Download Chapter 11 Homework

Thermochemistry
Chapter 11 Assignment & Problem Set
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Thermochemistry
Chapter 11 Assignment & Problem Set
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Study Guide: Things You Must Know
Vocabulary (know the definition and what it means):
 heat (thermal energy)
 temperature
 chemical potential energy
 thermochemistry
 conservation of energy
 system vs. surroundings
 endothermic
 exothermic
 joule
 specific heat (capacity)
 calorimetry
 calorimeter
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enthalpy
thermochemical equation
heat of reaction
heat of combustion
heat of solution
heat of fusion
heat of solidification
heat of vaporization
heat of condensation
heating and cooling curves
Honors: standard heat of formation
Learning Objectives:
 heat is a form of energy (thermal energy) that flows between objects at different temperatures.
 heat is different than temperature, which is a measure of average kinetic energy.
 chemical potential energy is a form of energy stored within a substance, depending on the types of atoms,
bonds, and attractive forces of that substance.
 thermal energy can be exchanged between substances, and thermal energy and chemical potential can be
exchanged.
 energy can change forms, however it is conserved in every process or chemical reaction.
 how to designate the “system” and “surroundings” in a process or chemical reaction.
 if a system gives off heat it is called exothermic, and the sign of heat (q or H) is negative because the
system loses energy to the surroundings.
 if a system absorbs heat it is called endothermic, and the sign of heat (q or H) is positive because the
system gains energy from the surroundings.
 a joule (J) is the metric unit for heat and energy.
 how to solve problems using the specific heat equation.
 calorimetry is the precise measure of heat in a process or chemical reaction.
 calorimetry is performed in a closed thermal system call a calorimeter.
 calorimetry is based on conservation of energy.
 thermochemical equations show the amount of heat absorbed or given off in a chemical reaction.
 how to solve problems involving thermochemical equations.
 heat of solution is the amount of heat absorbed or given off when a substance dissolves.
 heat is absorbed when a substance melts (heat of fusion) or boils (heat of vaporization).
 heat is given off when a substance freezes (heat of solidification) or condenses (heat of condensation).
 how to calculate total heat changes following a heating or cooling curve.
 Honors: how to calculate heat of reaction using standard enthalpy of formation (Hfo).
Key Reference Tables
 Table B: Physical Constants for Water
 Table D: Selected Units
 Table I: Heats of Reaction at 101.3 kPa and 298 K
 Table T: Important Formulas and Equations
Thermochemistry
Chapter 11 Assignment & Problem Set
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•Read Chapter 11: Thermochemistry. Skip the short parts on “Hess’s Law” and “Standard Heats of Formation” (pp
314-318). Honors section will not skip “Standard Heats of Formation” (pp 316-318).
•Lab 9: Specific Heat of a Metal
•Lab 10: Heat of Fusion
•Regents Tables:
Table B: Physical Constants for Water
Table D: Selected Units
Table I: Heats of Reaction at 101.3 kPa and 298 K.
Table T: Important Formulas and Equations
•Warm-ups and problems will be collected before you take the test. Answer all problems in the space provided.
For problems involving an equation, carry out the following steps: 1. Write the equation.
2. Substitute numbers and units. 3. Show the final answer with units. There is no credit without showing work.
Heat & Energy Units, and Endothermic & Exothermic
1. Make the following conversion:
a. 1.8 kJ to J
b. 4.5 x 10-2 kJ to J
2. Classify these processes as endothermic or exothermic:
a. condensing steam
b. evaporating ethanol
c. cooking a potato
d. melting ice
Specific Heat Capacity (Specific Heat)
3. How many joules of heat is required to warm 32.0 g water from 25.0oC to 80.0oC?
4. A piece of stainless steel weighing 1.55 g absorbs 141 J of heat when its temperature increases by 178oC. What
is the specific heat of the stainless steel?
5. What is the specific heat of a substance if it takes 890. J of heat to increase the temperature of 50. g of that
substance from 63oC to 85oC?
