Lecture Notes: Units of Measurement, Temperature, and Energy

Overview of Units of Measurement

  • Definition and significance of units of measurement in calculations.

  • Major types of measurement systems: English, metric, and International System of Units (SI).

  • Review of mass (grams), distance (meters), and volume (liters).

Temperature Measurement

  • Units of temperature:

    • English system: Degrees Fahrenheit (°F)

    • Metric system: Degrees Celsius (°C or Centigrade)

    • SI system: Kelvin (K)

  • Conversions between Celsius and Kelvin:

    • Formula for conversion:

    • From Celsius to Kelvin: (K = °C + 273)

    • From Kelvin to Celsius: (°C = K - 273)

  • Practical application of temperature in lab: Use Celsius and Kelvin only; no need to convert between Fahrenheit and Celsius.

  • Example conversion: 303 K to °C:

    • Calculation: (303 - 273 = 30) °C

Energy Measurement

  • Units of energy:

    • Metric system: Calorie

    • English system: British Thermal Units (BTUs)

    • SI system: Joule (J)

  • Definition of calorie:

    • One calorie is the amount of energy required to raise the temperature of 1 gram of water by 1°C.

  • Important distinction:

    • Nutritional calories (Cal) defined as 1 kcal = 1,000 scientific calories.

    • Nutritional calorie example: 60 kcal in a slice of bread.

Specific Heat Capacity

  • Specific heat:

    • Different substances require different amounts of energy to raise their temperatures.

    • Example comparisons:

    • Water: 1 calorie/g/°C

      • Requires 1 calorie to raise 1 g of water from 14°C to 15°C.

    • Copper: 0.09 calories/g/°C

      • Requires less energy compared to water.

Calorimetry and Energy Measurement

  • Calorimeter usage:

    • Device used to measure calories by burning food and measuring the temperature change in surrounding water.

  • Calculating heat absorption:

    • Heat absorbed by water calculated using:

    • Q = m imes c imes riangle T

      • Where:

      • Q = heat absorbed (calories)

      • m = mass of water (g)

      • c = specific heat of water (1 cal/g/°C)

      • riangle T = temperature change (°C)

      • Example: Calculate calories absorbed by 135 g of water changing temperature from 21.5°C to 38.8°C:

      • riangle T = 38.8 - 21.5 = 17.3°C

      • Calculation: Q = 135 g imes 1 cal/g/°C imes 17.3°C = 2335.5 ext{ calories}

      • Significant figures: Round 2335.5 to 2336 calories or 2.336 kcal.

Nutrition and Energy Yield in Foods

  • Energy content in macronutrients:

    • Protein: 4 kcal/g

    • Carbohydrates: 4 kcal/g

    • Fats: 9 kcal/g

  • Example calculation for a piece of salmon with:

    • Protein: 51 g

    • Fat: 15 g

    • 51 g imes 4 rac{kcal}{g} = 204 ext{ kcal}

    • 15 g imes 9 rac{kcal}{g} = 135 ext{ kcal}

    • Total energy = 204 + 135 = 339 kcal

Classification of Matter

  • Elements: Simplest forms of matter (e.g., hydrogen, oxygen), listed by chemical symbols (1-2 letter abbreviations).

  • Pure substances: Atoms (e.g., hydrogen) and compounds (e.g., water) as defined by distinct properties and composition.

  • Mixtures:

    • Homogeneous mixtures: Uniform composition (e.g., Gatorade).

    • Heterogeneous mixtures: Distinguishable components (e.g., sand and water).

Physical vs. Chemical Changes

  • Physical changes: Do not alter the chemical structure (e.g., ice melting to water).

  • Chemical changes: Involve chemical reactions altering the substance's composition (e.g., rusting of iron).

  • Examples of changes in water: solid (ice) to liquid (water) to gas (water vapor); always remains H2O.

Summary Points

  • Distinguish between specific heat as a property of substances.

  • Use calorimetry for measuring energy content in food.

  • Convert between types of energy measurements (calories to kilocalories and nutritional calories).

  • Understand the classification and definitions of elements and compounds in the periodic table, along with simplifications in energy understanding in nutrition.