(a) List two differences between solids and liquids. (b) The graph below is the heating curve for a solid X. Use the graph to answer Questions (i) — (iii) b...
Question 1 Report
(a) List two differences between solids and liquids.
(b) The graph below is the heating curve for a solid X. Use the graph to answer Questions (i) — (iii) below.
(i) What is the melting point of X?
(ii) If the vapour of X is cooled, at what temperature will it start to condense?
(iii) (I) As X is heated, state what happens to the: I. frequency of collision of molecules of X;
(II) value of the entropy of the system.
Answer Details
(a) Two differences between solids and liquids
| Solids | Liquids |
|---|---|
| Have a definite (fixed) shape of their own. | Have no definite shape; they take the shape of the container. |
| Particles are closely packed and held in fixed positions, so solids are almost incompressible and do not flow. | Particles are more loosely held and can slide over one another, so liquids flow. |
(b) The heating curve for solid X is shown below. Each horizontal (flat) portion is a change of state, where the added heat is used to break the forces between particles instead of raising the temperature.
(i) Melting point of X
The melting point is the temperature of the first flat portion of the curve, where the solid is turning into liquid at constant temperature.
\[ \text{Melting point of X} = 60\,^{\circ}\text{C} \](ii) Temperature at which the vapour of X starts to condense
Condensation is the reverse of boiling, so the vapour condenses at the boiling point of X. This is the temperature of the second flat portion of the curve.
\[ \text{Condensation temperature} = 210\,^{\circ}\text{C} \](iii) As X is heated:
(I) Frequency of collision of molecules of X: it increases. Heating gives the molecules more kinetic energy, so they move faster and collide with one another more often.
(II) Value of the entropy of the system: it increases. As X changes from solid to liquid to gas the particles become more disordered and more freely arranged, so the entropy of the system rises.
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