THERMOCHEMISTRY QUIZ Part VI

1. A coffee cup calorimeter initially contains 125 g of water, at a temperature of 24.2oC. Ammonium nitrate (NH4NO3, 7.07 g), also at 24.2oC, is added to the water, and the final temperature is 18.3oC. What is the heat of solution of ammonium nitrate in kJ/mol? The specific heat capacity of the solution is 4.18 J/oC g. (Ar N = 14, O = 16, H = 1).
a. 39.5
b. 37.3
c. 34.9
d. 32.2
e. 30.1
2. A 0.0500 L sample of 0.500 M barium nitrate is added to 0.0500 L of 0.500 M magnesium sulfate in a calorimeter whose total heat capacity is 455 J/oK. The temperature increase is 1.43oK. Calculate Ho in kJ for the following reaction.
Ba(NO3)2(aq) + MgSO4(aq) --> BaSO4(s) + Mg(NO3)2(aq)
a. -32.0
b. -30.0
c. -28.0
d. -26.0
e. -24.0
3. The combustion of 0.1584 g of benzoic acid increases the temperature of a bomb calorimeter by 2.54oC. The energy released by combustion of benzoic acid is 26.42 kJ/g. A 0.2130 g sample of vanillin (C8H8O3) is then burned in the same calorimeter. The temperature increases by 3.25oC. What is the energy of combustion (kJ/mole) of vanillin?
a. 3.22 x 103
b. 3.08 x 103
c. 2.74 x 103
d. 3.46 x 103
e. 3.82 x 103
4. When 2.62 g of lactic acid, C3H6O3, is burned in a calorimeter whose heat capacity is 21.7 kJ/oK, the temperature increases by 1.800oK. Calculate the heat of combustion of lactic acid in kJ per mole. (Atomic weights: C = 12, H = 1, O = 16).
a. 3.08 x 103
b. 1.68 x 103
c. 1.54 x 103
d. 1.48 x 103
e. 1.22 x 103
5. A 50.0 g piece of copper at 100oC is put into an insulated vessel containing 250 mL of water at OoC. What will be the final temperature (oC) of the water? The specific heat of water and copper are 4.18 J/goC and 0.385 J/goC respectively.
a. 50.0
b. 7.85
c. 5.62
d. 3.25
e. 1.87
6. The specific heat capacity of graphite is 0.71 J/oC g. How much heat energy (kJ) is required to raise the temperature of 850 g of graphite by 150oC?
a. 99
b. 91
c. 86
d. 75
e. 62
7. When 325 J of heat is added to 23.6 g of octane, C8H18, the temperature increases by 6.20oC. Calculate the molar heat capacity of octane (J/moleoC). (Ar C = 12, H = 1).
a. 288
b. 254
c. 235
d. 195
e. 179
8. A 50.0 g piece of copper at 100oC is put into an insulated vessel containing 250 mL of water at OoC. What will be the final temperature (oC) of the water? The specific heat of water and copper are 4.18 J/goC and 0.385 J/goC respectively.
a. 50.0
b. 7.85
c. 5.62
d. 3.25
e. 1.87
9. The specific heat capacity of graphite is 0.71 J/oC g. How much heat energy (kJ) is required to raise the temperature of 850 g of graphite by 150oC?
a. 99
b. 91
c. 86
d. 75
e . 62
10. When 325 J of heat is added to 23.6 g of octane, C8H18, the temperature increases by 6.20oC. Calculate the molar heat capacity of octane (J/moleoC). (Ar C=12, H = 1).
a. 288
b. 254
c. 235
d. 195
e. 179