6. How much heat is required to raise the temperature of 250 g of mercury 52oC? (The specific heat of mercury is
0.14 J/g oC).
7. How many kilojoules of heat are absorbed when 1.00 L of water is heated from 18oC to 85oC?
Thermochemistry
Chapter 11 Assignment & Problem Set
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Calorimetry
8. A small pebble is heated and placed in a coffee-cup calorimeter containing 25.0 g of water at 25.0oC. The water
reaches a maximum temperature of 26.4oC. How much heat was released by the pebble?
9. 50. g of a heated copper bar is placed into 45 mL of water at 25oC and the temperature of the water rises to
29oC. How much heat was released by the copper?
Thermochemical Equations
10. What happens to the sign of H when the reverse of a chemical equation is written?
11. Given the reaction:
CaO(s) + H2O(l)  Ca(OH) 2(s)
H = -65 kJ.
Is this reaction exothermic or endothermic? How much heat is given off or absorbed when 320.g of Ca(OH)2 is
formed?
12. When carbon disulfide is formed from its elements, heat is absorbed. Calculate the heat absorbed when 5.66 g
of carbon disulfide is formed. Is this reaction endothermic or exothermic?
C(s) + 2S(s)  CS2(l) H = 89.3 kJ
13. Lithium bromide readily dissolves in water. Does the temperature of water increase or decrease when LiBr is
dissolved?
14. Write a balanced chemical equation for the complete combustion of propane (C3H8). How much heat is released
when 245 g of propane is burned?
15. Gasohol contains ethanol (C2H5OH), which when burned reacts with oxygen to form CO2 and H2O. How much
heat is released when 12.5 g of ethanol burns?
Thermochemistry
Chapter 11 Assignment & Problem Set
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16. The methanol “cannon,” shot off in class, reacts methanol (CH3OH) with oxygen to form CO2 and H2O. How
much energy is released when 2.53 g of methanol is burned in the cannon?
17. How much heat in kJ is released when 0.677 mol NaOH is dissolved in water?
18. How much heat is absorbed when 15 g of NaCl is dissolved in water?
19. Honors If 150. g of propane and 750. g of O2 undergo complete combustion, how much heat is released?
Heat of Fusion and Heat of Vaporization
20. Explain why ice melts at 0oC without an increase in temperature, even though heat is flowing from the
surroundings into the system (the ice). Is melting ice endothermic or exothermic?
21. How many grams of ice at 0oC and 101.3 kPa could be melted by the addition of 0.400 kJ of heat?
22. How much heat is absorbed when 63.7 g of water at 100oC is converted to steam at 100oC?
23. Honors An ice cube at 0oC was dropped into 30.0 g water in a calorimeter cup at 45.0oC. At the instant the ice
was melted, the temperature of the water in the cup was 19.5oC. What was the mass of the ice cube?
Thermochemistry
Chapter 11 Assignment & Problem Set
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24. How much heat is released when 325 g of steam at 100.oC condenses into water at 100.oC?
25. How much heat does it take to turn 400. g of water at 72oC into steam at 140oC? The specific heat of steam is
2.0 J/g oC. Draw the temperature vs. heat added diagram for this problem and label KE or PE for each segment
of the curve.
Heat of Formation
26. Honors What is standard the heat of formation of Cl2(g)?
27. Honors Use standard heats of formation and text Table 11.6 to calculate the heat of reaction for the
decomposition of hydrogen peroxide: 2H2O2(l)  2H2O(l) + O2(g)
28. Honors Use enthalpies of formation to calculate the heat of reaction for the complete combustion of methane.
Hof (CH4) = -74.9 kJ, Hof (H2O(l)) = -285.8 kJ, Hof (CO2) = -393.5 kJ
What is the percent error in your calculated value if the true value is -890.4 kJ?
Review
29. Write the molecular equation and the net ionic equations for the reaction of calcium chloride and silver nitrate.
30. How many grams of oxygen are formed by the decomposition of 25.0 g of hydrogen peroxide?
2H2O2(l)  2H2O(l) + O2(g)
31. What is the average atomic mass of carbon given the abundance and mass of its two isotopes: 98.9% is C-12
and 1.1% is C-13?