# Chapter 1

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```					Practice questions

Chapter 7
Ordinary Matter

-27
1 unified atomic mass unit = 1.66 × 10                           kg
-23         -1
k = 1.38 × 10                JK
-1          -1
R = 8.31 JK mol
23
Avogadro's number = 6.02 × 10

1. Figure 7.a shows how the resultant force, F, between two neighbouring atoms in a pure
metal varies with separation, x.
a

[Fig 7.a]
With reference to Fig 7.a, state:

i      the range of values of x over which the resultant force is attractive.
............................................................................................................................... [1]

ii     the value of x for equilibrium separation.
............................................................................................................................... [1]

iii State the maximum attractive force Fmax between two neighbouring atoms.
............................................................................................................................... [1]

iv State the spacing xF between the atoms for this maximum force.
............................................................................................................................... [1]

1(5)
b A wire of diameter 2.00 mm is made from this metal. Using the spacing xF, and
assuming all atoms have this spacing, estimate

i    the number of atoms in a single cross-sectional layer of the wire
.....................................................................................................................................

............................................................................................................................... [2]

ii   the theoretical maximum breaking force of the wire.
.....................................................................................................................................

............................................................................................................................... [2]

iii Give two reasons why your answer in b.ii is much larger than can be achieved in
a real wire.
.....................................................................................................................................

............................................................................................................................... [2]

[Total: 10]

2. a Figure 7.a shows how the force between neighbouring atoms varies with separation.

i    Sketch a similar graph to show how potential energy varies with separation
between two atoms.

............................................................................................................................... [2]

ii   Explain the shape of the graph.
.....................................................................................................................................

............................................................................................................................... [2]

b The model is applicable to the case of a metal solid. State how the four quantities, molar
volume, molar latent heat of fusion, linear expansivity and compressibility, are related to
the shapes of the potential energy versus separation and force versus separation
graphs.
.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

............................................................................................................................... [4]

[Total: 8]

2(5)
3. a Estimate the diameter of an atom of gold given that the atomic mass of gold is 197 and
4    -3
its density is 1.93 x 10 kg m .
.....................................................................................................................................

............................................................................................................................... [2]

b Outline how observations made using X-ray diffraction can be used to determine a
value for the diameter of a gold atom.
.....................................................................................................................................

............................................................................................................................... [2]

[Total: 4]

4. a

i    One of the assumptions of the kinetic theory of gases is that molecules make
elastic collisions. State what is meant by an elastic collision.
.....................................................................................................................................

.....................................................................................................................................

............................................................................................................................... [1]

ii   State three more assumptions that are made in the kinetic theory of gases.
.....................................................................................................................................

.....................................................................................................................................

............................................................................................................................... [3]

b One mole of hydrogen at a temperature of 470 K is mixed with one mole of nitrogen at
350 K. such that after a short period of time the mixture is in thermal equilibrium.

i    Explain what happens as the two gases approach and then reach thermal
equilibrium.
.....................................................................................................................................

............................................................................................................................... [2]

ii   Calculate the average kinetic energy of the hydrogen molecules before they are
mixed with the nitrogen molecules.
.....................................................................................................................................

............................................................................................................................... [2]

[Total: 8]

3(5)
5. The tyres of a car are pumped up to a pressure of 0.179 MPa above atmospheric
pressure. The air in the tyres is at a temperature of 18°C. What is the pressure in the tyres
after a journey such that the air in the tyres has risen to a temperature of 25 °C? (Give
your answer to 3 s.f. and assume the volume within each tyre remains constant.)
................................................................................................................................

.....................................................................................................................................

............................................................................................................................... [3]

[Total: 3]

6. Eight students were asked to read the atmospheric pressure PA on the pressure gauge
which had calibrations every 2 kPa. The values they obtained in kPa were: 104, 105,
106,105, 104,106, 104, 104
a Estimate the uncertainty in measuring PA.
............................................................................................................................... [1]

b Calculate the percentage uncertainty in the average reading.
............................................................................................................................... [1]

c What would be the percentage uncertainty if the pressure being measured were 3PA?
.....................................................................................................................................

............................................................................................................................... [1]

[Total: 3]

7. A pressurized tank at 23.0 °C contains 3.00 mole of argon gas (relative atomic mass of
argon =40.0). Calculate
a the root-mean-square speed of the argon atoms
.....................................................................................................................................

............................................................................................................................... [3]

b the total kinetic energy of the gas.
.....................................................................................................................................

............................................................................................................................... [2]

[Total: 5]

8. A small pollen grain suspended in a gas is struck successively by six gas molecules
-1        -1          -1        -1         -1            -1
whose speeds are 400 m s , 500 m s , 400 m s , 200 m s , 600 m s and 200 m s .
Calculate the root mean square speed of the five molecules.
.....................................................................................................................................

.....................................................................................................................................

............................................................................................................................... [2]

[Total: 2]

4(5)
9. The number of molecules in one cubic metre of air decreases as altitude increases. The
table shows how the pressure and temperature of air compare at sea-level and at an
altitude of 12 km

Altitude/km                            Pressure/kPa                       Temperature / °C
0                                    100                                  17
12                                     14                                 -58

a Calculate the number of moles of air in a cubic metre of air at

i    sea-level
.....................................................................................................................................

............................................................................................................................... [2]

ii   12 km.
.....................................................................................................................................

............................................................................................................................... [2]

b Assume that in air at both heights the proportion of oxygen molecules is 23%. Calculate
the number of extra oxygen molecules there are per cubic metre at sea-level compared
with per cubic metre at an altitude of 10 000 m.
.....................................................................................................................................

............................................................................................................................... [2]

[Total: 6]

[Overall Total: 59]

5(5)

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