A sample of 2.327 g of liquid toluene initially at 17.0 degree C and 0.5000 bar

Question

A sample of 2.327 g of liquid toluene initially at 17.0 degree C and 0.5000 bar is raised to 34.0C and 3.500 bar. Use the data from Table 2.4 [Appendix] at 298.15K and I bar and assume these values are constant over the range of pressure and temperature of interest. (a) Using the density from Table 2.4, calculate the molar volume of toluene and the volume of this sample. (b) Using the approximation of Equation 3.46, calculate the change of enthalpy of the toluene sample as a result of the change of temperature and as a result of the change in pressure, and the total change of enthalpy for the process.

Explanation / Answer

(a) Using density, calculate the molar volume of toluene and the volume
of this sample
Density, rho = 0.87g/ml
Molar mass, MW = 92.14g/mol
Molar volume, v = MW/rho= 105.9 ml/mol
Volume of 2.327g toluene, V = W/rho=2.327/0.87=2.67ml

(b) Using approximation dH = cp*dT+v*dP, calculate the change of enthalpy of toluene sample and the

total enthalpy change for the process.

Heat capacity, cp = 156J/(mol K)
Average molar volume, v = 105.9 ml/mol=105.9E-6 m3/mol
change in temperature, dT=34-17=17K
change in pressure, dP=3.5-0.5=3bar=3E5N/m2
enthalpy change of sample, dH = cp*dT+v*dP = 156*17+105.9E-6*3E5= 2684J/mol =2.68kJ/mol

Total enthalpy change is also 2.68kJ/mol as there is no enthalpy change due to reaction

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