Homework 1- A
Question One: Draw a circle around the best answer
1. An exothermic reaction causes the surroundings to:
a) Become basic
b) Decrease in temperature
c) Condense
d) Increase in temperature
e) Decrease in pressure
2. In an endothermic process the heat (q) of the system has ......... sign
a. ±
b. negative (-)
c. positive (+)
3. If the enthalpy change for the reaction (ΔHrxn) 2 SO2(g) + O2(g) → 2 SO3(g) is -198 kJ, then the
ΔHrxn for the reaction SO2(g) + 1/2 O2(g) → SO3(g) will be
a. +198 kJ
b. - 99 kJ
c. + 99 kJ
d. - 198 kJ
4. The specific heat of aluminum is 0.90 J/g·oC. The energy, in joules, necessary to raise the
temperature of a 10.0 g piece of aluminum from 23.0 to 53oC is
a. 20.9 J
b. 9.0 J
c. 10.0 J
d. 90.0 J
5. When a work is done on a system it will be given a ......... sign
a. ±
b. negative (-)
c. positive (+)
6. An isolated system allows the transfer of ........... with its surrounding
a. mass.
b. energy
c. mass and energy
d. neither mass nor energy
7. The work done when a gas expands from 10 L to 20 L volume in vacuum will be:
a. 10 J
b. 0 J
c. 30 J
d. 200 J
8. An inert gas contract from 50 L to 20 L at a constant pressure of 1.0 atmosphere if a work of ..........
is done on it [1atm.L = 101.3 J]
a. + 3039 J
b. - 3039 J
c. + 5065 J
d. - 2026 J
9. When a gas under very high pressure expand adiabatically (no heat gain or loss q = 0), the
temperature of the surrounding will
a. increase
b. decrease
c. not change
d. double
10. The change in internal energy (∆E) is equal to the change in enthalpy (∆H) at constant
a. temperature
b. pressure
c. volume
d. none of the above
Question Two:
2.1 A 60.0 g sample of a metal was heated to 95.0 oC and then dropped into a beaker containing 50.0 g
of water at a temperature of 24.00oC. The temperature of the water rose to a final temperature of 27.00
oC. The specific heat of water is 4.184 J/g·oC. What is the specific heat of the alloy?
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2.2 Find the standard enthalpy of formation of ethylene, C2H4(g), given the following data:
C2H4(g) + 3 O2(g) ----> 2 CO2(g) + 2 H2O(l)
ΔHof = -1411 kJ;
C(s) + O2(g) ----> CO2(g)
ΔHof = -393.5 kJ;
H2(g) + ½O2(g) ----> H2O(l)
ΔHof = -285.8 kJ
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2.3 Calculate ΔHorxn for the combustion reaction of CH4 shown below
CH4(g) + 2 O2(g) ----> CO2(g) + 2 H2O(l)
given the following:
ΔHof CH4(g) = -74.8 kJ/mol;
ΔHof CO2(g) = -393.5 kJ/mol;
ΔHof H2O(l) = -285.5 kJ/mol.
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2.4 Complete
A state function is a mathematical function whose result depends only on the __________ and
__________ conditions, not on the process used. e.g.___________, _________ and _______________
2.5 How many grams of natural gas (CH4) must you burn to emit 267 kJ of heat?
CH4(g)+ 2O2(g) → CO2(g) + 2H2O(g)
ΔHrxn = -802.3 kJ/mol
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2.6 Calculate ΔH for the following reaction: CaO(s) + CO2(g) → CaCO3(s)
Use the following reactions and given ΔH’s.
Ca(s) + CO2(g) +1/2O2(g) → CaCO3(s)
ΔHrxn = -812.8 kJ
2Ca(s) + O2(g) → 2CaO(s)
ΔHrxn = -1268.8 kJ
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2.7
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Homework 1- B
Question One: Circle the best answer
1. The valence electrons for Cl atom are
a. 1
b. 3
c. 5
d. 7
2. Which of the following solids would have the lowest melting point?
a. KI
b. KBr
c. KCl
d. KF
3. The number of lone electron pairs in the N2 molecule is ___.
a. 1
b. 2
c. 4
d. 3
4. The C─ Cl bond in CCl4 is as ionic, polar covalent, or nonpolar covalent.
a. ionic
b.polar covalent
c. covalent
5. The bond Ca ─ Cl in CaCl2 can be classified as
a. ionic
b. polar covalent
c. covalent.
6.Which of the elements listed below has the greatest electronegativity?
a. Se
b. Sb
c. K
d. Ga
e. Fe
7. Which of the elements listed below is the least electronegative?
a. Sr
b. V
c. Ni
d. P
e. I
8. Which one of the following is most likely to be a covalent compound?
a. CsOH
b. NF3
c. Sr(NO3)2
d. CaO
e. LiF
9. Which one of the following is most likely to be an ionic compound?
a.NCl3
b.BaCl2
c. CO
d. SO2
e. SF4
10. Which of the following bonds is the shortest
a. N ─ H
b. N ─ C
c. N ══ C
d. N ≡ C
Question Two:
2.1 Write the Lewis dot symbol for the chloride ion, nitric acid (the three O's are bonded to the central
N)
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2.2 The Lewis structure for ozone is
. What is the formal charge for each atom?
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2.3 Draw the resonance structure for the molecule N2O3 (the atoms are arrangement is ONNOO
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2.4 Name five metals and five nonmetals that are very likely to form ionic compounds. Write formulas
for compounds that might result from the combination of these metals and nonmetals. Name these
compounds.
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2.5 Four atoms are arbitrarily labeled D, E, F, and G. Their electronegativities are as follows: D = 3.8,
E = 3.3, F = 2.8, and G = 1.3. If the atoms of these elements form the molecules DE, DG, EG, and DF,
how would you arrange these molecules in order of in- creasing covalent bond character?
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2.6 Classify the following bonds as ionic, polar covalent, or covalent, and give your reasons: (a) the
CC bond in H3CCH3, (b) the KI bond in KI, (c) the NB bond in H3NBC13, (d) the CF bond in CF4.
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2.7- Write Lewis structures for the following molecules and ions:
(a) OCS (b) CH3COO - (c) CN(d)CH3CH2NH3 + (e) OF2 (f) OH......................................................................................................................................................................
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2.8 The following Lewis structures are incorrect. Explain What is wrong with each one and give a
correct Lewis structure for the molecule. (Relative positions atoms are shown correctly.)
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Electronegativity values