Specific Heat Capacity and Energy Calculations

Introduction

• Objective: Calculate energy stored or released from a system when temperature changes.
• Example: Boiling water to understand energy stored in hot water.

Specific Heat Capacity

• Definition: Amount of energy required to raise the temperature of 1 kg of a substance by 1°C.
• Units: Joules per kilogram per degree Celsius (J/kg°C).

Sample Calculation

• Question: Calculate energy needed to heat 2 kg of water from 20°C to 100°C.
• Specific Heat Capacity of Water: 4200 J/kg°C.
• Equation:
  • Change in Thermal Energy (J) = Mass (kg) x Specific Heat Capacity (J/kg°C) x Temperature Change (°C).
• Values:
  • Mass = 2 kg
  • Temperature Change = 100°C - 20°C = 80°C
• Calculation:
  • Energy = 2 kg x 4200 J/kg°C x 80°C = 67,200 J
  • Convert to kilojoules: 67,200 J / 1000 = 67.2 kJ

Practice Question 1

• Scenario: Aluminum plate with mass 1.5 kg heated from 20°C to 200°C.
• Specific Heat Capacity of Aluminum: 913 J/kg°C.
• Values:
  • Mass = 1.5 kg
  • Temperature Change = 200°C - 20°C = 180°C
• Calculation:
  • Energy = 1.5 kg x 913 J/kg°C x 180°C = 246,510 J
  • Convert to kilojoules: 246,510 J / 1000 = 246.51 kJ

Practice Question 2

• Scenario: Hot water bottle cools from 80°C to 20°C releasing 76,000 J.
• Specific Heat Capacity of Water: 4200 J/kg°C.
• Rearranged Equation: Mass = Thermal Energy Change / (Specific Heat Capacity x Temperature Change)
• Values:
  • Thermal Energy Change = 76,000 J
  • Temperature Change = 80°C - 20°C = 60°C
• Calculation:
  • Mass = 76,000 J / (4200 J/kg°C x 60°C) = 3 kg

Conclusion

• You should now be able to calculate energy changes using specific heat capacity.
• Additional Resource: Vision workbook available for more practice questions.