Question

the thermodynamics of ethanol
molar enthalpy of combustion
through calorimetry, the researcher determines that a 1.000 - gram sample of pure ethanol releases 28.76 kilojoules of heat.
\\(\ce{c2h5oh(l) + 3o2(g) -> 2co2(g) + 3h2o(g)}\\)
what is the molar heat of combustion for ethanol in kilojoules per mole at 25 °c?
-57.52 kj/mol
-28.76 kj/mol
-1325 kj/mol
-2650. kj/mol

Explanation:

Step1: Calculate molar mass of ethanol

Ethanol formula: \( C_2H_5OH \) (or \( C_2H_6O \)). Molar mass: \( 2\times12.01 + 6\times1.008 + 16.00 = 46.07 \, \text{g/mol} \).

Step2: Find moles of ethanol

Moles \( n = \frac{\text{mass}}{\text{molar mass}} = \frac{1.000 \, \text{g}}{46.07 \, \text{g/mol}} \approx 0.02171 \, \text{mol} \).

Step3: Calculate molar heat of combustion

Heat released for 1.000 g: \( 28.76 \, \text{kJ} \) (but combustion is exothermic, so sign is negative). Molar heat: \( \frac{-28.76 \, \text{kJ}}{0.02171 \, \text{mol}} \approx -1325 \, \text{kJ/mol} \).

Answer:

-1325 kJ/mol