B1: ENERGYB.1.1. Calculate the energy value of a food from enthalpy of combustion data

USE THE EQUATION Q = MC ΔT

q = change in heat or energy (J)

m = mass (g)

c = specific heat (J/g ● K)

ΔT = change in temperature (K)

BOMB CALORIMETRY

The specific heat used will be that of water (about 4.184 J/g °C) because the reaction to find q will take place in a bomb calorimeter like the one pictured here

BOMB CALORIMETRY

The food is placed in the steel “bomb” where it is combusted

The ignition unit causes the combustion to occur within the bomb by heating up the sample

The thermometer measures the temperature increase as the reaction within the bomb occurs, the water absorbing the heat that is released

The stirrer ensures that the water’s temperature is staying the same within the dewar

USE THE EQUATION Q = MC ΔT

If asked to find the calories in the food (rather than Joules), convert q to calories by dividing the number of Joules by 4.184

The answer is generally in the form of J/g, kJ/g, J●g/mol, kJ●g/mol, cal/g, kcal/g, etc.

*** 1 cal = 4.184 J ***

EXAMPLE 1#

EXAMPLE 2

EXAMPLE 3

SOURCES

http://www.fao.org/DOCREP/006/Y5022E/y5022e04.htm

http://www.chem.hope.edu/~polik/Chem345-2000/bombcalorimetry.htm