A sample of ethanol 0.78g was burnes at a final temperature of 20.9°c. The mass of water is 50.0g. Calculate the standard enthalpy change of combustion of ethanol.
To calculate the standard enthalpy change of combustion of ethanol, we need to use the equation:
ΔH = q / n
where ΔH is the enthalpy change, q is the heat transferred in the reaction, and n is the number of moles of the substance being burned.
First, let's determine the heat transferred during the reaction (q). We can do this by using the equation:
q = mcΔT
where q is the heat transferred, m is the mass of the substance being heated (water in this case), c is the specific heat capacity of the substance (4.18 J/g·°C for water), and ΔT is the change in temperature.
Given that the mass of water is 50.0 g, and the final temperature change is 20.9°C, we can calculate the heat transferred during the reaction as follows:
q = (50.0 g) × (4.18 J/g·°C) × (20.9°C)
q = 4397.3 J
Next, we need to determine the number of moles of ethanol burned. To do this, we'll use the molar mass of ethanol, which is 46.07 g/mol. We can calculate the number of moles (n) using the equation:
n = mass / molar mass
Given that the mass of ethanol is 0.78 g, we can calculate the number of moles as follows:
n = 0.78 g / 46.07 g/mol
n ≈ 0.0169 mol
Finally, we can calculate the standard enthalpy change of combustion (ΔH) using the equation ΔH = q / n:
ΔH = (4397.3 J) / (0.0169 mol)
ΔH ≈ 260,239 J/mol
Therefore, the standard enthalpy change of combustion of ethanol is approximately 260,239 J/mol.