GENERAL CHEMISTRY I
CHEM 1311.001
EXAM 4
Friday December 5, 1997

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1. Reactions with positive values of q (that is, q > 0)
a) absorb heatb) are exothermicc) release heat
d) both a and be) both b and c
2. Reactions with negative values of q (that is, q < 0)
a) absorb heatb) are exothermicc) release heat
d) both a and be) both b and c
3. True or False: It is sometimes possible to calculate the DH of a chemical reaction for which the DH can not be directly measured.
a) Trueb) False
4. A 346.85 g block of copper metal at 11.2 oC was heated to a temperature of 109.3 oC. How much heat was absorbed by the copper in order to achieve this result? Note that the specific heat of copper is 0.387 J / (g oC).
a) 4.13 kJb) 6.91 kJc) 8.64 kJ
d) 10.02 kJe) 13.17 kJ
5. A 516.63 g sample of water at 89.4 oC lost 36.8 kJ of heat. What was the temparature of the water after losing this amount of heat? Note that the specific heat of water is 4.18 J / (g oC).
a) 17.0 oCb) 25.4 oCc) 44.7 oC
d) 62.3 oCe) 72.4 oC
6. A 641.20 g sample of iron metal at 21.4 oC absorbed 3.18 kJ of heat. What was the temparature of the iron after absorbing this heat? Note that the specific heat of iron is 0.500 J / (g oC).
a) 9.9 oCb) 15.1 oCc) 31.3 oC
d) 54.8 oCe) 62.7 oC
7. Germanium forms two oxides: GeO and GeO2. Given below are thermochemical equations pertaining to these oxides:

2Ge(s)   +   O2(g)   ----->   2GeO(s)      DH = -510.0 kJ

Ge(s)   +   O2(g)   ----->   GeO2(s)      DH = -534.7 kJ

Use this information to find DH for the following reaction:

2GeO(s)   +   O2(g)   ----->   2GeO2(s)      DH = ?
a) -1579.4 kJb) -1044.7 kJc) -559.4 kJ
d) 559.4 kJe) 1579.4 kJ
8. Determine DH for the reaction of methane (CH4) with ammonia (NH3) as described by the following equation:

CH4(g)   +   NH3(g)   ----->   HCN(g)   +   3H2(g)      DH = ?

Make use of the following information:

N2(g)   +   3H2(g)   ----->   2NH3(g)    DH = -92.4 kJ

C(gr)   +   2H2(g)   ----->   CH4(g)      DH = -74.8 kJ

H2(g)   +   2C(gr)   +   N2(g)   ----->   2HCN(g)      DH = 270.3 kJ
a) 14.2 kJb) 256.2 kJc) 419.6 kJ
d) 437.5 kJe) 529.5 kJ
9. Make use of the data given in Table 5.2 to determine DH for the following reaction:

2CH3OH(l)   +   3O2(g)   ----->   2CO2(g)   +   4H2O(g)      DH = ?
a) -2231.4 kJb) -1277.0 kJc) -873.9 kJ
d) -396.7 kJe) 873.9 kJ
10. True or False: It is possible to experimentally determine the total amount of chemical potential energy (enthalpy) stored in a single chemical substance.
a) Trueb) False
ANSWERS:

1 a      2 e      3 a      4 e      5 e     

6 c      7 c      8 b      9 b      10 b

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