posted by Rachel .
A 0.6-g peanut is burned beneath 50 g of water, which increases in temperature from 22degreesC to 50 degreesc. What is the exact food value of the peanut? (Assuming a 40% efficiency)
heat to water = mass x specific heat x delta T.
mass of water = 50 g in the problem.
specific heat water = 1 calorie/gram*C
delta T = 50-22 = 28 degrees.
Calculate heat produced by the peanut to heat the water. Let's call that value x.
If the process was only 40% efficient, then
x/0.40 = all of the heat produced which we will call ??. That is the food value of the peanut.
Now here you can get into an argument since what I have calculated is the number of calories for the 0.6 g peanut. My calculations give a value of about 5800 calories OR about 5.8 kilocalories. (you need to do the exact math). Why the argument? Many foods, in calorie tables, show the calorie content as kilocalories BUT (and this is an important BUT) they call it calories. When your problem says to list the EXACT FOOD VALUE of the peanut, it makes me think they want the so-called BIG calorie and that is the kilocalorie so I would list 5.8; however, about 5800 calories is the correct answer. You may have a multiple guess answer sheet and that may be of some help in knowing what answer they want.