SCH 4U Energy Test Name: Multiple Choice (12 K) Identify the letter of the choice that best completes the statement or answers the question.
1. An exothermic reaction is one where a. heat is transferred from the surroundings into a system b. heat is transferred from a system into the surroundings c. kinetic energy is transformed into potential energy d. there is no transfer of heat e. none of the above
2. In an exothermic reaction, heat flows into the surroundings because a. the potential energy of the chemicals increases b. the kinetic energy of the chemicals decreases c. the chemical potential energy is converted into heat energy d. the chemical kinetic energy is converted into heat energy e. none of the above
3. A chemical system in which both energy and matter can flow into or out of a system is described as: a. a closed system d. a chemical system b. an open system e. none of the above c. an isolated system
4. Which of the following is not a form of kinetic energy in a chemical system? a. moving electrons within an atom b. the vibration of atoms connected by chemical bonds c. the rotation of molecules that make up the chemical system d. the translation of molecules within the chemical system e. the energy of protons and neutrons in atomic nuclei
5. The specific heat capacity of a substance is a. the quantity of heat required to raise the temperature of one mole of a substance by one degree Celsius or Kelvin b. the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius or Kelvin c. the quantity of heat required to raise the temperature of one molecule of a substance by one degree Celsius or Kelvin d. the quantity of heat required to raise the temperature of a substance by one degree Celsius or Kelvin e. none of the above 6. An enthalpy change is: a. the difference in the kinetic energy of the reactants and the products in a chemical change b. the difference in the potential energy of the reactants and the products in a chemical change c. the difference in enthalpies of the reactants and the products in a chemical change d. the sum of the potential and kinetic energies of the products e. the sum of the potential and kinetic energies of the reactants 7. We can communicate the energy changes obtained from empirical studies by: a. including an energy value as a term in the thermochemical equation b. writing a chemical equation and stating its enthalpy change c. stating the molar enthalpy of a specific reaction d. drawing a chemical potential energy diagram e. any of the above
8. Which statement concerning the Law of Conservation of Energy is not true? a. it applies to all chemical changes b. it involves all different forms of energy c. it applies to nuclear reactions d. it includes potential energy e. it involves heat content of substances
9. The molar heat of vaporization of water is 42 kJ/mol. How much energy is released by the condensation of 3.0 g of water? a. 0.88 kJ d. 250 kJ b. 7.0 kJ e. 0.07 kJ c. 130 kJ
10. What is another way to write the following equation?
2 C2H6(g) C2H2(g) + 2H2(g) ∆H = 3.2 10 kJ/mol
2 a. C2H6(g) C2H6(g) + 2H2(g) + 3.2 10 kJ 2 b. C2H6(g) + 3.2 10 kJ C2H2(g) + 2H2(g) 2 c. 2H2(g) + C2H2(g) + 3.2 10 kJ C2H6(g) 2 d. C2H6(g) – 3.2 10 kJ C2H2(g) + 2H2(g) e. none of the above
11. When solid ammonium chloride, NH4Cl, is added to water, the temperature of the solution decreases. Which statement best describes this observation? a. The reaction is exothermic b. Heat is released from the system, so it feels cooler. c. NH4Cl(s) + H2O(l) NH4Cl(aq) + 33.6 kJ d. NH4Cl(s) + H2O(l) NH4Cl(aq) H = +33.6 kJ e. NH4Cl(s) does not dissolve in water. 12. Which statement concerning the accompanying diagram is true?
a. H is positive b. the system is endothermic c. the system releases heat to the surroundings d. the heat content of the reactants is less than the heat content of the products e. the enthalpy of the products is greater than the enthalpy of reactants
Matching (10 A)
Match these thermochemical terms with the following statements. a. thermal energy h. open system b. chemical system i. isolated system c. surroundings j. closed system d. heat k. calorimetry e. exothermic l. bomb calorimeter f. enthalpy change m. endothermic g. temperature n. molar enthalpy ____ 13. all matter around a system that is capable of absorbing or releasing thermal energy ____ 14. amount of energy transferred between substances ____ 15. a system in which energy can move in or out, but not matter ____ 16. energy available from a substance as a result of the motion of its molecules ____ 17. releasing thermal energy as heat flows out of the system ____ 18. an ideal system in which neither matter nor energy can move in or out ____ 19. average kinetic energy of the particles in a sample of matter ____ 20. a system in which both matter and energy can move in or out ____ 21. the difference in enthalpies of reactants and products during a reaction ____ 22. the enthalpy change involving one mole of a substance Short Answer
23.Explain why
(3A)
24. Describe Hess's Law in your own words and include an example.
(2K)
25. What are the three simplifying assumptions often used in calorimetry?
(3K)
26. A kilogram of water and a kilogram of sand are at the same temperature. Do the two substances contain the same amount of heat energy? Explain.
