Science question bank 2011/2012/ Term 3
Formative assessment questions
Grade
Chapter
12
Chapter17 – Chemical
Equilibrium
Subject
Sections
Chemistry
17.1, 17.2
objectives
17.1.1 Compare between a reversible and irreversible reaction
17.1.2 Explain the meaning of a single or double arrow in chemical equations
17.1.3 Describe the chemical equilibrium
17.1.4 Apply the law of chemical equilibrium to write the equilibrium constant
expression for a homogeneous/ heterogeneous equilibria when a
chemical equation is provided
17.1.5 Calculate the value of Keq when the concentration of reactants and
products are given at a constant temperature
17.1.6 Relate between the value of Keq and the equilibrium position; i.e. favore
for products (forward reaction) or favore for reactants(reverse reaction)
17.2.1 State Le Chatelier principle
17.2.2 Apply Le Chatelier principle to explain the effect of changes in
concentration, changes in volume and pressure, changes in temperature,
and catalyst on the reaction equilibrium
Page 1 of 12
Multiple Choices
1. A reaction is at equilibrium when the rate of the forward and reverse
reactions are__________. (Obj. 17.1.1)
A.
Unequal
B.
Equal
C.
Different
D.
mixed
2. A homogeneous equilibrium reaction has reactants and products that
are_________________. (Obj. 17.1.4)
A.
in the same direction
B.
in the same potential energy
C.
in the same physical state
D.
in the same ratio
3. A heterogeneous equilibrium reaction has reactants and products that
are_____________. (Obj. 17.1.4)
A.
in different direction
B.
in different potential energy
C.
in different physical state
D.
different ratio
4. At equilibrium, the concentrations of reactants and products
are___________. (Obj. 17.1.3)
A.
in the same direction
B.
In the same quantities
C.
Constant
D.
not constant
Page 2 of 12
5. _______________states that at a given temperature, a chemical system
may reach a state in which a particular ratio of reactant and product
concentrations have a constant value. (Obj. 17.1.4)
A.
The law of chemical equilibrium
B.
The law of conservation of mass
C.
The law of chemical reaction
D.
The law of physical equilibrium
6. _____________is an expression that relates the concentrations of reactants
and products. (Obj. 17.1.5)
A.
Plus (+)
B.
equilibrium constant
C.
Change in time (Δt)
D.
Molar concentration
7. In an exothermic reaction, an increase in temperature favors
______________. (Obj. 17.2.2)
A.
The formation of both products and reactants
B.
The formation of reactants
C.
The formation of products
D.
The formation of the catalyst
8. In an endothermic reaction, an increase in temperature favors
______________. (Obj. 17.2.2)
A.
The formation of both products and reactants
B.
The formation of reactants
C.
The formation of products
D.
The formation of the catalyst
Page 3 of 12
9. A _____ reaction is a chemical reaction that can occur in both the forward
and reverse directions. (Obj. 17.1.1)
A.
Complete
B.
Forward
C.
Reversible
D.
Incomplete
10. A decrease in the concentration of reactants causes the rate of the _____
reaction to slow. (Obj. 17.2.2)
A.
Complete
B.
forward
C.
Reversible
D.
incomplete
11. The general equation for a reaction at equilibrium is as follows
(Obj. 17.1.4)
A.
aA + bB  cC + dD
B.
bA + aB  cC + dD
C.
aA + bB  dC + cD
D.
bA + aB  dC + cD
12. The equilibrium constant for this reaction at 700.0 K is 0.44.
H2O(g) + CO2(g)  H2(g) + CO2(g) What is the concentration of carbon
dioxide gas, if [H2O] = 0.16 mol/L, [CO2] = 0.15 mol/L and [H2] = 0.14
mol/L? (Obj. 17.1.5)
A.
0.00 14 mol/L
B.
0.075
C.
0. 16 mol/L
D.
0.75 mol/L
Page 4 of 12
13. Keq ___ 1: Products are favored at equilibrium. (Obj. 17.1.6)
A.
>
B.
<
C.
=
D.
+
14. Keq ___ 1: Reactants are favored at equilibrium. (Obj. 17.1.6)
A.
>
B.
<
C.
=
D.
+
15. What change can result in a shift in equilibrium during a reaction?
(Obj. 17.2.2)
A.
change in concentration
B.
change in temperature
C.
change in volume and pressure
D.
all of the above
16. In an endothermic reaction, lowering in temperature favors
______________. (Obj. 17.2.2)
A.
The formation of both products and reactants
B.
The formation of reactants
C.
The formation of products
D.
The formation of the catalyst
Page 5 of 12
17. In an exothermic reaction, lowering in temperature favors
______________. (Obj. 17.2.2)
A.
The formation of both products and reactants
B.
The formation of reactants
C.
The formation of products
D.
The formation of the catalyst
18. According to Le Chatelier’s principle, when the volume is increased, the
equilibrium shifts to the right. For which of the following reversible reactions is
this true? (Obj. 17.2.2)
A.
B.
C.
D.
19. According to Le Chatelier’s principle, when the volume is decreased, the
equilibrium shifts to the lift. For which of the following reversible reactions is
this true? (Obj. 17.2.2)
A.
B.
C.
D.
20. In the reaction
heat is evolved. What happens when
chlorine (Cl2) is added to the equilibrium mixture at constant volume ?
(Obj. 17.2.2)
A. equilibrium shifts to the left
B. equilibrium shifts to the right
C. equilibrium shifts to the enter
D. none
Page 6 of 12
21.
