6.3.2 Bomb Calorimetry (Constant Volume) Flashcards Preview

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Flashcards in 6.3.2 Bomb Calorimetry (Constant Volume) Deck (11)
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1
Q

Bomb Calorimetry (Constant Volume)

A
  • A bomb calorimeter (constant volume calorimeter) is a steel container within a second steel container; the calorimeter is sealed and held at constant volume.
  • Constant volume calorimetry is useful for finding the change in internal energy (ΔE) for chemical reactions.
2
Q

note

A
  • A bomb calorimeter (constant volume calorimeter) is
    constructed from a steel “bomb” within a second steel
    container. This construction allows for the measurement of heat at constant volume.
  • The heat capacity of the calorimeter and its contents must be considered when performing bomb calorimetry
    calculations. The heat capacity of the calorimeter and its contents is the sum of the heat capacity of the calorimeter (C calorimeter ) and the molar heat capacity at constant volume for water (c v ) multiplied by the moles of water present in the calorimeter.
  • Constant volume calorimetry is useful for finding the change in internal energy (ΔE) for chemical reactions.
  • Problem: 2.84 g ethanol (CH 3 CH 2 OH) is burned in excess oxygen in a bomb calorimeter. The temperature of the calorimeter changes from 25.00 ̊C to 33.73 ̊C. If the heat capacity of the calorimeter and its contents (C) is 9.63 kJ/ ̊C, what is the value of q for burning 1.00 mol ethanol at constant volume and 25.00 ̊C?
  • Calorimetry relies on the equality q sys = –q surr . In other words, the heat given off by the system is absorbed by the surroundings (the calorimeter). The heat of the surroundings is equal to the heat capacity of the calorimeter and its contents (C) multiplied by the change in temperature (ΔT, or T f – T i ). Using these values, the heat of the system is found to be –84.1 kJ—the reaction is exothermic.
  • Dividing this value by the moles of ethanol present (6.17 x 10 –2 mol) yields the heat for the combustion of 1 mol ethanol at constant volume and 25.00 ̊C (–1.36 x 10 3 kJ/mol).
  • The heat at constant volume (q v ) is equal to the change in internal energy (ΔE) for the reaction. Therefore, ΔE = –1.36 x 10 3 kJ/mol for the combustion of ethanol at 25.00 ̊C.
3
Q

Which of the following statements is true?

A

Bomb calorimeters are difficult to use and are not used in most labs.

4
Q

What does the C in the equation qsurr = CΔT represent?

A

The heat capacity of the calorimeter and its surroundings

5
Q

A reaction is carried out in a bomb calorimeter. Which of the following is TRUE if the heat of the reaction is found to be a negative value?

A

The heat of the surroundings increased

6
Q

A calorimeter has a heat capacity of 1.77 kJ / °C, and it contains 300 g of water. What is the heat capacity of the calorimeter and its surroundings given that the molar heat capacity of water is 75.374 J / mol°C?

A

3.03 kJ / °C

7
Q

What is a bomb calorimeter?

A

A device made of steel and used to measure the heat of a reaction

8
Q

Which of the following is not needed to find the heat of a reaction using a bomb calorimeter?

A

The change in air pressure

9
Q

Which device can be used to measure heat at constant volume?

A

Bomb calorimeter

10
Q

A bomb calorimeter has a stirrer. What is the stirrer used for?

A

To distribute the heat to bring all the water to a constant temperature

11
Q

A bomb calorimeter was used to measure the heat of combustion of naphthalene (C10H8 ). The temperature of the water rose from 25.00°C to 30.70°C. If 1.44 g of naphthalene was used, what is the heat of combustion of one mole of naphthalene? The heat capacity of the calorimeter and its surroundings is 10.17 kJ/°C.

A

−5160 kJ

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