THERMOCHEMISTRY QUIZ Part V

1. The combustion of B2H6 occurs according to the following equation. Using the enthalpies of formation, calculate the energy (kJ) released when 4.00 g of B2H6 reacts. (Ar B = 10.8, O = 16, H = 1).
B2H6(g) + 3 O2(g) --> B2O3(s) + 3 H2O(g)
Ho B2H6(g) = -57.4 kJ/mole;
Ho B2O3(s) = -1273 kJ/mole;
Ho H2O(g) = -241.8 kJ/mole
a. 1246
b. 1941
c. 522
d. 426
e. 281
2. Oxygen difluoride reacts with water according to the following equation. Using the enthalpies of formation, calculate the energy (kJ) released when 5.00 g of OF2 reacts.(Ar O = 16, F = 19, H = 1).
OF2(g) + H2O(g) --> O2(g) + 2 HF(g)
Ho H2O(g) = -241.8 kJ/mole
Ho HF(g) = -271.1 kJ/mole
Ho OF2(g) = +17.6 kJ/mole
a. 75.6
b. 62.5
c. 51.8
d. 29.4
e. 12.6
3. Nitroglycerin decomposes via the following process. Given the enthalpies of formation, calculate the energy liberated when 10 g of nitroglycerin is detonated. (Ar C = 12, H = 1, N = 14, O = 16).
4 C3H5(NO3)3(l) --> 6 N2(g) + O2(g) + 12 CO2(g) + 5 H2O(g)
Ho C3H5(NO3)3(l) = -364 kJ/mole
Ho CO2(g) = -393.5 kJ/mole
Ho H2O(g) = -241.8 kJ/mole
a. 196
b. 49
c. -3383
d. -4475
e. -4825
4. The fat, glyceryl trioleate, is metabolized via the following reaction. Given the enthalpies of formation, calculate the energy (kJ) liberated when 1.00 g of this fat reacts. (Ar C = 12, H = 1, O = 16).
C57H107O6(s) + 80 O2(g) --> 57 CO2(g) + 52 H2O(l)
Ho C57H107O6 = -70870 kJ/mole
Ho H2O(l) = -285.8 kJ/mole
Ho CO2(g) = -393.5 kJ/mole
a. 42.6
b. 40.4
c. 37.8
d. 33.4
e. 30.2
5. Using the enthalpies of formation, calculate the energy (kJ) released when 3.00 g of NH3 reacts according to the following equation. (Ar B = 10.8, O = 16, H = 1).
4 NH3(g) + 5 O2(g) --> 4 NO(g) + 6 H2O(g)
Ho NH3(g) = -46.1 kJ/mole
Ho NO(g) = +90.2 kJ/mole
Ho H2O(g) = -241.8 kJ/mole
a. 30.8
b. 34.3
c. 37.2
d. 39.9
e. 42.6
6. Calculate the Ho for the following reaction using the given bond energies.
(H - F = 565 kJ; O - O = 494 kJ; H - O = 463, O - F = 184).
F2O(g) + H2O(g) --> O2(g) + 2 HF(g)
a. -390
b. -360
c. -330
d. -260
e. -230
7. The enthalpy change for the following reaction is 368 kJ. Calculate the average O - F bond energy.
OF2(g) --> O(g) + 2 F(g)
a. 184
b. 242
c. 368
d. 536
e. 736
8. Calculate the Ho for the following reaction using the given bond energies.
(C - H = 414 kJ; F - F = 155 kJ; H - F = 431, C - F = 485).
CH4(g) + 4 F2(g) --> CF4(g) + 4 HF(g)
a. -1678
b. -1598
c. -1542
d. -1422
e. -1388
9. Calculate the Ho for the following reaction using the given bond energies.
(H - Cl = 431 kJ; O - O = 494 kJ; H - O = 463, Cl - Cl = 243).
4 HCl(g) + O2(g) --> 2 H2O(g) + 2 Cl2(g)
a. -169
b. -152
c. -139
d. -120
e. -102

