The molar enthalpy of combustion of ethanol is -1234.8kJ/mol. How much water can be heated from 10.85 degrees celsius to 72.6 degrees celsius by the combustion of 42.2 g of ethanol.

Answer 1

To solve this problem, we need to use the equation:

q = mcΔT

Where:
q = heat energy absorbed by water (in joules)
m = mass of water (in grams)
c = specific heat capacity of water (4.18 J/g°C)
ΔT = change in temperature (final temperature - initial temperature) (in °C)

First, let's calculate the moles of ethanol burned:

1 mole of ethanol = 46.07 g
42.2 g of ethanol = 42.2 g / 46.07 g/mol = 0.9162 mol of ethanol

Next, we will calculate the heat energy released by the combustion of 1 mole of ethanol:

Molar enthalpy of combustion of ethanol = -1234.8 kJ/mol

Since 1 kJ = 1000 J, the molar enthalpy in joules is:
-1234.8 kJ/mol = -1234.8 x 1000 J/mol = -1,234,800 J/mol

Now, let's calculate the heat energy released by the combustion of 0.9162 mol of ethanol:

Heat energy released by combustion = -1,234,800 J/mol x 0.9162 mol = -1,131,259.76 J

Next, let's calculate the mass of water:

Mass of water = density of water x volume of water
As the volume of water is not given, we will assume it to be 1 liter (1000 grams) for this calculation.

Mass of water = 1000 grams

Finally, let's calculate the change in temperature:

ΔT = final temperature - initial temperature = 72.6°C - 10.85°C = 61.75°C

Now, let's calculate the heat energy absorbed by the water:

q = mcΔT
q = 1000 g x 4.18 J/g°C x 61.75°C = 258,695 J

Since the negative sign in the molar enthalpy of combustion indicates that heat is being released, we need to reverse the sign of the heat energy released by the combustion:

Heat energy released by combustion = -(-1,131,259.76 J) = 1,131,259.76 J

Finally, let's calculate the amount of water that can be heated:

Mass of water heated = q / heat energy released by combustion
Mass of water heated = 258,695 J / 1,131,259.76 J = 0.2286

Therefore, approximately 0.23 kg (or 230 grams) of water can be heated from 10.85°C to 72.6°C by the combustion of 42.2g of ethanol.