Thermo12 Bomb Cal.notebook
September 27, 2016
Sep 27­10:27 AM
Calculating ∆Hrxn: Method 4 Bomb Calorimetry
Ø Measures enthalpy changes during combustion reactions
Ø Bomb calorimeter consists of many components, so heat absorbed by the instrument must be accounted for
Ø Manufacturers provide a value called the heat capacity of the calorimeter (C): the total energy absorbed or released per °C for the calorimeter and its contents (units: J or kJ/°C)
Feb 17­1:50 PM
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Thermo12 Bomb Cal.notebook
September 27, 2016
Ex1: 1.50 g of sucrose (MM = 342.34 g/mol) is put in a bomb calorimeter (C = 8.57 kJ/°C). The temperature changes from 25.00°C to 27.88°C. Calculate the molar enthalpy of combustion.
Feb 17­1:52 PM
Ex2: Calculate the molar enthalpy of combustion of stearic acid, C18H36O2, if 1.14 g of the substance was combusted in the same bomb calorimeter as Ex1 and the temperature changed from 25.00°C to 30.38°C.
Feb 17­1:52 PM
2
Thermo12 Bomb Cal.notebook
September 27, 2016
Practice Problems
1. a) An oxygen bomb calorimeter has a heat capacity of 6.49 kJ/°C. The complete combustion of 1.12 g of acetylene produces a maximum temperature increase of 8.55 °C. Calculate the molar enthalpy of combustion for acetylene, C2H2 (g).
b) Canadian inventors have developed zeolite, a natural aluminum silicate mineral, as a storage medium for solar heat. Zeolite releases heat when hydrated with water. In a test, zeolite is used to heat water in a tank that has a heat capacity of 157 kJ/°C. What is the enthalpy change of hydration (∆H) for zeolite if the temperature of the water increases from 27°C to 73°C?
2. A lab technician places a 5.00 g food sample into a bomb calorimeter that is calibrated at 9.23 kJ/°C. The initial temperature of the calorimeter system is 21.0°C. After burning the food, the final temperature of the system is 32.0°C. What is the heat of combustion of the food in kJ/g?
3. The energy content of food is determined by combustion in a bomb calorimeter that has a heat capacity of 9.22 kJ/°C. When 3.00 g of butter is burned in excess oxygen, the temperature of the bomb calorimeter changes from 19.62°C to 31.89°C. Calculate the specific enthalpy of combustion of butter in units of kJ/g.
4. A chemist wants to calibrate a new bomb calorimeter. He completely burns a mass of 0.930 g of carbon in a calorimeter. The temperature of the bomb calorimeter changes from 25.00°C to 28.15°C. If the molar enthalpy of combustion of carbon is 394 kJ/mol, what is the heat capacity of the new calorimeter? What evidence shows that the reaction was exothermic?
Feb 17­1:52 PM
Feb 22­12:50 PM
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Thermo12 Bomb Cal.notebook
September 27, 2016
Hess' Law: Prelab
To prepare for tomorrow's lab, write and balance the
following reactions:
1) Solid magnesium oxide reacts with hydrochloric acid.
2) Solid magnesium reacts with hydrochloric acid.
3) Heat of formation of liquid water.
Target reaction: Heat of formation of magnesium
oxide. (include ΔH for this reaction)
Sep 27­11:06 AM
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