While researching energy values of fuels, a chemist designed an experiment to find out the heat of combustion of pentane. Using the known hexane heat of combustion of hexane = 4650kJ/mol and the data below calculate the heat of combustion of pentane.
Set up= copper beaker 42.5g filled with 500ml water and spirit burner underneath
DATA:
Initial temp= 26, final temp = 28.75 mass hexane = 10.11g
Initial temp= 26, final temp = 27.33 mass pentane = 8.15g
Specific heat capacity water= 4.18 and copper=0.39
To calculate the heat of combustion of pentane, we can use the equation:
Heat released = (mass of substance) * (specific heat capacity of substance) * (change in temperature)
First, let's calculate the heat released for hexane using the given data and the specific heat capacity of water.
For hexane:
Mass of hexane = 10.11g
Specific heat capacity of water = 4.18 J/g°C
Change in temperature = 28.75°C - 26°C = 2.75°C
Heat released for hexane = (10.11g) * (4.18 J/g°C) * (2.75°C) = 118.19 J
Next, let's calculate the heat released for pentane using the given data and the specific heat capacity of water.
For pentane:
Mass of pentane = 8.15g
Specific heat capacity of water = 4.18 J/g°C
Change in temperature = 27.33°C - 26°C = 1.33°C
Heat released for pentane = (8.15g) * (4.18 J/g°C) * (1.33°C) = 45.42 J
Since we are given the heat of combustion of hexane, which is 4650 kJ/mol, and we know the molar mass of hexane is 86.18 g/mol, we can calculate the heat released per mole of hexane:
Heat released per mole of hexane = (118.19 J) / (10.11g) * (86.18g/mol) = 1067.79 J/mol
Now, we can use the heat released per mole of hexane to calculate the heat released per mole of pentane by setting up a proportion:
Heat released per mole of pentane / Heat released per mole of hexane = (Mass of pentane) / (Mass of hexane)
Heat released per mole of pentane / 1067.79 J/mol = 8.15g / 10.11g
Heat released per mole of pentane = (8.15g / 10.11g) * 1067.79 J/mol
Heat released per mole of pentane = 860.31 J/mol
Therefore, the heat of combustion of pentane is approximately 860.31 J/mol.