CHM141- Exam 3

Name: ________________________ Class: ___________________ Date: __________ ID: A


Midterm 3 sample

Equations and constants
Ideal gas law: pV = nRT [gas constant R = 0.08206 L·atm/(mol·K)]
p1/p2=T1/T2 p1V1=p2V2 V1/T1=V2/T2 V1/n1=V2/n2
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Temperature units: T(K) = T( C)+273.15
Pressure units: 760 mm Hg = 1 atm = 101.3 kPa
Density: d = m / V = p  MW / RT
KE = 1/2*m*v2 Gasses have the same KE at the same temperature
q = cmT (c: specific heat capacity, m: mass, T: temperature change) Cwater = 4.18 J/gK
Heat of physical state change: q = H  m or H  n
Hr   
n   f H (products)  n   f H (reactants)
Multiple Choice (5 pts each)
Identify the choice that best completes the statement or answers the question.

____ 1. Which one of the following statements is INCORRECT?
a. Energy is neither created nor destroyed in chemical reactions.
b. Kinetic energy is the energy that results from an object’s composition.
c. Endothermic processes transfer heat from the surroundings into the system.
d. Increasing the thermal energy of a gas increases the motion of its atoms.
e. Energy is the capacity to do work.

____ 2. The heat of vaporization of benzene, C 6H6, is 30.7 kJ/mol at its boiling point of 80.1 C. How much energy in
the form of heat is required to vaporize 3.00 mol benzene at its boiling point?
a. 0.302 kJ
b. 92.1 kJ
c. 61.4 kJ
d. 40.1 kJ
e. 3.14  103 kJ

____ 3. Calculate rH for the combustion of ammonia,
4 NH3(g) + 7 O2(g)  6 H2O(™ ) + 4 NO2(g)
using standard molar enthalpies of formation.

molecule fH (kJ/mol-rxn)
NH3(g) –45.9
NO2(g) +33.1
H2O(™) –285.8

a. +30.24 kJ/mol-rxn
b. –206.9 kJ/mol-rxn
c. –298.6 kJ/mol-rxn
d. –1399 kJ/mol-rxn
e. –1664 kJ/mol-rxn




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, Name: ________________________ ID: A


____ 4. The lid is tightly sealed on a rigid flask containing 2.25 L Ar at 22 C and 0.977 atm. If the flask is heated to
44 C, what is the pressure in the flask?
a. 2.86 atm
b. 1.47 atm
c. 1.05 atm
d. 0.769 atm
e. 1.73 atm

____ 5. Which of the following relationships is/are CORRECT for gases?
1. The amount of a gas (in moles) is directly proportional to its volume (at constant
temperature and pressure).
2. The pressure of a gas is directly proportional to its temperature in kelvin (at constant
volume and moles).
3. The volume of a gas is inversely proportional to its temperature in kelvin (at constant
pressure and moles).

a. 1 only
b. 2 only
c. 3 only
d. 1 and 2
e. 1 and 3

____ 6. Place the following gases in order of increasing average velocity at 300 K: Ar, CH 4, N2, and CO.
a. Ar = CH4 = N2 = CO
b. CO < Ar < N2 < CH4
c. CO = N2 < CH4 < Ar
d. Ar < CO = N2 < CH4
e. CH4 < N2 = CO < Ar

____ 7. A hot piece of iron is dropped into a beaker containing colder water. Which of the following statements is/are
CORRECT?
1. Energy is transferred as heat from the water to the iron.
2. Thermal equilibrium is attained when the iron and the water reach the same
temperature.
3. Thermal energy from the iron is converted to electrostatic energy in the water.

a. 1 only
b. 2 only
c. 3 only
d. 1 and 2
e. 1, 2, and 3

____ 8. Specific heat capacity is defined as
a. the amount of heat required to raise the temperature of 1 gram of substance by 1 degree.
b. the amount of heat required to raise the temperature of a substance by 1 K.
c. the amount of heat required to vaporize a solid or liquid.
d. the maximum amount of heat that a substance may absorb without decomposing.
e. 4.18 cal/gK.




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