The combustion of benzoic acid releases 26.38kJ/g and is often used to calibrate a bomb calorimeter. the combustion of 1.045 g of benzoic acid caused the temperature of the calorimeter to rise by 5.985C. Useing the same calorimeter, a sample of 0.876g of octane (C8H18) was burned. The temperature increased by 8.518C. What is the molar enthalpy of the combustion of octane?
q = Ccal x delta T
26,380 J x 1.045g = Ccal x 5.985. Solve for Ccal.
q octane = Ccal x delta T. Solve for q which will be q/0.876g. You want q/mol. Take q/g x molar mass octane.
is delta T supposed to stay in Celsius or should i convert it to kelvin ?
It doesn't matter which you use. Since it is the difference you can see why.
20 C is 293 K
10 C is 283 K.
delta T in C is 20-10 = 10
delta T in K is 293-283 = 10
I always use C; converting to K is another step where I can make an error.
thank you so much!
To determine the molar enthalpy of combustion for octane (C8H18), we can use the calorimetry data and the molar mass of octane.
First, let's calculate the heat released by the combustion of benzoic acid using the given data. The heat released is given as 26.38 kJ/g.
Heat released by the combustion of benzoic acid = 26.38 kJ/g * 1.045 g = 27.54 kJ
Next, we can calculate the heat absorbed by the bomb calorimeter for the combustion of benzoic acid. The formula for heat is:
Heat = mass × specific heat × temperature change
Here, the mass of the calorimeter and water is not given, but since we are using the same calorimeter for both experiments, we can assume it is the same. Therefore, we can write:
Heat absorbed by the calorimeter and water (benzoic acid) = Heat released by the benzoic acid
Now, let's calculate the heat absorbed by the calorimeter and water for the combustion of octane. The temperature change is given as 8.518°C.
Heat absorbed by the calorimeter and water (octane) = mass × specific heat × temperature change
To determine the molar enthalpy of combustion for octane, we need to calculate the heat released per mole of octane burned.
Molar mass of octane (C8H18) = (12.01 g/mol × 8) + (1.01 g/mol × 18) = 114.23 g/mol
Now, we can calculate the molar enthalpy of combustion for octane using the following formula:
Molar enthalpy of combustion of octane = Heat absorbed by the calorimeter and water (octane) / moles of octane burned
To find the moles of octane burned, we can use the following equation:
moles = mass / molar mass
Substituting the values into the formula:
Molar enthalpy of combustion of octane = (Heat absorbed by the calorimeter and water (octane) / (mass of octane / molar mass of octane)
Finally, we can substitute the values into the equation and calculate the molar enthalpy of combustion for octane.