THERMOCHEMISTRY QUIZ Part IV

1. The standard enthalpy of formation of propane, C3H8, is -103.6 kJ/mole. Calculate the heat of combustion of one mole of C3H8. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively.
a. 2220
b. 2060.0
c. 1856
d. 1721.2
e. -1939.1
2. The standard enthalpy of formation of methanol, CH3OH, is -238.6 kJ mole. Calculate the heat of combustion of one mole of CH3OH. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively.
a. 1300
b. 1142
c. 976
d. 854
e. 727
3. The heat of formation of CO2(g) is -394 kJ/mole and that of H2O(l) is -286 kJ/mole. The heat of combustion of C5H12 is -3534 kJ/mole. What is the heat of formation of C5H12?
C5H12(l) + 8 O2(g) --> 5 CO2(g) + 6 H2O(l)
a. -7220
b. -152
c. -108
d. +108
e. +152
4. Using the following information calculate the heat of formation of N2H4.
N2H4(l) + O2(g) --> N2(g) + 2 H2O(l)Ho = -622.4 kJ
Hof H2O(l) = -285.9 kJ/mole
a. +98.6
b. +90.4
c. +70.6
d. +50.6
e. +33.5
5. Using the following information calculate the heat of formation of Fe2O3.
Fe2O3(s) + 3 H2(g) --> 2 Fe(s) + 3 H2O(l) Ho = -35.5 kJ
Hof H2O(l) = -285.9 kJ/mole
a. -893.2
b. -822.2
c. -464.4
d. -393.4
e. -250.4
6. Using the following information calculate the heat of formation of CCl4.
CH4(g) + 4 Cl2(g) --> CCl4(g) + 4 HCl(g) Ho = -402 kJ
Hof CH4(g) = -74.85 kJ/mole; Hof HCl(g) = -92.30 kJ/mole
a. -132
b. -108
c. -54.0
d. +54.0
e. +132
7. The heat of formation of PCl3(g) is -287.0 kJ/mole. What is the heat of reaction for the following process?
2 PCl3(g) --> 2 P(s) + 3 Cl2(g)
a. -612.8
b. -306.4
c. +153.2
d. +306.4
e. + 612.8
8. Given the heat of reaction, Ho = -2029.7 kJ, and the indicated heats of formation, determine the heat of formation of NH4NO3(s) in kJ.
2 Al(s) + 3 NH4NO3(s) --> 3 N2(g) + 6 H2O(g) + Al2O3(s)
Hof H2O(g) = -241.8 kJ; Hof Al2O3(s) = -1675.7 kJ
a. +365.6
b. +298.2
c. -298.2
d. -365.6
e. -442.5
9. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively. Using the data for the following combustion reaction, calculate the heat of formation of C3H8(g).
C3H8(g) + 5 O2(g) --> 3 CO2(g) + 4 H2O(l) Ho = -2221.6 kJ
a. -143.3
b. -103.6
c. 20.4
d. 185.4
e. 212.2
10. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively. Using the data for the following combustion reaction, calculate the heat of formation of C3H4(g).
C3H4(g) + 4 O2(g) --> 3 CO2(g) + 2 H2O(l) Ho = -1939.1 kJ
a. -143.3
b. -103.8
c. 20.4
d. 185.4
e. 212.2

