Question

3. A 2.200 g sample of quinone (CH,02) is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/°C. The temperature of the calorimeter increases from 23.44 to 30.57°C. a. What quantity of heat was produced by the combustion of the quinone? b. What is the heat of combustion per gram of quinone? c. What is the heat of combustion per mole of quinone?

Answer 1

a)

Q cal = Ccal*delta T

Q cal = 7.854*(30.57-23.44)

Q cal = 56.0 KJ

This heat is supplied by C6H4O2

Answer: 56.0 KJ

b)

mass(C6H4O2)= 2.200 g

delta H = -Qcal/number of mol

delta H = -56 KJ / 2.200 g

delta H = -25.5 KJ/g

Answer: -25.5 KJ/g

c)

Molar mass of C6H4O2,

MM = 6*MM(C) + 4*MM(H) + 2*MM(O)

= 6*12.01 + 4*1.008 + 2*16.0

= 108.092 g/mol

use:

number of mol of C6H4O2,

n = mass of C6H4O2/molar mass of C6H4O2

=(2.2 g)/(1.081*10^2 g/mol)

= 2.035*10^-2 mol

delta H = -Qcal/number of mol

delta H = -56/2.035*10^-2

delta H = -2.751*10^3 KJ/mol

Answer: -2.75*10^3 KJ/mol