FOOD ENERGY

Have you ever counted Calories?

Food energy is measured in Calories (upper case C)

It takes 1000 calories to make up a Calorie

Example: A standard French fry serving contains 220 Calories of food energy.How many calories are present?

220 Calories x 1000 cal/Cal. = 220,000 calories

It takes 1 calorie to raise the temperature of 1 g of water 1 CSimplified formula may be used: calories = grams of water x (final C – initial C)

This is determined by the burning of food under controlled conditions (CALORIMETRY) using an instrument called a calorimeter.

Pre-lab problem:

1. You want to raise the temperature of 250mL of water from 22 C to 99 C. How much heat energy will be needed?

Use equation calories = grams of water x (final C – initial C)

(250 g) x (77) = 19,250 calories = 19.25 Calories

EXPERIMENT: CALORIES IN A CHEESE PUFF

Hypothesis: We predict that there are _____fewer_____ Calories in a cheese puff than the number listed on the nutrition label.

DATA TABLE

½ Cheese Puff Sample

Mass (g) Temperature (C)

Original Final Change Original Final Change#1 1.1 0.6 0.5 28.6 34 5.6

#2

#3

Procedure

1. Obtain ½ a cheese puff. Record it’s mass (ORIGINAL).

2. Pour exactly 100 mL tap water into the aluminum can. Record the temperature of the water in the can (ORIGINAL).

3. Place the ½ cheese puff on the tab in the bottom can. Indicate with a RED CUP when ready for a teacher to ignite cheese puff. Immediately place the can filled with 100 mL of water over the burning puff.

4. Keep the thermometer inside the can, but make sure it is NOT touching the side or bottom.

5. Allow the puff to burn until it goes out.

6. Record the water’s highest temperature (FINAL).

7. Record the mass of charred puff (FINAL).

CALCULATIONS AND QUESTIONS

Answer these questions on a SEPARATE sheet of paper.

1. Calculate the calories of heat from the burning puff. The 100 mL water has a mass of 100 g (for all practical purposes the density of water is 1 gram/mL) and the specific heat of water is one calorie/degree Celsius/gram (1 calorie/gram °C = 4.186 joule/gram °C).

Use the following equation to make the calculation.

calories = (grams of water) x (temperature change) x (specific heat of water)

calories = (100g) x (34 °C – 28.6 °C) x (1 calorie/gram °C) = 540 calories

2. Divide the calories from question 1 by the change in mass of the puff. This determines the calories released per gram of puff burned. Record your answer in Kcal or Calories.

540 calories / (1.1 g – 0.6 g) = 1080 calories/g = 1.08 Calories/g

3. Multiply the measured Calories by the number of grams in a serving size, obtained from nutritional panel.

1.08 Calories/g x (28 g/14 cheese puffs) = 2.16 Calories/cheese puff

4. Compare your Calorie results to the nutritional panel.

150 Calories / 14 cheese puffs = 10.71 Calories/cheese puff > 2.16 Calories/cheese puff

5. Conclusion: There are _____fewer_____ Calories in a cheese puff than the number listed on the nutrition label.

6. Calculate your percent error.

(actual – measured Calories per serving) x 100 =actual Calories per serving

(5.36 – 1.08) x 100 = 79.85% (5.36)

7. Why do you suppose the calculated values for calories per gram are less than the actual value listed on the nutrition label? What could account for the difference? What are possible reasons for the inaccuracy?

Didn’t burn the entire cheese puff- had mass left over Burning cheese puff could have lost heat to air/surroundings instead of

transferring all heat energy directly to the water filled can Inaccurate temperature readings

Scaffolded summary of experiment:

The increase in the __temperature__ of the water shows that ___heat energy___ had been stored in the cheese puff, which was released while it burned. We can look at the change in ___heat/temperature___ of the water to find out how much ___heat energy___ is trapped/stored in a cheese puff (the change in enthalpy).