Wednesday, May 07, 2014

Specific Heat Capacity of Chocolate

Good ol' physics. So many people questioned why I would take physics when all of my interest lies in cooking and baking. "What are you going to calculate? The velocity of your cake as it hits the floor? Will you have enough time to rescue it?" First of all, I don't plan on dropping any cakes. Second of all, whether physics is used in baking or not (it actually is, just not extensively), I can take physics if I would like to, it doesn't have to apply to my field of interest, as long as it interests me personally. 

I recently did a physics-related experiment in thermodynamics, though I suppose it could also be argued as more of a chemistry experiment in thermochemistry. Anyways, I was attempting to find the specific heat capacities of different types of chocolate. My prediction was that the darker the chocolate, the higher the specific heat capacity would be, and therefore it would take more time or energy to melt darker chocolate. 

The specific heat capacity of a substance is the quantity of energy (in joules) required to change the temperature of one gram of a substance by 1°C. I tested the specific heat capacity of four different types of chocolate in three trials each: 50% cocoa, 70% cocoa, 85% cocoa, and 90% cocoa (90% is my favorite). I found the specific heat capacity by recording the temperature change of 10.0 grams of each type of chocolate using a digital instant-read thermometer as it melted in a double boiler with the water below held at a constant 91.0°C over a period of three minutes. Then I used the formula q = cmΔT, where q is the heat provided by the double broiler, c is the specific heat capacity of the chocolate (the unknown), m is the mass of the chocolate, and ΔT is the temperature change of the chocolate.

The result? Why don't I wait and share that tomorrow....


Anonymous said...

What value did you use for q, the heat from the double boiler?

Bexy said...

I used 1770 kJ as the value of q.

I calculated this by
Using average values:
qstove = cm ΔT
qstove = (4.184J/g°C) (10.0g) (42.2)
qstove = 1770 kJ

Where 42.2 degrees Celsius was found to be the average temperature change of the water.