CHEM101 Fall12 Exam III (a)
On the answer sheet (scantron) write yourname, student ID number, and lab section number. Choose
the best (most correct) answer for each question and enter it on your answer sheet.
Potentially useful data:
Avogadro’s Constant:6.022 × 10 23 mol -1
specific heat ofwater = 4.18 J g -1 °C -1
specific heat ofsteam = 2.00 J g -1 °C -1
enthalpyof fusion of water = 333 J/g
enthalpyof vaporization of water = 2260 J/g
1. Please choose theletter “a” as youranswer for this question.
2. How much energyis required to convert 35.0 g of water at 27.5°C to steam at 155.0°C?
a. 1.87 x10 J4
b. 9.35 x10 J4
c. 9.78 x10 J
d. 2.89 x10 J5
e. 6.35 x10 J4
3. Based on the following physicochemical equation, which statement is false?
NH (3) → NH (g) 3 ∆H°=+23.4kJ
a. The physicochemicalequation represents a physical change.
b. The enthalpychange for the gas condensing into a liquid is known.
c. The internal energyof the surroundings increases.
d. The enthalpychange is determined at constant pressure.
e. The enthalpychange is endothermic.
4. A chemical reaction that absorbs heat from the surroundings is said to
be________ and has __________ ∆H at constant pressure.
a. endothermic; positive
b. endothermic, negative
c. exothermic, negative
d. exothermic, positive
e. exothermic, neutral
Page 1 of 6 5. The enthalpychangefor the following reactionis −483.6 kJ:
2 H2(g) + O 2g) → 2 H O(2)
Therefore, the enthalpychange for the following reaction is:
4 H2(g) + 2 O 2g) → 4 H O(2)
c. 2.34 × 10 kJ
d. 483.6 kJ
e. 967.2 kJ
6. What is the enthalpychange when 175 g of C H are burned in excess O ?
3 8 2
C H (g) + 5 O (g) → 3 CO (g) + 4 H O(l) ∆H°=−2220kJ
3 8 2 2 2
a. −1.71 x10 kJ
−3.47 x10 kJ
d. −3.89 x10 kJ
−8.82 x10 kJ
7. The value of ΔH° for the reaction below is +128.1 kJ:
CH O3(l) → CO(g)+ 2 H (g) 2
How manykJ of heat are consumed when 5.10 g of H (g)2is formedas shown in the equation?
a. 162 kJ
b. 62.0 kJ
c. 128 kJ
e. 326 kJ
8. Which of the following statementsis false?
a. Breaking bonds is exothermic.
b. Bond enthalpiesquantify the energy change for the complete separationof two
bonded atoms in a molecule at constantpressure.
c. Bond enthalpyvalues are based on molecules in the gas phase.
d. Breaking weak bonds and making an equal number of strong bonds is exothermic.
e. Breaking strong bonds and making a lesser number of equallystrong bonds is
Page 2 of 6 9. The temperature of 3.50 kg of water is raised by 1.17 °C when 1.00 g of hydrazine, N2 4, is
burned in a bomb calorimeter. The bomb has a heat capacityof 883 J/°C. How much heat is
given off by the sample?
a. 0.944 kJ
b. 16.3 kJ
c. 17.1 kJ
d. 18.2 kJ
e. 21.5 kJ
10.A 0.100 mole sample of CH re4cts completelyin a bomb calorimeter witha heat capacityof
the bomb equal to 783 J/°C. The calorimeter contains254 g of water. Determine the
temperature increase of the calorimeter.
CH 4g) + 2 O 2g) → 2 H O(g2 + CO (g) 2 ∆H°=−802.3kJ
4.35 x 10 °C
b. 7.56 °C
c. 10.2 °C
e. 43.5 °C
11. Determine the heat of reaction for the process
C2 4(g) + 6 HCl(g) → 2 CHCl (g) 3 4H (g) 2
using the information given below:
2 C(s) + 2 H2(g) → C H2 4) ∆H°=52.3kJ
H (g) + Cl (g) → 2 HCl(g) ∆H°=−184.6kJ
C(s) + ½ H 2g) + 3/2 Cl2(g) → CHCl (g)3 ∆H° = −103.1kJ
d. +295.3 kJ
e. +398.4 kJ
12. In the reaction below, ∆Hf° is zero for .
Ni(s) + 2 CO(g) + 2 PF3(g) → Ni(CO) (PF2) (l3 2
c. PF 3g)
d. Ni(CO) (2F )3 2)
e. none of the above
Page 3 of 6 13. The standard enthalpies of formation for several substancesare given below:
FeS 2s)=−178.2kJ/mol FeCl 2s)=−341.8kJ/mol
FeCl 3s)=−399.5kJ/mol HCl(g)=−92.3kJ/mol
HCl(aq)=−167.1kJ/mol H 2(g)=−20.6kJ/mol
Calculate the ∆H° forthe reactionbelow.