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Temperature and Energy Units

Sep 7, 2025

Overview

This lecture covers temperature and energy units, explains specific heat, and demonstrates how calorimetry is used to calculate the caloric content of foods.

Temperature Units

  • The U.S. customary unit for temperature is degrees Fahrenheit (°F).
  • The metric unit for temperature is degrees Celsius (°C), also called centigrade.
  • The SI (International System) unit for temperature is Kelvin (K).
  • Freezing and boiling points of water: 32°F/212°F (Fahrenheit), 0°C/100°C (Celsius).
  • One degree Celsius equals 1.8 degrees Fahrenheit.
  • Kelvin is calculated as °C + 273; all Kelvin values are positive, starting at absolute zero (0 K = –273°C).

Energy and Calorie Definition

  • Heat is a form of energy measured in calories.
  • One calorie is the energy needed to raise the temperature of 1 gram of water by 1°C.
  • Different substances require different amounts of energy to raise their temperature—this is called specific heat.

Specific Heat

  • Specific heat is the amount of energy needed to raise the temperature of 1 gram of a substance by 1°C.
  • Water’s specific heat is 1 cal/g°C; copper’s is 0.092 cal/g°C.
  • Specific heat serves as a conversion factor between energy and temperature change.

Calculating Energy Using Specific Heat

  • The energy (in calories) required to heat a substance:
    heat = mass × specific heat × temperature change (ΔT).
  • Example: Heating 1000 g of water from 20°C to 50°C requires 30,000 calories.

Calorimetry and Food Calories

  • A calorimeter measures the energy content (calories) of food by burning it and heating water.
  • The equation used: calories released = mass of water Ă— specific heat Ă— (final temp – initial temp).
  • Food labels in the U.S. use "nutritional Calories" (capital C), where 1 Calorie = 1000 calories (1 kilocalorie).
  • Example: Burning half a bagel heats 1000 g water from 22°C to 92°C, releasing 70,000 calories = 70 nutritional Calories = 70 kilocalories.

Food Energy Content

  • 1 g carbohydrate = 4 kilocalories (nutritional Calories)
  • 1 g protein = 4 kilocalories
  • 1 g fat = 9 kilocalories
  • Example: Whole milk (12 g carbs, 9 g fat, 9 g protein):
    • Carbs: 12 Ă— 4 = 48 kcal
    • Fat: 9 Ă— 9 = 81 kcal
    • Protein: 9 Ă— 4 = 36 kcal
    • Total = 165 kcal

Key Terms & Definitions

  • Calorie (cal) — Energy to raise 1 g water by 1°C.
  • Specific Heat — Energy required to raise 1 g of a substance by 1°C.
  • Calorimeter — Device for measuring energy content of food by heat transfer.
  • Nutritional Calorie (Cal) — 1,000 small calories (1 kcal); used on food labels.
  • Kelvin (K) — SI unit for temperature; absolute zero is 0 K.

Action Items / Next Steps

  • Practice calculating calories using specific heat equations.
  • Review energy content conversion for carbohydrates, proteins, and fats.
  • Complete any assigned calorimetry problems or readings.

Full transcript