Question

Sulfur (2.56 g) is burned in a bomb calorimeter with excess O2(g). The temperature increases from 21.25 °C to 26.72 °C. The bomb has a heat capacity of 923 J/K, and the calorimeter contains 815 g of water.

Calculate the heat evolved, per mole of SO2 formed, in the course of the reaction:

S8(s) + 8 O2(g) --> 8 SO2(g)

Answer is in kJ.

A. 301.2

B. 3410

C. 296.3

D. 145.1

Answer 1

Q = Ccal*delta T + m(water)*C(water)*delta T

= 923*(26.72 - 21.25) + 815*4.184*(26.72-21.25)

= 5048.81 + 18652.48

= 23701.29 J

= 23.70 KJ

Now calculate the mol of SO2 formed

Molar mass of S8 = 256.56 g/mol

mass of S8 = 2.56 g

mol of S8 = (mass)/(molar mass)

= 2.56/2.566*10^2

= 9.978*10^-3 mol

According to balanced equation

mol of SO2 formed = (8/1)* moles of S8

= (8/1)*9.978*10^-3

= 7.983*10^-2 mol

Heat evolved per mol of SO2 = heat / mol of SO2

= 23.70 KJ / (7.983*10^-2 mol)

= 296.9 KJ

Answer: C