Calorimetry

Calorie Calorie: The amount of energy needed to raise the temperature of 1 g of pure water by 1ºC at atmospheric pressure Food calories are kilocalories (kcal) 1 kcal = 1000 calories Nutrition daily values (%DV) are based on a 2,000 calorie diet

Calorie content of food components Protein = 4 kcal/g Carbohydrates = 4 kcal/g Fat = 9 kcal/g (Alcohol = 7 kcal/g) Fiber is a carbohydrate but is not easily absorbed by our body, so it does not contribute as much energy

Calculating calorie content Calories from fat Calories from protein + Calories from carbohydrates _______________________________ = Total calories Calculating calories from… Fat: (g fat) x (9 cal/g fat) Protein: (g protein) x (4 cal/g protein) Carbohydrate: (g carb) x (4 cal/g carb)

Ex: Calculating calorie content Known: Total calories = 160 cal Total fat = 1 g Total protein = 3 g Fat = 9 cal/g Protein = 4 cal/g Carbohydrate = 4 cal/g

Ex: Calculating calorie content Calories from fat: 1 g fat x 9 cal/g fat = 1 x 9 = 9 calories Calories from protein: 3 g protein x 4 cal/g protein = 3 x 4 = 12 calories

Ex: Calculating calorie content 9 cal from fat 12 cal from protein + ?? cal from carbohydrate __________________________ 160 total calories 160 – 12 – 9 = 150 calories from carbohydrates

Ex: Calculating calorie content 150 calories from carbohydrates Carbohydrates: 4 cal/g 150 cal = (?? g carb.) x (4 cal/g) (150 cal) / (4 cal/g) = ?? g carb 150 / 4 = 37.5 g carb

Ex: Calculating calorie content 37.5 ≈ 40 g carbohydrates! Calculating calories from fat? Calories from fat = total calories – calories from protein – calories from carbohydrate cal from fat = 160 – 12 – 150 = 8 cal from fat

Calorimetry A constant-pressure calorimeter measures the change in enthalpy (∆H) of a reaction occurring in solution during which the atmospheric pressure remains constant Measure heat transfer to calculate energy content

Basis of calorimetry Measure temperature of a reaction mixture Reaction mixture is usually water containing the food Food may be directly in the water or in a test tube By measuring temperature, we can calculate the calorie content

Calorimetry calculations ∆H = m x Cp x ∆T ∆H = enthalpy = calorie content of food m = mass of food, in grams Cp = specific heat of solution (water Cp = 1 cal/g) ∆T = change in temperature of water