A sample of benzene, C 6 H 6 , weighing 3.65 g was burned in an excess of oxygen

Question

A sample of benzene, C6H6, weighing 3.65 g was burned in an excess of oxygen in a bomb calorimeter.  The temperature of the calorimeter rose from 25.00ºC to 36.4 ºC....

A sample of benzene, C6He, weighing 3.65 g was burned in an excess of oxygen in a bomb calorimeter. The temperature of the calorimeter rose from 25.00°C to 36.4 °C. If the heat capacity of the calorimeter and contents was 12.05 kJro, what is the value in kJ of q for burning 0.114 mol of benzene at constant volume and 25.00°C? The reaction is: C6H60 O CO 2 (g) H2O 2 (g) Units

Explanation / Answer

Qcal = 12.05kJ/0C X (36.4 -25)0C

         = 12.05kJ/0C x 11.40C

                   = 137.37 kJ

The balanced chemical equation is:

C6H6(l) + 6 O2(g)--------------> 6 CO2(g) + 3 H2O(l).

The energy calculated is for 3.65g of benzene that is 3.65g/78g/mol

= 0.047moles

Hrxn or enthalpy of reaction is H for 0.114mole reaction. Since this is a combustion reaction Hrxn=Hcombustion,whereHcombustion is the enthalpy of combustion.

Hrxn for this equation is:

137.37kJ x 0.114mole / 0.047 moles = 333.2kJ

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