Page 43 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM

5 (a) 60 (b) (i) Volume of one argon atom
(b) 119.9 4 3
(c) 88.3% = 3 πr
4
STPM Practice 4 = π (0.192  10 ) m 3
–9 3
Objective Questions 3 –29 3
1 B 2 C 3 C 4 D 5 B = 2.96  10 m
6 D 7 D 8 B 9 D 10 B Volume of one mole of argon atom
23
–29
11 B 12 D 13 D 14 C 15 C = (2.96  10 )(6.02  10 )
–5
16 C 17 B 18 D 19 C 20 A = 1.78  10 m 3
21 A 22 A 23 B 24 D 25 B (ii) PV = nRT
26 B 27 B (101  10 )V = 1  8.31  273
3
–2
Structured and Essay Questions V = 2.25  10 m 3
1 (a) A gas that obeys the gas law: PV = nRT under all (iii) % = 1.78 × 10 –5
–2  100% = 0.079%
2.25 × 10
conditions
(b) (i) When temperature increases, the kinetic energy (iv) The volume of the gas molecules is indeed
of the particles increases. This leads to an negligible when compared to the volume
increase in the rate of collision with the walls of occupied by the gas.
the container. At the same time, the collisions 5 (a) Increasing pressure pushes the gas particles closer
are more energetic. to one another. The attractive force is then strong
(ii) Increasing pressure pushes the molecules closer enough to hold the particles together causing it to
to one another. This reduces the amount of condense.
empty space between the particles causing the (b) Presence of intermolecular hydrogen bonding pulls
volume to decrease. the molecules closer.
(iii) When temperature increases, the pressure (c) There are no intermolecular forces between gas
exerted by the gas will increase. To maintain the particles. They are free to move around and thus will
original pressure, the volume occupied by the distribute themselves throughout the container.
gas must increase so as to reduce the rate of (d) Going down the group, the size of the molecules gets
collision. bigger and the strength of the intermolecular forces
2 (a) PV = nRT between the molecules gets stronger causing the
(b) Presence of intermolecular forces. deviation to be more profound.
The gas particles have finite volume. (e) At high pressures, intermolecular repulsion exists
(c) Helium between the molecules. This makes the gas more
(d) At low pressures, intermolecular attraction operates difficult to compress.
between the molecules (In this case, it is the hydrogen At moderate pressures, intermolecular attraction
bonding). Thus, the volume actually occupied by the exists between the molecules, thus making them
gas is less than expected. This makes PV  nRT. easier to compress.
6 (a) Refer to text
PV
nRT (b) P (× 10 )/Pa 4 8 15 20
5
(b)
2
PV (× 10 )/Pa m 3 23.2 22.9 22.4 22.0
2
PV (× 10 )/Pa m 3
1 (a)
23.5
P
(e) High temperature and low pressure
23
3 Miscible: There are no intermolecular forces between the
gas particles.
Pressure: Collision of the gas particles with the walls of
the containers.
Compressible: No intermolecular forces and presence of
a lot of empty space.
22
4 (a) No intermolecular forces between gas particles. 0 2 4 6 8 10 12 14 16 18 20
5
P(× 10 )/Pa
The volume of the gas particles is negligible when
compared to the volume of the container in which
the gas is placed.

366

12 Answers.indd 366 3/26/18 4:06 PM