Chemistry 1A Fall 2014 MWF 12:30
1.
Midterm 2
Test Form A
When the following reaction is balanced in acidic solution, using the smallest whole-number
+
coefficients, what is the coefficient of H ?
Zn(s) + NO3–(aq) → Zn2+(aq) + NH4+(aq)
A)
B)
C)
D)
E)
0
9
10
12
none of these
Ans: C
2.
When the reaction Cl2 → Cl– + ClO3– (basic solution) is balanced, using the smallest whole-number
–
coefficients, what is the coefficient of Cl ?
A) 2
B) 3
C) 4
D) 5
E)
6
Ans: D
3.
The volume of a balloon is 3.78 L at 22.8°C. The balloon is heated to 42.4°C. Calculate the new
volume of the balloon.
A) 7.03 L
B) 4.03 L
C) 2.03 L
D) 3.55 L
E)
3.78 L
Ans: B
4.
A balloon contains 5.0 g of argon gas. With the temperature kept constant, 5.0 g of neon gas is
added. What happens?
A) The balloon doubles in volume.
B) The volume of the balloon expands by more than 2 times.
C) The volume of the balloon expands by less than 2 times.
D) The balloon stays the same size, but the pressure increases.
E)
none of these
Ans: B
5.
The volume of a helium balloon is 1.85 L at 24.0°C and 1.00 atm at sea level. The balloon is
released and floats upward. At a certain altitude, the balloon has a volume of 2.14 L and the
temperature is 15.2°C. What is the atmospheric pressure at this altitude?
A) 0.538 atm
B) 0.839 atm
C) 0.891 atm
D) 1.36 atm
E)
none of these
Ans: B
6.
Which of the following relationships is not true?
A) PV = constant when temperature and moles of gas are held constant.
B) V/T = constant when pressure and moles of gas are held constant.
C) nT = constant when pressure and volume are held constant.
D) P/n = constant when volume and temperature are held constant.
E)
All of these are true.
Ans: E
7.
Three 1.00-L flasks at 25°C and 725 torr contain the gases CH4 (flask A), CO2 (flask B), and
C 2H 6 (flask C).
In which flask is there 0.039 mol of gas?
A) flask A
B) flask B
C) flask C
D) all
E)
none
Ans: D
8.
A gas mixture contains 30% Ar and 70% CO2 by volume. Calculate the mass of CO2 in a 4.0-L
bottle of this mixture at 1.0 atm, 25°C.
A) 60.0 g
B) 7.19 g
C) 2.16 g
D) 5.04 g
E)
none of these
Ans: D
9.
The density of a certain diatomic gas is 1.43 g/L at STP (1.00 atm and 273K). Identify the gas.
A) H2
B) N2
C) Cl2
D) F2
E)
O2
Ans: E
10.
Potassium chlorate decomposes upon heating as follows:
2KClO3(s) → 2KCl(s) + 3O2(g)
A 2.36-g sample of KClO3 (122.6 g/mol) decomposes, and the oxygen at 23.8°C and 0.930 atm is
collected. What volume of oxygen gas will be collected, assuming complete reaction?
A)
B)
C)
D)
E)
0.504 L
1.93 L
0.756 L
0.0607 L
0.0404 L
Ans: C
11. Consider three 1.0-L flasks at STP. Flask A contains N 2 gas, flask B contains Kr gas, and flask C
contains He gas.
In which flask do the gas particles have the lowest average kinetic energy?
A) flask A
B) flask B
C) flask C
D) The pas particles in all of the flasks have the same average kinetic energy.
E)
The gas particles in two of the flasks have approximately the same average kinetic energy.
Ans: D
12.
At equivalent temperature, which gas molecules have the highest average velocity?
A) He
B) Cl2
C) CH4
D) NH3
E)
The molecules of all the gases have the same average velocity.
Ans: A
13.
The root-mean-square velocity of Cl2 gas at 30°C is
A) 326 m/s.
B) 102 m/s.
C) 32.4 m/s.
D) 10.3 m/s
E)
3.25 m/s
Ans: A
14.
