Calculating Food Value of a Peanut Through Thermodynamics: Efficiency and Joules

[ashvuck101]

Homework Statement

6. Cameron burns a 0.5g peanut beneath 75g of water, which increases in temperature from 22 ºC to 40 ºC
a. Assuming 40% efficiency, what is the food value, in J, of the peanut?
b. What is the food value in J per gram?

Homework Equations

q=mCt

The Attempt at a Solution

i just wanted to know does question a mean i take 40% from the calculated joules?

 

[Chewy0087]

No, it's not, what it's saying to you is that the energy given off by the peanut to heat up the water is only 40% of the total energy given off in combustion, you need to work out the 100%. (was confused there for a sec :D)

 

[davieddy]

No. It means only 40% of the peanut's energy goes into the water

 

[ashvuck101]

what so how am i meant to calulate the other 60% that's not possible?

 

[Chewy0087]

Of course it's possible, that's like me saying to you;

You have 4 apples, which is 40% of the total number of apples from the bag, how many apples were in the bag?

 

[ashvuck101]

er could you put that to me algerbarically please... i mean it makes sense if it was 50% all you do is double it

 

[ashvuck101]

could it be .4x=(Joules calulated)?

 

[Chewy0087]

0.0

From 50% to 100% you times by 2...

From 40% to 100% you times by...

And ^ yes you're right.

 

[davieddy]

Of course it's possible, that's like me saying to you;

You have 4 apples, which is 40% of the total number of apples from the bag, how many apples were in the bag?

Beat me to it again.
Although I considered replying earlier
in similar vein I just couldn't bear to do it.

David

 

[Chewy0087]

lawl =D