Question one: Part A When a 3.40 g sample of liquid octane (C8H18) is burned in

Question

Question one:

Part A When a 3.40 g sample of liquid octane (C8H18) is burned in a bomb calorimeter, the temperature of the calorimeter rises by 27.5 C. The heat capacity of the calorimeter, measured in a separate experiment, is 6.12 kJ/C . Determine Erxn for the combustion of octane in units of kJ/mol octane. Express your answer using three significant figures.

Question two:

Part A

Under what conditions is the change in internal energy, E rxn , equal to the heat evolved in a reaction?

Under what conditions is the change in internal energy, E rxn , equal to the heat evolved in a reaction?

E rxn is never equal to the heat evolved in a reaction.

can someone explain how to do these?

E rxn is never equal to the heat evolved in a reaction.

can someone explain how to do these?

Explanation / Answer

1 )

Q = Cp dT

Q = ( 6.12 kJ /oC ) x (27.5 oC)

Q = 168.3 kJ

moles of octane = 3.40 / 114 = 0.0298

0.0298 moles ----------------------> 168.3 kJ energy

1 mole --------------------------> 168.3 / 0.0298 = 5643 kJ / mole

E rxn = -5643 kJ / mol

negative means in combustion heat liberated .

2)

Constant volume

reason : the heat content of a system at constant volume is known as change in internal energy.

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