Indicate the equilibrium expression for the following reaction:
2X(g) + Y(g)
3W(g) + 2V(g)
A)
B)
[X]2[Y][W]3[V]
3
2
!W # ! V #
" $" $
2
!X# !Y#
" $" $
C)
!3W #!2V#
" $" $
!2X#!Y#
" $" $
D)
[X] [Y]
3
[ W ] [V ]
2
Ans: B
15.
Equimolar amounts of the gases N2 and H2 are mixed in a closed container fitted with a piston
(allowing the volume of the container to change, thus keeping the pressure constant). Calculate the
ratio of the final volume of the container to the initial volume of the container when the following
reaction goes to completion.
N2 + 3H2 → 2NH3
A) 2/3
B) 3/2
C) 4/3
D) 1/3
E)
none of these
Ans: A
16.
The equilibrium constant for A + 2B
3C is 1.0 × 10-6.
Determine the equilibrium constant for 2A + 4B
6C.
A)
B)
C)
D)
E)
Ans: D
4.0 × 10-6
4.0 × 10-12
1.0 × 10-6
1.0 × 10-12
1.0 × 1024
17.
Calculate the equilibrium H+ concentration of a 1.68 M solution of acetic acid (CH3CO2H, K = 1.8 ×
10–5 M) that dissociates according to the reaction:
CH3CO2H
A)
B)
C)
D)
E)
H+ +
CH3CO2
-
8.48 x 10-3 M
7.56 x 10-6 M
1.62 x 10-12 M
5.50 x 10-3 M
2.64 x 10-9 M
Ans: D
18.
Which of the following is an example of a homogeneous equilibrium?
A) NH4NO3(s)
N2O(g) + 2H2O(g)
B) H2(g) + I2(s)
2HI(g)
C) CaCl2(s) + 2H2O(g)
CaCl2•2H2O(s)
D) 2N2O(g) + N2H4(g)
3N2(g) + 2H2O(g)
E)
none of these
Ans: D
19.
Consider the following reaction:
2HF(g)
H2(g) + F2(g) (K = 1.00 × 10–2)
Given 1.06 mol of HF(g), 0.820 mol of H2(g), and 1.12 mol of F2(g) are mixed in a 5.00-L flask,
determine the reaction quotient, Q, and the net direction to achieve equilibrium.
A)
B)
C)
D)
E)
Q = 0.866; the equilibrium shifts to the right.
Q = 0.817; the equilibrium shifts to the left.
Q = 0.866; the equilibrium shifts to the left.
Q = 0.817; the equilibrium shifts to the right.
Q = 1.37; the system is at equilibrium.
Ans: B
20.
At a given temperature, the equilibrium constant K for the reaction
2SO2(g) + O2(g)
9
2SO3(g)
is 3.0 × 10 . If 2.80 mol of SO2 and 4.06 mol of O2 are placed in a 1.78-L container and allowed to
react to equilibrium at this temperature, what is the concentration of SO3 at equilibrium?
A)
B)
C)
D)
E)
Ans: B
2.28 M
1.57 M
3.85 M
0.708 M
3.15 M
21.
Consider the following reaction (assume an ideal gas mixture).
2NOBr(g)
2NO(g) + Br2(g)
A 3.0-L vessel was initially filled with pure NOBr, at a pressure of 3.6 atm, at 300 K.
After equilibrium was reached, the volume was increased to 5.0 L, while the temperature was kept at
300 K. This will result in:
A) an increase in Kp.
B) a decrease in Kp.
C) a shift in the equilibrium position to the right.
D) a shift in the equilibrium position to the left.
E)
none of these
Ans: C
22.
Carbon dioxide (CO 2) decomposes according to the following reaction:
2CO 2
2CO + O 2
CO 2 is placed in a container at an initial pressure of 2.00 atm. After equilibrium is
reached, the total pressure is found to be 2.75 atm. What is K p for this reaction?
A) 6.75
B) 1.12
C) 0.281
D) 1.69
E) 2.25
Ans: A
23.
Ans: D
For the reaction below, K = 4.00
SO 2 + NO 2
SO 3 + NO
If all four gases start at the same concentration of 2.0 M, what will be the
concentration of SO 2 when the system reaches equilibrium?
A) 1.00 M
B) 2.67 M
C) 2.00 M
D) 1.33 M
E) 4.00 M