, When the temperature is increased the equilibrium
shifts in the ____________________ direction(s). (Obj. 17.2.2)
A. forward
B. reverse
C. forward and reverse
D. reactants
22. ____________________ is a state in which the forward and reverse
reactions __________each other because they take place at___________.
(Obj. 17.1.3)
A. Chemical equilibrium, cancel, equal rates
B. Chemical equilibrium, balance, equal rates
C. Chemical equilibrium, balance, different rates
D. Chemical equilibrium, oppose, equal rates
23. The equilibrium constant expression for the following reaction:
A (s) + 3B (g) + 5C (g) ↔ 2D (s) + 1E (l) (Obj. 17.1.4)
A. Keq = [E]1 [D]2/ [B]3
B. Keq = [D]2/ [B]3[C]5
C. Keq = [E]1 [D]2/ [B]3[C]5
D. Keq = [E]1 / [B]3[C]5
24. The reactants in the reverse reaction are on_________(Obj. 17.1.1)
A. above the arrows
B. under the arrows
C. the right of the arrows
D. the lift of the arrows
Page 7 of 12
25. The law of chemical equilibrium states that at a___________, a chemical
system might reach a state in which a particular _________of reactant and
product concentrations has a_________. (Obj. 17.1.3)
A. given pressure, masses, different value
B. given temperature, ratio, constant value
C. given volume, ratio, different value
D. given temperature, ratio, different value
26. The value of the equilibrium constant is constant for a given ____.
(Obj. 17.1.4)
A. temperature
B. pressure
C. volume
D. density
27. A change in ____ alters both the equilibrium position and the equilibrium
constant. (Obj. 17.1.4)
A. pressure
B. temperature
C. volume
D. density
28. The longer equilibrium arrow to the left or right mean? (Obj. 17.2.2)
A.
It means that, one reaction occurs faster than the other temporarily
B.
It means that, one reaction occurs faster than the other permanently
C.
It means that, both reaction occurs at the same time temporarily
D.
It means that, both reaction occurs at the same time permanently
Page 8 of 12
29. Which does NOT result in a shift of the equilibrium to the right?
(Obj. 17.2.2)
A. removing products
B. adding reactants
C. increasing concentration of reactants
D. adding products
30. Ethylene (C2H4) reacts with hydrogen to form ethane (C2H6). C2H4(g) +
H2(g) ↔ C2H6(g) + heat. How could you increase the amount of hydrogen in
the system? (Obj. 17.2.2)
A.
Increase the heat.
B.
Decrease the heat.
C.
Increase the C2H4.
D.
Decrease the C2H6
II Answer the following questions:
1. Given the reaction, at equilibrium, it was found that [C] = 0.20 mol/L, [D] =
0.55 mol/L, [A] = 0.30 mol/L and [B] = 0.48 mol/L. Calculate the value of Keq.
(Obj. 17.1.5)
Keq = 7.6 X 10-1
2. The reaction between nitrogen and oxygen produces nitrogen dioxide as
follows:
The value of the equilibrium constant for this reaction is
2.68. Calculate
A. [N2] in an equilibrium mixture containing 0.49 mol/L O2 and 0.64 mol/L N2O.
(Obj. 17.1.5)
Answer:
Page 9 of 12
B.[O2] in an equilibrium mixture containing 0.58 mol/L N2 and 0.86 mol/L N2O.
(Obj. 17.1.5)
Answer:
3. Write the equilibrium constant expression for the decomposition of baking
soda (sodium hydrogen carbonate). (Obj. 17.1.4)
↔
Keq = [CO2][H2O]
4. Write the expression for Keq of the following reaction: (Obj. 17.1.4)
A(s) + 3B(g) + 5C(g) + 8X(g)
Keq =
2D(s)+E(l) + 8F(g)
[F]8[E]1 / [B]3[C]5[X]8
5. In an equilibrium system at 800 K, if F 0.09 mol/L, P 0.13 mol/L, and Z
3.7 mol/L, calculate the equilibrium constant for the following reaction:
(Obj. 17.1.5)
F(g) + P(g)
2Z(g)
Page 10 of 12
6. Write the expression for the equilibrium constant for the following equilibria:
a.
(Obj. 17.1.4)
Answer:
b.
Answer:
c.
Answer:
(Obj. 17.1.4)
(Obj. 17.1.5)
III Short Answers
1. What three characteristics are common to all reactions that have reached
equilibrium.
(Obj. 17.1.3)
1. The reaction must take place in a closed system.
2. The temperature must remain constant.
3. All reactants and products are present and are in constant dynamic motion.
2. Explain what is meant by a stress on a reaction at equilibrium.
(Obj. 17.2.2)
Change in concentration
Change in volume/pressure
Change in temperature
3. Explain the meaning of this symbol Keq? (Obj. 17.1.4)
Keq is the equilibrium constant.
Keq is the numerical value of the ratio of product concentrations to reactant
concentrations (with each concentration raised to the power equal to its
coefficient in the balanced equation).
4. Explain the meaning of a double arrow in chemical equations. (Obj. 17.1.2)
The double arrow means that a reaction is at equilibrium and that the forward
reaction and the reverse reaction are occurring at the same rate.
Page 11 of 12
5.Compare homogeneous and heterogeneous equilibria. (Obj. 17.1.4)
In a homogenous equilibrium, all the reactants and products are in the same
physical state. In a het- erogeneous equilibrium, reactants and products are in
different physical states.
6. List three characteristics a reaction mixture must have if it is to attain a
state of chemical equilibrium. (Obj. 17.1.3)
To attain equilibrium, a reaction mixture must be in a closed container, it must
be at constant temperature, and all reactants and products must be present
Page 12 of 12