THERMOCHEMISTRY QUIZ Part III

1. Calculate the value of Ho/kJ for the following reaction using the listed thermochemical equations: 3 NO2(g) + H2O(l) --> 2 HNO3(l) + NO(g)
NH4NO3(s) --> N2O(g) + 2 H2O(l) Ho/kJ = -125.2 kJ
3 NO(g) --> N2O(g) + NO2(g) Ho/kJ = -155.8 kJ
4 NH3(g) + 5 O2(g) --> 4 NO(g) + 6 H2O(l) Ho/kJ = -1169.2 kJ
NO(g) + 12 O2(g) --> NO2(g) Ho/kJ = -56.6 kJ
a. -124.3
b. -95.6
c. -82.6
d. -71.4
e. -56.2
2. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction: B2H6(g) + 6 Cl2(g) --> 2 BCl3(g) + 6 HCl(g)
BCl3(g) + 3 H2O(l) --> H3BO3(g) + 3 HCl(g) Ho/kJ = -112.5
B2H6(g) + 6 H2O(l) --> 2 H3BO3(s) + 6 H2(g) Ho/kJ = -493.4
1/2 H2(g) + 1/2 Cl2(g) --> HCl(g) Ho/kJ = -92.3
a. +698.2
b. -360.7
c. -545.3
d. -698.2
e. -1376
3. Determine Ho/kJ for the following reaction using the listed enthalpies of reaction: CH4(g) + 1/2 O2(g) --> CO(g) + 2 H2(g)
CH4(g) + 2 O2(g) --> CO2(g) + 2 H2O(l) Ho/kJ = -802 kJ
CH4(g) + CO2(g) --> 2 CO(g) + 2 H2(g) Ho/kJ = +206 kJ
CH4(g) + H2O(g) --> CO(g) + 3 H2(g) Ho/kJ = +247 kJ
a. -25.5
b. -85
c. -92
d. -102
e. -143
4. Calculate the Ho for the following reaction using the listed thermochemical equations: C2H4(g) + H2(g) --> C2H6(g)
C2H4(g) + 3 O2(g) --> 2 CO2(g) + 2 H2O(l) Ho/kJ = -1410.9 kJ
C2H6(g) + 7/2 O2(g) --> 2 CO2(g) + 3 H2O(l) Ho/kJ = -1559.8 kJ
H2(g) + 1/2 O2(g) --> H2O(l) Ho/kJ = -285.8 kJ
a. +178.4
b. +136.9
c. -136.9
d. -178.4
e. -192.4
5. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction: 3 NO2(g) + H2O(l) --> 2 HNO3(l) + NO(g)
NH3(g) + HNO3(l) --> NH4NO3(s) Ho/kJ = -145.7
NH4NO3(s) --> N2O(g) + 2 H2O(l) Ho/kJ = -125.2
3 NO(g) --> N2O(g) + NO2(g) Ho/kJ = -155.8
4 NH3(g) + 5 O2(g) --> 4 NO(g) + 6 H2O(l) Ho/kJ = -1169.2
NO(g) + 1/2 O2(g) --> NO2(g) Ho/kJ = -56.6
a. -1291.6
b. -805.9
c. -685.9
d. -300.1
c. -70.4
6. Determine Ho/kJ for the following reaction using the listed enthalpies of reaction: N2H4(l) + 2 H2O2(g) --> N2(g) + 4 H2O(l)
N2H4(l) + O2(g) --> N2(g) + 2 H2O(l) Ho/kJ = -622.3 kJ
H2(g) + 1/2 O2(g) --> H2O(l) Ho/kJ = -285.8 kJ
H2(g) + O2(g) --> H2O2(l) Ho/kJ = -187.8 kJ
a. -864.3
b. -818.3
c. -745.6
d. -642.2
e. -604.3
7. Calculate the value of Ho/kJ for the following reaction using the listed thermochemical equations: 2 H2O2(l) 2 H2O(l) + O2(g)
2 H2(g) + O2(g) --> 2 H2O(g) Ho/kJ = -483.6 kJ
H2O(l) --> H2O(g) Ho/kJ = +44.0 kJ
H2(g) + O2(g) --> H2O2(l) Ho/kJ = -187.6 kJ
a. -208.4
b. -196.4
c. -188.4
d. -176.5
e. -164.2
8. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction:
4 C(s) + 8 H2(g) + 2 O2(g) --> 3 CH4(g) + CO2(g) + 2 H2O(l)
C(s) + 1/2 O2(g) --> CO(g) Ho/kJ = -110.54
CO(g) + 1/2 O2(g) --> CO2(g) Ho/kJ = -282.97
H2(g) + 1/2 O2(g) --> H2O(l) Ho/kJ = -285.85
C(s) + 2 H2(g) --> CH4(g) Ho/kJ = -74.85
a. +1189.76
b. +181.7
c. -181.7
d. -331.6
e. -1189.76
9. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction: 4 H2O(g) + 3 Fe(s) --> Fe3O4(s) + 4 H2(g)
H2(g) + 1/2 O2(g) --> H2O(g) Ho/kJ = -285.83
FeO(s) + 1/2 O2(g) --> Fe3O4(s) Ho/kJ = -302.4
FeO(s) + H2(g) --> Fe(s) + H2O(g) Ho/kJ = -13.8
a. -602.0
b. -391.7
c. +391.7
d. -24.8
e. +24.8
10. Which of the following equations represents a reaction that provides the heat of formation of hydroxylamine (NH2OH)?
a. NH3(g) + O(g) --> NH2OH(l)
b. ½ N2(g) + 1½ H2(g) + ½ O2(g) --> NH2OH(l)
c. N(g) + 3 H(g) + O(g) --> NH2OH(l)
d. N2(g) + 3 H2O2(l) --> 2 NH2OH(l) + 2 O2(g)
e. NH3(g) + 1/2 O2(g) --> NH2OH(l)
11. Which of the following equations represents a reaction that provides the heat of formation of ethanol (CH3CH2OH)?
a. 2 C(s) + 6 H(g) + O(g) --> CH3CH2OH(l)
b. 2 C(s) + 3 H2(g) + 1/2 O2(g) --> CH3CH2OH(l)
c. CH2 = CH2(g) + H2O(l) --> CH3CH2OH(l)
d. 2 CO(g) + 3 H2(g) --> CH3CH2OH(l) + 1/2 O2(g)
e. 2 CO2(g) + 6 H2(g) --> CH3CH2OH(l) + 3 H2O(l)
12. Which of the following equations represents a reaction that provides the heat of formation of hydrogen peroxide (H2O2)?
a. 2 H2O(l) --> H2O2(l) + H2(g)
b. H2(g) + O2(g) --> H2O2(l)
c. 2 H(g) + 2 O(g) --> H2O2(l)
d. H2O(l) + 12 O2(g) --> H2O2(l)
e. 2 H(g) + O2(g) --> H2O2(l)
13. Which of the following equations represents a reaction that provides the heat of formation of carbon dioxide (CO2)?
a. 2 CO(g) --> CO2(g) + C(s)
b. CO(g) + 1/2 O2(g) --> CO2(g)
c. C(s) + O2(g) --> CO2(g)
d. CO(g) + O(g) --> CO2(g)
e. C(s) + 2 O(g) --> CO2(g)
14. Which of the following equations represents a reaction that provides the heat of formation of hydrogen peroxide (H2O2)?
a. 2 H2O(l) --> H2O2(l) + H2(g)
b. H2(g) + O2(g) --> H2O2(l)
c. 2 H(g) + 2 O(g) --> H2O2(l)
d. H2O(l) + 12 O2(g) --> H2O2(l)
e. 2 H(g) + O2(g) --> H2O2(l)
15. Which of the following equations represents a reaction that provides the heat of formation of ethane (CH3CH3)?
a. CH2=CH2(g) + 2 H2(g) --> CH3CH3(g)
b. 2 CH4(g) --> CH3CH3(g) + H2(g)
c. 2 C(s) + 3 H2(g) --> CH3CH3(g)
d. 2 C(s) + 6 H(g) --> CH3CH3(g)
e. CH-CH(g) + 2 H2O(g) --> CH3CH3(g) + O2(g)

