Science Buddies: "Ask an Expert"

Hello, I am wondering if you can help me with my science fair project. I am trying to do my final research, and my project is due Monday. I need to know something: When I burn the food(for this project I am planning on using peanuts and marshmallows) on the needle, is the it taking the energy inside the marshmallow and turning it into heat energy? and the temperature of the water reveals the caloric balance? (:S)
Please respond ASAP!

Hi Kaybrie,

Yes, the chemical energy in the peanut or marshmallow gets turned into heat, which increases the temperature of the water. The change in the water's temperature reveals the amount of energy transferred:

Q = m*(Tf-Ti)*Cp

where Q is the energy transferred (which is what you are calculating), m is the mass of the water that was heated*, Tf is the final temperature of the water, Ti is the initial temperature of the water, and Cp is the heat capacity of water (4.184 joules/(gram K)). Note that the temperatures must be in Celsius or Kelvin; if you use degrees Fahrenheit, your calculations will be incorrect.

*this earlier incorrectly said the mass of the object that burned. Thank, bfinio, for correcting!

Post back if you have more questions.

Terik - one important correction - "m" in your formula would be the mass of the water, not the mass of the peanut or marshmallow. That equation gives the amount of heat it takes to raise a certain amount of a material (which has a physical property Cp) by a certain temperature. All four variables need to refer to the same material (in this case, water) - you can't mix and match them.

The amount of heat you get from burning a certain mass of food would be calculated using the heat of combustion:

http://en.wikipedia.org/wiki/Heat_of_combustion

-Ben