Exam Style Answers 20 Asal Physics CB

 

 

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded may be different.

 Coursebook answers Chapter 20 7

Exam-style questions 1

B 

[1]

2

C 

[1]

3

a

i

6.02 × 1023 

 ii ii

Chlorine is diatomic, so 12.0 × 1023  [1] 1000 × N A = 6.02 × 1026  [1]

 iii iii

b

23

i  ii ii

4 × N A = 24.1 × 10   One C atom per molecule, so 24.1  10   Two O atoms per molecule, so 48.2 × 1023 

[1]

197 × 1.66 × 10−27 = 3.3 × 10−25 kg 

[1]

 iii iii

a

−25

5

1/(3.3 × 10

c

3.06 × 10 /6.02 × 10   = 5.08 mol ≈ 5.1 mol   p  pV  V  pressure p pressure  p2 =  1 1   V 2 105 ×140 =   = 3.4 × 105 Pa, or 42 3.3 atmospheres 

a

b

than in part a.   p1V 1   V  =  pV  2

 

8

9

Using pV  Using  pV  = nRT , we have

 

n = 

=

4.8 × 105 × 0.040

 

8.3 31 1× 293 RT  = 7.89 mol ≈ 7.9 mol 

b

Using pV  Using  pV  = nRT , we have

 

mass = 7.89 × 44 

 

= 347

 

[1] [1]

[1]

g ≈ 350 g 

[1]

Using pV  = nRT , we have  Using pV  nRT  1× 8.31 31× 273 −2 3 =    V =  V  = 2.25 × 10  m    p 1.01 0 1×105 Using pV  Using  pV  = NkT , we have [1]  p  p     = 

3.0 ×1026 × 1.38 ×10 0.200

23

−

×

400

 

[1] [1]

[1]

6

= 8.31 × 10

 Pa 

[1]

[1]

23

[1]

10 a

Using p  =  13  ρ , we have =  3 RT  

[1]

i 

b

[1]

Using pV  = nRT  Using pV  224 × 8.31 3 1× 315    p  =   p 1.50 = 3.91 × 105 Pa 

[1]

Any three from:

N the number of molecules 

−1

ms  

[1]

ratio of r.m.s. speeds hydrogen : oxygen = (mass of oxygen molecule / mass of hydrogen molecule)½  [1] = 3.99 ≈ 4.0 

[1]

An ideal gas is a gas that obeys the ideal gas law at all temperatures  [1]

 

and pressur pressures. es. 

b

i

125 (mol) 

[1]

 ii ii

125 × 6.02 × 1023 = 7.53 × 1025  (molecules) 

[1]

 pV  = nRT  

[1]

 iii iii

   

2

3. 42 42 ×10

No kinetic energy is lost in the collision. 

i

 ii ii

[1] 5

 

b

15 a

Molecules are in random motion / many impacts smear force over whole wall.  [1]

8.3 31 1× 276 = 224 mol 

13 a

[1]

31 × 300 V = 125 × 8.31   5 5 × 10

=

[1]

[1]

3

 0.62 m  

[1]

Cambridge International AS & A Level Physics – Sang, Jones, Chadha & Woodside © Cambridge University Press 2020