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Unformatted text preview: ;0 process is endothermic
∆H<0 process is exothermic CH4(g) + 2O2(g) Æ CO2(g) + 2H2O(g)
∆H = -802.3 kJ
2CH4(g) + 4O2(g) Æ 2CO2(g) + 4H2O(g)
∆H = -1604.6 kJ
CH4(g) + 2O2(g) Æ CO2(g) + 2H2O(l) ∆H = -890.4 kJ
∆H = 100.0 g CH4 x 1 mol CH4
= -5001.9 kJ ∆H is negative, so heat is released.
16.04 g CH4 1 mol CH4 Calorimetry
measurement of heat flow
heat capacity C =
amount of heat required to raise the temperature of a given
amount of a substance 1°C
Specific heat (s): amount of heat required to raise the temperature of 1 gram of a
substance 1°C (see table 6.1, pg 242)
q = sm∆T
heat flows are measured in a device called a calorimeter. In a coffee cup calorimeter, P
is constant and q = ∆H
16.69 g Fe is heated to 100.0° C and dropped into 100.0 g water initially at 15.0°C.
If the final temperature of the water is 16.5° C, calculate the specific heat of the Fe.
6-3 Chapter 6 Thermochemistry -qFe = qwater
-sm∆T(Fe) = sm∆T(water)
-s(16.69 g)(16.5° C - 100.0° C) = (4.18 J/g ° C)(100.0 g)(16.5° C - 15.0° C)
s = 0.45 J/g ° C
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