Constant-Volume Calorimetry Video Lessons

Concept: Heat of Combustion

# Problem: The same reaction, with exactly the same amount of reactant, is conducted in a bomb calorimeter and in a coffee-cup calorimeter. In one of the calorimeters, qrxn = -12.5 kJ and in the other qrxn = -11.8 kJ. Which value was obtained in the bomb calorimeter? (Assume that the reaction has a positive ΔV in the coffee-cup calorimeter.)

###### FREE Expert Solution

Bomb calorimeter → constant volume:

${\mathbf{q}}_{\mathbf{sol}\mathbf{\text{'}}\mathbf{n}}\mathbf{=}\mathbf{q}$

Coffee cup calorimeter → constant pressure, but volume changes

${\mathbf{q}}_{\mathbf{sol}\mathbf{\text{'}}\mathbf{n}}\mathbf{=}\mathbf{q}\mathbf{-}\mathbf{P}\mathbf{∆}\mathbf{V}$

• work done by reaction = -PΔV

Therefore, qsoln from coffe cup calorimeter is lower than for bomb calorimeter

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###### Problem Details

The same reaction, with exactly the same amount of reactant, is conducted in a bomb calorimeter and in a coffee-cup calorimeter. In one of the calorimeters, qrxn = -12.5 kJ and in the other qrxn = -11.8 kJ. Which value was obtained in the bomb calorimeter? (Assume that the reaction has a positive ΔV in the coffee-cup calorimeter.)