Heat of Combustion Lab

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Heat of Combustion Lab
Directions: In this activity, you will use experimental data obtained
from a bomb calorimeter to calculate the molar heat of methane, CH 4
a hydrocarbon. You will then compare the experimental results with
the actual molar heat of combustion of methane and calculate the
percent error.
1. You may recall that the products of the complete combustion of a
hydrocarbon are water vapor and carbon dioxide gas. Write the balanced
equation showing the combustion of methane. Do not forget to include the
states of matter of the reactants and the products. Hint: Methane is a gas at
standard temperature and pressure.
CH2+2O2-> 2H20+CO2
To begin the experiment, 1.11g of methane CH 4 is burned in a bomb
calorimeter containing 1000 grams of water. The initial temperature of water
is 24.85oC. The specific heat of water is 4.184 J/g oC. The heat capacity of
the calorimeter is 695 J/ oC . After the reaction the final temperature of the
water is 35.65oC.
2. Calculate the change in temperature, ΔT
10.80C
3. Using the formula q water = m • c • ΔT ,calculate the heat absorbed by the water
45187.2J
4. Using the formula q cal = Ccal • ΔT ,calculate the heat absorbed by the
calorimeter.
7506J
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5. The total heat absorbed by the water and the calorimeter can be calculated
by adding the heat calculated in steps 3 and 4. The amount of heat released
by the reaction is equal to the amount of heat absorbed with the negative
sign as this is an exothermic reaction. Using the formula ∆H = - (q cal + q water ) ,
calculate the total heat of combustion.
-52693.2
6. Evaluate the information contained in this calculation and complete the
following sentence:
1.11
This calculation shows that burning ____________
grams of methane [takes
in/gives off] ______________ energy.
7. The molar mass of methane is 16.04 g/mol. Calculate the number of moles
of methane burned in the experiment.
8. What is the experimental molar heat of combustion?
9. The accepted value for the heat of combustion of methane is -890 KJ/mol .
Explain why the experimental data might differ from the theoretical value.
10.Give the formula % error =
theoretical value - experimental value
×100 , calculate
theoretical value
the percent error for the experiment.
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