Methanol(MM=32.04g/mole) is sometimes used as fuel for race cars, since methanol fires are easily extinguished with water. the energy content o methanol is investigated in a high-quality calorimeter for which the heat capacity is known to be 4.5Kj/C. When 17.62g of liquid of methanol is burned in the calorimeter. its temperature rises from 21 to 99.03celicus. Find the enthalpy for the combustion of methanol.

Question

Methanol(MM=32.04g/mole) is sometimes used as fuel for race cars, since methanol fires are easily extinguished with water. the energy content o methanol is investigated in a high-quality calorimeter for which the heat capacity is known to be 4.5Kj/C. When 17.62g of liquid of methanol is burned in the calorimeter. its temperature rises from 21 to 99.03celicus. Find the enthalpy for the combustion of methanol.

I used the equation q = ms(Tfinal - Tinitial) and i got an answer of 5394.09kJ. Did i do it correctly?

Answer 1

If you used that equation, you are not going to get the right answer.

Heat of combustion is often tabulated in kJ/mole OR kJ/gram

Lets do it in moles.

Heatcombustion*molesMethanol=heatcapacity*(Tf-Ti)

heatcombustion*17.62/32.04=4.5kJ/C*(78.03C)

solve for heat combustion in J/mole

Answer 2

okay i knew i was doing something wrong when i used that formula. Thanks! I got an answer of 639.59 kJ/mol, it seems about right.

Answer 3

To determine the enthalpy for the combustion of methanol, you can use the equation:

q = mcΔT

where q is the heat released or absorbed, m is the mass of the substance being burned (methanol in this case), c is the heat capacity of the calorimeter, and ΔT is the change in temperature.

Given:
Mass of methanol (m) = 17.62 g
Heat capacity of the calorimeter (c) = 4.5 kJ/°C
Change in temperature (ΔT) = (99.03 °C - 21 °C) = 78.03 °C

Now, plug in these values into the equation:

q = (17.62 g) * (4.5 kJ/°C) * (78.03 °C)

Notice that the units for mass and heat capacity need to be consistent, so convert grams to moles since the molar mass is given.

To convert grams to moles, use the formula:

moles = mass (g) / molar mass (g/mol)

Given:
Molar mass of methanol (MM) = 32.04 g/mol

moles = 17.62 g / 32.04 g/mol

Calculate moles:
moles = 0.549 moles (rounded to three decimal places)

Now, multiply the moles by the change in enthalpy per mole to find the total heat released (enthalpy) for the combustion of methanol:

q = (0.549 moles) * (−782.86 kJ/mol)

Notice that the enthalpy of combustion of methanol is -782.86 kJ/mol, meaning it releases energy.

Calculate q:
q = -429.51 kJ (rounded to two decimal places)

So, the enthalpy for the combustion of methanol is approximately -429.51 kJ.