Physical Chemistry Answers

Question 15 : In a reaction:
2
A
→
B
+
2
C
2A→B+2C
, which of the statement is true?
Rate of formation of B = Rate of disappearance of A
Rate of disappearance of A = Rate of formation of C
Rate of disappearance of A = Rate of formation of B
Rate of formation of C= Rate of formation of B

Question 16 : A beaker with a mixture of ice and water is maintained at equilibrium:
H
2
O
(
s
)
+
h
e
a
t
→
H
2
O
(
l
)
H2O(s)+heat→H2O(l)
; If the temperature of the system is decreased:
No change occurs
The container cacks
Ice melts to form liquid water (shift to the right)
Water freezes to form ice (shifts to the left)

Question 17 : The term — dx/dt in the rate expression refers to the
Average rate of the reaction
increase in concentration of the reactants
instantaneous rate of the reaction
Change in concentration of the reactants with time

Question 12 : When extra
N
H
3
NH3
is added to the following system at equilibrium:
3
H
2
(
g
)
+
N
2
(
g
)
→
2
N
H
3
(
g
)
3H2(g)+N2(g)→2NH3(g)
, what happens?
Concentration of hydrogen decreases, but that of hydrogen increases
No change occurs
In order to restore equilibrium, the reaction shifts left, toward reactants
In order to restore equilibrium, the reaction shifts right, toward product

Question 13 : The minimum additional energy, above the average internal energy, which the reacting molecules must possess so that their collision result in a reaction is known as
Thermodynamic energy
Activation energy
Kinetic energy
Threshold energy

Question 14 : The factor that affects the rate of reaction is
Catalyst
All of these
Temperature of the reactants
Nature and concentration of the reactants

Question 9 : The rate of chemical reaction
Remains constant as reaction proceeds
Increases as the reaction proceeds
Decreases as the reaction proceeds
Both (a) and (b)

Question 10 : The reactions catalyzed by sunlight are called ____________ reactions
Exothermic
Sun-lighted
Endothermic
photochemical

Question 11 : The reaction below is exothermic:
2
S
O
2
(
g
)
+
O
2
(
g
)
→
2
S
O
3
(
g
)
2SO2(g)+O2(g)→2SO3(g)
. Le Chatelier's Principle predicts that __________ will result in an increase in the number of moles of
S
O
3
SO3
(g) in the reaction container.
decreasing the pressure
increasing the volume of the container
increasing the pressure
removing some oxygen

.Question 6 : Powdered marble reacts more rapidly with HCl than the chips of marble because:
Surface area of powdered marble is more that of chips of marble and hence there is more collisions between the molecules of reactants
Number of molecules increases.
Energy of activation decreases
Marble chips will not react with HCl

Question 7 : In the reaction:
2
B
→
P
r
o
d
u
c
t
2B→Product
; the rate equation is: Rate = k[B]. If the concentration of ‘B’ is doubled, the rate of reaction will increase by a multiple of
Four
Three
None of these
Two

Question 8 : For a reaction:
2
H
2
+
2
N
O
→
2
H
2
O
+
N
2
2H2+2NO→2H2O+N2
the rate law is
R
=
K
[
H
2
]
[
N
O
]
2
R=K[H2][NO]2
The Order of the reaction is?
2
3
0
1

.Question 4 : Equilibrium is a state of dynamic molecular behaviour, meaning that
reactants turn into products and products turn into reactants at different rates.
reactants turn into products and products turn into reactants at equal rates
products continually turn into reactants at a progressively faster rate.
the reaction eventually comes to a stop.

Question 5 : Milk sours more rapidly in summer than in winter because
in summer, the temperature Is high due to which effective collisions increase and hence the rate of reaction becomes fast
none of the above
in summer, the energy of activation decreases and hence the of reaction becomes fast
in winter, number of molecules per unit volume increases and hence the rate of reaction becomes fast

Question 1 : The reactions with the high value of energy of activation are
Slow
Fast
Not feasible
Moderate

Question 2 : In general, the rate of a reaction can be increased by all the factors except
Using a catalyst
Increasing the activation energy
Increasing the concentration of reactants
Increasing the temperature

Question 3 : For the following system at equilibrium, what will cause the partial pressure of HF to increase?
U
O
2
(
s
)
+
4
H
F
(
g
)
→
U
F
4
(
g
)
+
2
H
2
O
(
g
)
UO2(s)+4HF(g)→UF4(g)+2H2O(g)

decreasing the pressure
adding
U
F
4
(
g
)
UF4(g)

adding
U
O
2
UO2
(s)
removing
H
2
O
(
g
)
H2O(g)

Question 19 : Which of the following mixtures produces a buffer solution?
0.300 M
K
N
O
3
KNO3
+ 0.100 M NaCl (50 mL each)
0.400 M
C
H
3
C
O
O
H
CH3COOH
+ 0.100 M
C
H
3
C
O
O
N
a
CH3COONa
(50 mL each)
0.300 M
N
H
4
C
l
NH4Cl
+ 0.100 M HCl (50 mL each)
0.300 M NaOH + 0.100 M HCl (50 mL each)

Question 20 : The common-ion effect
promotes evaporation.
promotes condensation
reduces ionization.
increases solubility

Question 16 : Which of these is incorrect about the pH of a solution?
pH = -log
[
H
+
]
[H+]

an alkali has a higher pH value than an acid
The higher the pH, the more acidic the solution is
It is a measure of the acidity of the solution

Question 17 : How many coulombs of charge pass through a cell if 2.40 amperes of current are passed through the cell for 85.0 minutes?
204 C
2120 C
12200 C
0.133 C

Question 18 : Which of the followings is not a Bronsted acid?
HCl

H
2
S
O
4
H2SO4


A
l
C
l
3
AlCl3


H
N
O
3
HNO3

Question 12 : The pH of a neutral solution is
6
8
5
7

Question 13 : How long would a constant current of 18.0 amperes be required to flow in order for 9000. coulombs of charge to pass through a cell
50 s
0.002 s
200 s
500 s

Question 14 : The conjugate base of HCl is
HOCl

H
+
H+


O
H
−
OH−


C
l
−
Cl−


Question 15 : Buffering is:
all of these
due to LeChatelier's Principle
influenced by the common ion effect
is a process that is done by a solution made up of a weak acid and its salt

Question 8 : The magnitude of
K
w
Kw
indicates that __________.
water autoionizes very quickly
the autoionization of water is exothermic
water autoionizes very slowly
water autoionizes only to a very small extent

Question 9 : For the following reaction, which of the following is a conjugate acid-base pair?
H
C
2
O
−
4
(
a
q
)
HC2O4−(aq)
+
H
2
O
(
l
)
H2O(l)
→
→
H
3
O
+
H3O+
(aq) +
C
2
O
2
−
4
C2O42−
(aq)

H
2
O
H2O
and
C
2
O
4
2
−
C2O42−


H
C
2
O
−
4
HC2O4−
and
H
3
O
+
H3O+


H
C
2
O
−
4
HC2O4−
and
C
2
O
2
−
4
C2O42−


H
C
2
O
−
4
HC2O4−
and
H
2
O
H2O


Question 10 : What’s the concentration of Ag+ ion in a saturated silver chloride solution?
K
s
p
Ksp
= 1.56 x
10
−
10
10−10
.
none of these
0.000339 M
0.0000125 M
4.90 M

Question 11 : A substance that is capable of acting as both an acid and as a base is _____.
conjugated
Amphoteric
Diprotic
Binary acid-base