Final answer:
To find the enthalpy change for the combustion of one mole of octane, first calculate the total heat released in the calorimeter, and then divide that by the moles of octane burned, taking the molar mass of octane into account.
Step-by-step explanation:
When a 1.800 g sample of octane (C8H18) is burned in a calorimeter with a heat capacity of 12.66 kJ/°C, and the temperature increase observed is from 22.36 °C to 28.78 °C, we can calculate the heat released (q) during combustion using the formula q = mcΔT, where m is the mass of the substance, c is the specific heat capacity of the calorimeter, and ΔT is the change in temperature.
To find the enthalpy change (ΔH) for the combustion of one mole of octane, the heat released is divided by the number of moles of octane that were burned. Since octane has a molar mass of 114.23 g/mol, the number of moles of octane in a 1.800 g sample is 1.800 g / 114.23 g/mol. After calculating the total heat released, this number is then used to find ΔH per mole.
The temperature change (ΔT) is 28.78 °C - 22.36 °C = 6.42 °C. The heat released (q) can be calculated as q = (12.66 kJ/°C) * (6.42 °C). Finally, to find ΔH combustion per mole, divide the total heat released by the moles of octane burned.