A 1.000 g sample of ethanol, C2H5OH was burned in a coffee cup calorimeter containing 1220 mL of water. The temperature of the water in the calorimeter increased by 5.25C . What is the molar enthalpy of combustion in kJ/mol?

Answer 1

To calculate the molar enthalpy of combustion, we need to first find the amount of heat transferred to the water in the calorimeter.

The heat transferred can be determined using the equation:

q = mcΔT

Where:
q = heat transferred
m = mass of water
c = specific heat capacity of water
ΔT = change in temperature

The specific heat capacity of water is 4.18 J/g°C. Converting the mass of water from mL to g:

mass of water = 1220 mL = 1220 g

Now, we can calculate the heat transferred:

q = (1220 g)(4.18 J/g°C)(5.25°C)
q = 27,343 J

Next, we need to convert the units of heat to kJ:

q = 27,343 J ÷ 1000 = 27.343 kJ

Since the ethanol sample weighed 1.000 g, the molar enthalpy of combustion can be calculated using the equation:

Molar enthalpy of combustion = q ÷ n

Where:
q = heat transferred (27.343 kJ)
n = moles of ethanol

The molar mass of ethanol (C2H5OH) is:
C = 12.01 g/mol
H = 1.01 g/mol (x 5 atoms)
O = 16.00 g/mol

Molar mass of ethanol = 12.01 + (1.01 x 5) + 16.00 = 46.07 g/mol

Now, we can calculate the moles of ethanol:

moles of ethanol = 1.000 g ÷ 46.07 g/mol
moles of ethanol ≈ 0.0217 mol

Finally, we can calculate the molar enthalpy of combustion:

Molar enthalpy of combustion = 27.343 kJ ÷ 0.0217 mol
Molar enthalpy of combustion ≈ 1259.4 kJ/mol

Therefore, the molar enthalpy of combustion of ethanol is approximately 1259.4 kJ/mol.