IB Chemistry III B1 presentation.

1. B1: ENERGY
B.1.1. Calculate the energy value
of a food from enthalpy of
combustion data

2. 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)

3. 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

4. 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

5. USE THE EQUATION Q = MC ΔT
 Ifasked 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 ***

6. EXAMPLE 1#

7. EXAMPLE 2

8. EXAMPLE 3

9. SOURCES
 http://www.fao.org/DOCREP/006/Y5022E/
y5022e04.htm
 http://www.chem.hope.edu/~polik/Chem345-2000/
bombcalorimetry.htm