THERMOCHEMISTRY QUIZ Part II

1. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction: N2(g) + O2(g) --> 2 NO(g)
4 NH3(g) + 5 O2(g) --> 6 H2O(l) + 4 NO(g) Ho/kJ = -6134
NH3(g) + 3O2(g) --> 2 N2(g) + 6 H2O(l) Ho/kJ = -790
a. +177
b. +89
c. -89
d. -177
e. -1403
2. Calculate the value of Ho/kJ for the following reaction using the listed thermochemical equations: CuCl2(s) + Cu(s) --> 2 CuCl(s)
Cu(s) + Cl2(g) --> CuCl2(s) Ho/kJ = -206 kJ
2 Cu(s) + Cl2(g) --> 2 CuCl(s) Ho/kJ = -36 kJ
a. -242
b. -170
c. +121
d. +170
e. +242
3. Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction: XeF2(s) + F2(g) --> XeF4(s)
Xe(g) + F2(g) --> XeF2(s) Ho/kJ = -164
Xe(g) + 2 F2(g) --> XeF4(s) Ho/kJ = -262
a. -426
b. -213
c. -98
d. +98
e. +426
4. Calculate the value of Ho/kJ for the following reaction using the listed thermochemical equations: N2(g) + ½ O2(g) --> N2O(g)
2 NH3(g) + 3 N2O(g) --> 4 N2(g) + 3 H2O(l) Ho/kJ = -1010 kJ
4 NH3(g) + 3 O2(g) --> 2 N2(g) + 6 H2O(l) Ho/kJ = -1531 kJ
a. -489
b. -163
c. -81.5
d. +81.5
e. +163
5. Calculate Ho/kJ for the following reaction using the listed standard enthapy of reaction data: (C2H5)2O(l) --> C4H9OH(l)
C4H9OH(l)+6O2(g) --> 4 CO2(g) + 5 H2O(g) Ho/kJ=-2456.1 kJ
(C2H5)2O(l) + 6 O2(g) --> 4 CO2(g) + 5 H2O(g) Ho/kJ = -2510.0 kJ
a. -4966.1
b. -2483.1
c. -53.9
d. +53.9
e. +4966.1
6. Given the following equations and Ho values, determine the heat of reaction at 298 K for the reaction: P4(s) + 10 Cl2(g) --> 4 PCl5(g)
P4(s) + 6 Cl2(g) --> 4 PCl3(l) Ho/kJ = -1150
PCl3(l) + Cl2(g) --> PCl5(g) Ho/kJ = -111
a. +1261
b. +399
c. -399
d. -1261
e. -1594
7. Given the following equations and Ho values, determine the heat of reaction at 298 K for the reaction which occurs in a welder's acetylene torch:
2 C2H2(g) + 5 O2(g) --> 4 CO2(g) + 2 H2O(l)
H2(g) + 1/2 O2(g) --> H2O(l) Ho/kJ = -285.8
2 C(s) + H2(g) --> C2H2(g) Ho/kJ = +226.7
C(s) + O2(g) --> CO2(g) Ho/kJ = -393.5
a. -285.8
b. -571.6
c. -1574.0
d. -2145.6
e. -2599.0
8.Given the following equations and Ho values, determine the heat of reaction at 298 K for the reaction: C(s) + 2 H2(g) --> CH4(g)
C(s) + O2(g) --> CO2(g) Ho/kJ = -393.5
H2(g) + 1/2 O2(g) --> H2O(l) Ho/kJ = -285.8
CO2(g) + 2 H2O(l) --> CH4(g) + 2 O2(g) Ho/kJ = +890.3
a. +211.0
b. +74.8
c. -74.8
d. -192.2
e. -211.0
9. Calculate Ho/kJ for the following reaction using the listed standard enthapy of reaction data: 2 N2(g) + 5 O2(g) --> 2 N2O5(s)
N2(g) + 3 O2(g) + H2(g) --> 2 HNO3(aq) Ho/kJ = -414.0
N2O5(s) + H2O(l) --> 2 HNO3(aq) Ho/kJ = -86.0
2 H2(g) + O2(g) --> 2 H2O(l) Ho/kJ = -571.6
a. -42.2
b. -71.2
c. -84.4
d. -121.8
e. -243.6

