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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: maroy on March 13, 2011, 06:26:45 PM

Title: Food calorimetry
Post by: maroy on March 13, 2011, 06:26:45 PM
We burned a cheezies (2g) under a test tube and the heat combustion was funneled to heat up the water in the test tube.
Here are the data:
water : 15 ml = 15 g
temperature : from 20 to 28 C = a delta of 8 Celsius

Calculation:
Heat transferred to the water = mcT = (15g)(4.19 j/gC)(8C) = 503 J = 0.503 kJ
Heat coming from the cheezies = 0.503kJ = 0.503kJ/4.18kJ/Cal = 0.12 Calories
25 cheesies = 25(0.12 Cal) = 3 Cal

The bag says 300 Cal (25 cheezies)
Can someone explain why I am so off. Experimentally, I found 3 Cal instead of 300 Cal, a factor of 100.

Thank you,
Title: Re: Food calorimetry
Post by: enahs on March 13, 2011, 07:11:11 PM
Two things. Your conversion from kJ to calories is wrong.

Also, thermodynamic calories and nutritional calories are different. There are 1000 thermodynamic calories for every 1 nutritional calories.
Title: Re: Food calorimetry
Post by: maroy on March 13, 2011, 10:56:57 PM
Two things. Your conversion from kJ to calories is wrong.

Also, thermodynamic calories and nutritional calories are different. There are 1000 thermodynamic calories for every 1 nutritional calories.

1) why do you my conversion my conversion fron kJ to calories is wrong? the factor is 4.19 no?
2) the conversion from thermodynamic to nutritional os 1000... this what I am doing!!!
Title: Re: Food calorimetry
Post by: rabolisk on March 13, 2011, 11:47:06 PM
It seems right to me...
Title: Re: Food calorimetry
Post by: enahs on March 14, 2011, 12:12:55 AM
Yeah, I was remembering the direct conversion to the other calorie units. Just the thermodynamic .vs. food calorie.
Title: Re: Food calorimetry
Post by: maroy on March 14, 2011, 05:33:16 PM
I hope I could find the problem of my experiment. It should work!