TYPES OF CALORIMETRY PROBLEMS: I. Calculating the specific ...

TYPES OF CALORIMETRY PROBLEMS:
I. Calculating the specific heat of a metal q metal = - [ q H2O + q cal ]
m . s . ∆T = - [ (m . s . ∆T) + (C cal . ∆T) ]
Ex: A 44.0 g sample of an unknown metal at 99.0 • C was placed in a constant-pressure calorimeter
containing 80.0 g of water at 24.0 • C. The final temperature of the system was found to be 28.4 • C.
Calculate the specific heat of the metal. The heat capacity of the calorimeter is 12.4 J/ • C.
II. Using calorimetry data to calculate ∆H • rxn
1. Use calorimetry data to calculate q rxn . q rxn = - [ q H2O + q cal ]
q rxn = - [ (m . s . ∆T ) + (C . cal ∆T) ]
2. Calculate q rxn/g, q rxn/mole, or ∆H • rxn
Ex: O.5521 grams of pentane (C 5 H 12 ) was combusted in a bomb calorimeter filled with 1000.0 g of water and an
excess of O 2 according to the following equation:
C 5 H 12 (l) + 8 O 2 (g) ----------> 5 CO 2 (g) + 6 H 2 O (l)
(a) If the heat capacity of the calorimetry was 1,800.0 J/ • C and the temperature of the calorimeter and water rose
from 21.22 • C to 25.70 • C, what is the q rxn .
(b) Calculate the heat released per gram of pentane.
(c) Calculate ∆H • comb.

III. Using ∆H • rxn (or ∆H • /g of ∆H • /mol) to figure out calorimetry data.
1. Use ∆H • rxn (or q rxn /g or q rxn /mole) to calculate q rxn .
2. Plug q rxn into calorimeter expression and solve for whatever....T i , T f , ∆T, C cal
q rxn = - [ q H2O + q cal ]
q rxn = - [ (m . s . ∆T ) + (C cal . ∆T) ]
Ex: 0.600 g of B 5 H 9 (s) was combusted in a calorimeter containing 1,000.0 g of H 2 O. Predict ∆T
of water. Ccal = 1760 J/•C.
2 B 5 H 9 (s) + 12 O 2 (g) ----> 5 B 2 O 3 (g) + 9 H 2 O (l) ∆Hrxn = -9080 kJ