THERMOCHEMISTRY QUIZ Part I

1. The statement which best describes a chemical reaction in which energy released is ….
a. exothermic and has a negative ΔH.
b. exothermic and has a positive ΔH.
c. endothermic and has a negative ΔH.
d. endothermic and has a positive ΔH.
2. When a chemical reaction occurs in which the products are more stable than the reactants ....
a. the potential energy of the reactants is completely transferred to the products.
b. the potential energy of the products is greater than the potential energy of the eactants.
c. the total amount of kinetic and potential energy of the chemicals in the reaction increases.
d. some of the potential energy of the reactants is transformed into kinetic energy.
e. the total amount of kinetic and potential energy of the chemicals in the reaction decreases.
3. The statement which gives the correct relationship between the sign of the change in internal energy and the system is ….
a. the change in internal energy is negative if Efinal is greater than Einitial.
b. The change in internal energy is positive if energy flows out of the surroundings and into the system.
c. The change in internal energy is positive if Einitial is greater than Efinal.
d. The change in internal energy is negative if energy flows out of the surroundings and into the system.
e. The change in internal energy is positive if energy flows out of the system and into the surroundings.
4. Which phase change is exothermic?
a. H2O(s) --> H2O(l)
b. H2O(l) --> H2O(s)
c. H2O(s) --> H2O(g)
d. H2O(l) --> H2O(g)
5. Which phase change is endothermic?
a. gas --> solid
b. gas --> liquid
c. liquid --> solid
d. liquid --> gas
6. The heat required to change 1 gram of a liquid at its normal boiling point to a gas at the same temperature is called the heat of ....
a. vaporization
b. fusion
c. reaction
d. formation
7. Solid A at 80 C is immersed in liquid B at 60 C. Which statement correctly describes the energy changes between A and B?
a. A releases heat and B absorbs heat.
b. A absorbs heat and B releases heat.
c. Both A and B absorb heat.
d. Both A and B release heat.
8. When ammonium chloride crystals are dissolved in water, the temperature of the water decreases. What does this temperature change indicate about the dissolving of ammonium chloride in water?
a. It is an endothermic reaction because it absorbs heat.
b. It is an endothermic reaction because it releases heat.
c. It is an exothermic reaction because it absorbs heat.
d. It is an exothermic reaction because it releases heat.
9. For a chemical reaction carried out at … the change in internal energy can be attributed to ….
a. constant volume; heat transfer
b. constant pressure; work
c. constant volume; work
d. constant pressure; heat transfer
e. constant volume; work and heat transfer
10. In order to ensure that comparisons of changes in enthalpy for reactions can be made, measurements of changes in enthalpy must be made under the conditions of ….
a. 298 K, 1 atm pressure, 1 M concentration for ions, and specified physical states.
b. 273 K, 1 atm pressure, 1M concentration, and specified physical states.
c. 298 K, 1 atm pressure, and 1 M concentration.
d. 273 K, 1 atm pressure, and 1M concentration.
e. 0°C, 1 atm pressure, 1M concentration, and specified physical states.