(3A)
Problems
27. If an iron ring with a mass of 5.5 g changes temperature from 25.0ºC to 28.0ºC, how much energy has it absorbed?
(3A) 28. Ethanol, C2H5OH, is made industrially by the reaction of water with ethylene, C2H44. Calculate the value of Ho for the reaction
C2H4(g) + H2O(l) C2H5OH(l)
given the following thermochemical equations:
o C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O(l) H = –1411.1 kJ
o C2H5OH(l) + 3 O2(g) 2 CO2(g) + 3 H2O(l) H = –1367.1 kJ
(5)
29. From ∆Hdata for the formation of CO2(g) and H2O(l), and the thermochemical equation for the combustion of glucose,
C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(g)
∆HCO2(g) = - 393.5 ∆HH2O(g) = - 242 ∆H= -2.82 x 103 estimate ∆Hfor glucose, in kilojoules per mole.
(5)
SCH 4U Energy Test Answer Section
MULTIPLE CHOICE
1. ANS: B REF: K/U OBJ: 5.1 LOC: ECV.01 2. ANS: C REF: K/U OBJ: 5.1 LOC: ECV.01 3. ANS: B REF: C OBJ: 5.1 LOC: EC2.01 4. ANS: E REF: K/U OBJ: 5.1 LOC: EC1.05 5. ANS: B REF: K/U OBJ: 5.1 LOC: EC2.01 6. ANS: A REF: K/U OBJ: 5.1 LOC: EC2.01 7. ANS: E REF: K/U OBJ: 5.3 LOC: EC2.02 8. ANS: C REF: K/U OBJ: 5.2 LOC: EC1.02 9. ANS: B REF: I OBJ: 5.2 LOC: EC2.03 10. ANS: B REF: C OBJ: 5.3 LOC: EC2.02 11. ANS: C REF: C OBJ: 5.3 LOC: EC1.05 12. ANS: D REF: K/U OBJ: 5.3 LOC: EC2.03
MATCHING
13. ANS: C REF: K/U OBJ: 5.1 LOC: EC2.01 14. ANS: D REF: K/U OBJ: 5.1 LOC: EC2.01 15. ANS: J REF: K/U OBJ: 5.1 LOC: EC2.01 16. ANS: A REF: K/U OBJ: 5.1 LOC: EC2.01 17. ANS: E REF: K/U OBJ: 5.1 LOC: EC2.01 18. ANS: I REF: K/U OBJ: 5.1 LOC: EC2.01 19. ANS: G REF: K/U OBJ: 5.1 LOC: EC2.01 20. ANS: H REF: K/U OBJ: 5.1 LOC: EC2.01 21. ANS: F REF: K/U OBJ: 5.2 LOC: EC2.01 22. ANS: N REF: K/U OBJ: 5.2 LOC: EC2.01
SHORT ANSWER
23. ANS: Due to the Law of Conservation of Mass, the total amount of energy in the system must remain constant; consequently, the enthalpy change of the system must be equal in magnitude, but opposite in sign to the energy released to or absorbed from the surroundings.
REF: K/U OBJ: 5.1 LOC: EC2.02 24. ANS: Hess's law is a method of determining the enthalpy of a 'target' reaction from two or more reactions for which the enthalpy change is known. By adding the enthalpy changes of the known reactions, the enthalpy of the 'target' reaction can be calculated. Example: REF: C OBJ: 5.4 LOC: EC1.02 25. ANS: - no heat is transferred between the calorimeter and the outside environment - any heat absorbed or released by the calorimeter materials, such as the container, is negligible - a dilute aqueous solution is assumed to have a density and specific heat capacity equal to that of pure water
REF: C OBJ: 5.2 LOC: EC2.03 26. ANS: No. Since the water and sand have very different heat capacities, they would contain significantly different amounts of heat energy.
REF: I OBJ: 5.2 LOC: EC2.01
PROBLEM
27. ANS:
m = 5.5 g c = 0.444 J/gºC T = 28.0ºC – 25.0ºC = 3.0ºC q = mcT = (5.5 g)(0.444 J/gºC)(3.0ºC) = 7.3 J
7.3 J of energy has been absorbed.
REF: I OBJ: 5.1 LOC: EC2.03 28. ANS:
a.
13.8 MJ of energy is required to heat the water in the hot water tank. b.
Approximately $67 would be saved over the course of the year on the hot water tank.
REF: I OBJ: 5.1 LOC: EC3.01 29. ANS: Show the addition of equations to give "target" reaction
o C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O(l) H = –1411.1 kJ
o 2 CO2(g) + 3 H2O(l) C2H5OH(l) + 3 O2(g) H = +1367.1 kJ ______
o C2H4(g) + H2O(l) C2H5OH(l) H = –44 kJ
The Ho for the reaction is 44 kJ.
REF: I OBJ: 5.4 LOC: EC2.04 30. ANS: Determine equation for thermite reaction:
Rearrange given equations to add to add to target equation
The H the reaction is –848 kJ.
REF: I OBJ: 5.4 LOC: EC2.04
ESSAY
31. ANS: Advocates: - has low uranium fuel costs, including transportation - causes very little air pollution, such as green house and acid gases - reduces our dependence on fossil fuels for electricity generation, allowing those materials to be used for other purposes. Opponents: - the possible release of radioactive materials in a reactor malfunction - the difficulty of disposing of the highly toxic radioactive wastes - the large capital costs of building nuclear reactors and then decommissioning them at the end of their relatively short lifetime - unknown health effects of long-term low level exposure to radiation - thermal pollution from cooling water
REF: I OBJ: 5.6 LOC: EC3.01