Transcript E. Calorimetry

E. Calorimetry
q = m • C • T
qsys = - qsurr
q = heat or enthalpy
m = mass
C = specific heat
 T = temperature change
J
g
J/g°C
°C
Note – these problems could also be done in calories
Quantity of heat supplied
q
Specific Heat Capacity or Specific Heat (C) 
m  T
Tells how much heat is
required to change the
temp of a substance.
Some specific heats are
Al
0.902 J/g oC
Cu
0.385 J/g oC
H2O 4.184 J/g oC
Temperature change
(always Tf-Ti)
• A 55.0 g piece of metal was heated in
boiling water to a temperature of 99.8oC
and dropped into an insulated beaker with
225 mL of water (d = 1.00 g/ml) at 21.0 oC.
The final temperature of the metal and
water is 23.1oC. Calculate the specific heat
of the metal assuming that no heat was lost
to the surroundings.
1. Pressure Constant (Coffee Cup)
Calculate Hrxn in kJ/mol when mixing:
50 mL of 0.10M AgNO3
50 mL of 0.10M HCl in a coffee cup calorimeter.
The temperature rises from 22.3 °C to 23.1 °C.
AgNO3(aq) + HCl(aq)  AgCl(aq) + HNO3(aq)
2. Volume Constant (Bomb Calorimeter)
qrxn = - Cbomb • T
Cbomb is an
experimentally
determined value
using a known
material.
Each calorimeter has
its own constant value!!
2. Volume Constant (Bomb Calorimeter)
• Octane, C8H18, a primary constituent of gasoline, burns in air.
2 C8H18(l) + 25 O2(g)  16 CO2(g) + 18 H2O(l)
• Suppose that a 1.00 g sample of octane is burned in a
calorimeter that contains 1.20 kg of water. The temperature of
the water and the bomb rises from 25.00oC to 33.20oC. If the
specific heat of the bomb, Cbomb, is known to be 837 J/oC,
calculate the molar heat of reaction of C8H18.