1. Thermo-physical properties 2. Radiation properties - nptel - Indian ...

Mechanical Measurements Prof S.P.Venkatesan
Indian Institute of Technology Madras
Example 6
In a subsequent experiment, the calorimeter of Example 5 is used to determine
the heating value of sugar. A pellet of sugar weighing 0.303 g is burnt and the
corresponding temperature rise indicated by the calorimeter is 3.99°C. What is
the heat of combustion of sugar?
Figure 14 shows the variation of temperature of the calorimeter during the
experiment. Since heat losses are unavoidable the temperature will start
reducing as shown in the figure. By using ΔT as shown in the figure the effect of
the heat losses may be accounted for. Note that the work due to stirrer may itself
compensate for the heat loss to some extent. The slope of the cooling curve
takes this into account naturally.
Molecular formula for sugar is C12H22O11. The molecular weight of sugar is found
as
Molecular weight = 12.011× 12 + 1.008× 22 +
15.9995× 11
= 342.3 g / mol
C H2
The mass of sugar pellet of 0.303 g corresponds to
The heat release in the calorimeter is calculated based on
C = 1.2538 kJ / ° C
as
Q =−CΔ T =− 1.2538× 3.99 =−5.003
kJ
The combustion reaction for sugar is given by
O
0.303
0.000885 mol
342.3 =
T 3.99 C
Δ = ° and