Download Calorimetry Key - Iowa State University

Calorimetry
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
Chem 177 (BC)
Dr. Irmi
10/10/13
1. Heat Capacity (C) represents the amount of heat required to raise a given amount of a
substance 1 K.
2. (a) In your own words, what is the difference between Molar Heat Capacity and
Specific Heat? (b) Write out the equation for each.
Cm = q/ΔT = Joules/mole
Cs = q/ΔT = Joules/gram
3. When H2 (g) and O2 (g) react to form H2O (l), heat is released to the surroundings.
Consider the reverse reaction, namely, the formation of H2 (g) and O2 (g) from H2O (l).
a. Is this reaction exothermic or endothermic? (Circle one)
4. Given the following information, circle the term that best completes the statement.
Ag2O(s)  2 Ag(s) + ½ O2(g)
ΔH° = 31.05 kJ
a. Heat is released/absorbed.
b. The reaction is exothermic/endothermic.
c. Products/reactants have higher enthalpy content than products/reactants.
5. Two solid objects, A and B, are placed in boiling water and allowed to come to
temperature there. Each is then lifted out and placed in separate beakers containing 1000
g water at 10.0 °C. Which object has the larger heat capacity given:
a. Object A increases the water temperature by 3.50 °C.
b. Object B increases the water temperature by 2.60 °C.
Object A
6. The specific heat of NH3 (l) is 4.382 J/g-K. Calculate the heat required to raise the
temperature of 1.50 g of NH3 (l) from 213 K to 218 K.
q = m Cs ΔT
q = 1.5 (4.381) (218-213) = 33 J
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7. 0.800 g of sulfur is combusted to form SO2. All of the heat evolved is used to raise the
temperature of 100.0 g of water by 17.8 K. (a) Write the combustion reaction for sulfur.
(b) Calculate the heat of combustion of 1 mol of sulfur.
(a) S(s) + O2(g) → SO2(g)
(b) qcomb = -qwater = m Cs ΔT = 100 (4.184) (17.8) = 7450 J
(-7.45 kJ/0.80 g) (32 g/ 1 mol) = -298 kJ/mol
8. A 1.05g sample of benzoic acid is combusted completely in a bomb calorimeter.
Calculate the temperature change given that the heat capacity of the calorimeter is 1.80
kJ/K and the heat of combustion of benzoic acid is -26.4 kJ/g.
Q = ΔH X m = =26.4 (1.05) = -27.7 kJ
q = -C ΔT = -27.7 = - (1.80) ΔT
ΔT = 15.4 K
9. Given the chemical equation S(s) + O2(g)  SO2(g) ΔH = -297.1 kJ/mol, how much
heat is associated with the formation of 7.99 g of SO2(g)?
(7.99 g) (1 mol/ 64.06 g) (-297.1 kJ/ 1mol) = -37.1 kJ
Use this space to create and answer a test question based on what we talked about today.