Question

0.9410 g of phenol (C6H5OH) are burned in a bomb calorimeter with a heat capacity of 4.630 kJ/C . The temperature of the calorimeter increases by 6.590C. What is the heat of combustion (Hrxn for the process of burning) of phenol?

a. -30.51 kJ/C
b. -267.5 kJ/C
c. -3051 kJ/mol
d. none of these

Answer 1

Q cal = Ccal*delta T

Q cal = 4.63*(6.59-0.0)

Q cal = 30.51 KJ

This heat is supplied by C6H5OH

Molar mass of C6H5OH = 6*MM(C) + 6*MM(H) + 1*MM(O)

= 6*12.01 + 6*1.008 + 1*16.0

= 94.108 g/mol

mass of C6H5OH = 0.9410 g

we have below equation to be used:

number of mol of C6H5OH,

n = mass of C6H5OH/molar mass of C6H5OH

=(0.941 g)/(94.108 g/mol)

= 9.999*10^-3 mol

delta H = -Qcal/number of mol

delta H = -30.51/9.999*10^-3

delta H = -3.051*10^3 KJ/mol

delta H = -3051 KJ/mol

Answer: c