The air (defined as the system) in a cylinder-piston assembly absorbs 125 J of h

Question

The air (defined as the system) in a cylinder-piston assembly absorbs 125 J of heat from an external flame. The volume of air expands against a constant external pressure of 2.60 atm from 0.150 L to 0.450 L Calculate the change in internal energy for the air in the cylinder-piston assembly. 46.0 J 204 J 124 J -204 68.3 J When 0.514 g of biphenyl (C_12H_10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.8 degree C to 29.4 degree C. Find delta E_rxn for the combustion of biphenyl in kJ/mol C_12H_10. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/degree C. -21.1 kJ/mol C_12H_10 -6.33 times 10^3 kJ/mol C_12H_10 -1.67 times 10^3 kJ/mol C_l2H_10 -41.0 kJ/mol C_12H_10 -3.25 times 10^3 kJ/mol C_12H_10

Explanation / Answer

When 0.514 g of biphenyl (C12H10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.8 C to 29.4 C. Find E rxn for the combustion of biphenyl in kJ/mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/ C.

OPTION B

answer = - 6.30 * 10^3 kJ/mol

heat of combustion = heat capacity of calorimter x T
Q = 5.86kJ/ºC x 3.6ºC = 21.096kJ

0.514g / 154g/mole = 0.00334moles

21.096kJ / 0.00334moles = 6.32x10^3kJ/mole

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question 38

option C

deltaE = q + w

= -125 J-P delta v

=-125 J -2.60 (0.3)

=124j -answer

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