is \( 1.008 \, g/mol \).
Molar mass \( = 8\times12.01 + 18\times1.008 = 96.08 + 18.144 = 114.224 \, g/mol \).

Step2: Find moles of \( C_8H_{18} \)

Moles \( = \frac{mass}{molar \, mass} = \frac{3.00 \, g}{114.224 \, g/mol} \approx 0.02626 \, mol \).

Step3: Calculate heat of reaction

\( \Delta H_{comb} = -5461 \, kJ/mol \), so heat released (\( q_{comb} \)) is moles \( \times \Delta H_{comb} \).
\( q_{comb} = 0.02626 \, mol \times (-5461 \, kJ/mol) \approx -143.4 \, kJ \) (rounded to significant figures, 3 sig figs from 3.00 g).

Answer:

\(-143\) (or more precisely \(-143.4\) depending on sig fig interpretation, but 3.00 has 3 sig figs, so \(-143\) or \(-143.4\) if considering more decimals)