Bomb Calorimetry and Combustion Reactions

Introduction

• Bomb Calorimeter: A sealed vessel used in calorimetry problems.
  • Key identifier: Presence of the term "bomb calorimeter" and a capital "C" indicating the heat capacity.

Problem Overview

• Objective: Determine the heat produced by the combustion of a glucose sample.
• Components of the System:
  • Mass of glucose combusted.
  • Bomb calorimeter with a specified heat capacity.
  • Water contained inside the calorimeter.

Key Concepts

• Combustion Reaction:

  • Combustion in a calorimeter is exothermic, releasing heat.
  • Heat released raises the temperature of the calorimeter and its contents.

• Heat Capacity (C):

  • Heat capacity of bomb calorimeter provided: 893 J/°C.
  • Used to calculate heat change in the calorimeter.

Calculations

1. Temperature Change:

   • Initial Temperature: 23.8°C
   • Final Temperature: 35.6°C
   • 9T (Delta T): 35.6 - 23.8 = 11.8°C

2. Heat Calculations:

   • Heat absorbed by water (Q_water):

     • Mass of water: 775 g
     • Specific heat capacity of water (c): 4.184 J/g°C
     • Q_water = mass * specific heat * ΔT
     • Q_water = 775 g * 4.184 J/g°C * 11.8°C
     • Result: 38,300 J

   • Heat absorbed by calorimeter (Q_calorimeter):

     • Q_calorimeter = C * ΔT
     • C = 893 J/°C
     • Q_calorimeter = 893 J/°C * 11.8°C
     • Result: 10,500 J

3. Total Heat Calculation:

   • Total heat absorbed = Q_water + Q_calorimeter = 48,800 J
   • Heat released by reaction (Q_reaction) = - Total heat absorbed
   • Q_reaction = -48,800 J

Conclusion

• Exothermic Reaction: Negative Q value confirms an exothermic reaction.
• Unit Conversion:
  • Convert J to kJ if required: -48.8 kJ
  • Conversion factor: 1 kJ = 1,000 J

Additional Notes

• Always check the units in the final answer.
• Consider the requirements of the problem (Joules vs. kilojoules).