BOND ENERGY

Bond energies (BE) are defined as the energies required to break the chemical bonds of substances. So this is an endotermic process, the value is positive. In calculating the enthalpy change of a reaction, you can use the following formula :
DHreaction = SUM (BEreactants) - SUM (BEproducts)
Now do the following exercise :
The bond energy (kJ/mol) for H2, F2, and HF are 436, 158 and 568 kJ/mol respectively. Calculate the enthalpy change of : H2(g) + F2(g) --> 2 HF
Since bond energies are given, use the monoatomic gases.
After calculating the enthalpy change, draw a diagram.

STANDARD ENTHALPIES FORMATION

Using Formulas to Calculate enthalpy change.
The enthalpy change of a reaction can be calculated through the use of formulas. This formula depends on whether enthalpies of formation or bond energies are available.
When standard enthalpies of formation, DHfo, for all products and reactants are available, you have to use the following formula :
DHreaction = SUM (DHproducts) - SUM (DHreactants)
For simplicity in formulation, use DH to represent DHfo in the above formulas. D is delta, DH is enthalpy change, f is formation, and o is standard.
Calculate the enthalpy change of the following reactions by using a table of DHfo.
1. Calculate the enthalpy change of burning methane gas.
2. Calculate the combustion enthalpy of propane gas and butane gas.

HESS' LAW TASK

Hallo students, now you have to develop your understanding about Hess' law. Hess' law states about the summation of reaction, to sum the enthalpy change of step reactions in finding the enthalpy change of target reaction.

This diagram is an energy level diagram or named as an enthalpy diagram.

Look at the diagram, then write the step reactions and the target reaction. Okay, please do right now.

HESS' LAW

This is Germain Henry Hess. In the study of thermochemistry, there is an important law from him named 'HESS' LAW'. This is a principle of conservation of energy.

Hess' Law states that the heat evolved or absorbed in a chemical reaction is the same whether the reaction takes place in one or in several steps. This is also known as the law of constant heat summation.

Hess's law is important because it provides a practical way to combine thermochemical equations for known 'step' reactions to get a thermochemical equation for some 'target' reaction. The basic procedure is :
1. Write all the thermochemical equations for the step reactions.
2. Write the balanced chemical equation for the target reaction.
3. Reverse step reactions so products/reactants match the target reaction.
4. Scale step reactions so products/reactants that don't appear in the target reaction will cancel out.
5. Add the step reactions.
6. Scale the resulting reaction so it matches the target reaction

Okay students, you have to apply this law. Please find an exercise from your textbook and try to do summation of step reactions to find the enthalpy change of the target reaction. Firstly, do the simple equation, focus on 2 step reactions.

ENTHALPY DIAGRAMS

Write the thermochemistry equation for the forward and reverse reactions. What does the difference between these equations?


The following is another enthalpy diagram as another example to make you understand.

Write thermochemistry equation of the reaction as shown in the second diagram and describe the equation.

Make a conclusion for your explanation above.

ENTHALPY CHANGE

This diagram shows enthalpy changes.

Why the first arrow tell us that the enthalpy change of reaction is A --> B; and why the second arrow, the enthalpy change is proposed for the reverse reaction, B --> A.

Make a description to explain this evidence by using examples.

DETERMINING ENTHALPY CHANGE

Explain this picture clearly. Look at the calorimeter, there is a metal in the water.
Suggest the metal used in this reaction, find an experimental data and then determine the enthalpy change in kJ/mol.

CALORIMETRY TASK

This is a simple picture of calorimeter. This equipment used in the chemistry laboratory for estimating an enthalpy change in a reaction.
Your task is explaining the use of this equipment, plan an experiment by using this equipment. Choose a certain reaction, for example neutralisation reaction between strong acid, HCl(aq) and strong base, NaOH(aq).
Your explanation including how to use termometer; why there is a difference between the experimental data from scientist and your result.